CKA Flashcards
Pre setup steps?
in .bashrc
alias k=kubectl
export do=”–dry-run=client -o yaml”
export now=”–force –grace-period 0”
in .vimrc
set ts=2
set sts=2
set sw=2
set expandtab
set syntax on
You have access to multiple clusters from your main terminal through kubectl contexts. Write all those context names into /opt/course/1/contexts.
Next write a command to display the current context into /opt/course/1/context_default_kubectl.sh, the command should use kubectl.
Finally write a second command doing the same thing into /opt/course/1/context_default_no_kubectl.sh, but without the use of kubectl.
/opt/course/1/contexts
k config get-contexts -o name > /opt/course/1/contexts
/opt/course/1/context_default_no_kubectl.sh
cat ~/.kube/config | grep current
Use context: kubectl config use-context k8s-c1-H
Create a single Pod of image httpd:2.4.41-alpine in Namespace default. The Pod should be named pod1 and the container should be named pod1-container. This Pod should only be scheduled on controlplane nodes. Do not add new labels to any nodes.
find controlplane node
$ k get node
get controlplane node taints
k describe node cluster1-controlplane1 | grep Taint -A1
get controlplane node labels
$ k get node cluster1-controlplane1 –show-labels
check the export on the very top of this document so we can use $do
$ k run pod1 –image=httpd:2.4.41-alpine $do > 2.yaml
$ vim 2.yaml
2.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: pod1
name: pod1
spec:
containers:
- image: httpd:2.4.41-alpine
name: pod1-container # change
resources: {}
dnsPolicy: ClusterFirst
restartPolicy: Always
tolerations: # add
- effect: NoSchedule # add
key: node-role.kubernetes.io/control-plane # add
nodeSelector: # add
node-role.kubernetes.io/control-plane: “” # add
status: {}
create pod
$ k -f 2.yaml create
$ k get pod pod1 -o wide
NAME READY STATUS RESTARTS … NODE NOMINATED NODE
pod1 1/1 Running 0 … cluster1-controlplane1 <none></none>
Use context: kubectl config use-context k8s-c1-H
There are two Pods named o3db-* in Namespace project-c13. C13 management asked you to scale the Pods down to one replica to save resources.
If we check the Pods we see two replicas:
➜ k -n project-c13 get pod | grep o3db
o3db-0 1/1 Running 0 52s
o3db-1 1/1 Running 0 42s
From their name it looks like these are managed by a StatefulSet. But if we’re not sure we could also check for the most common resources which manage Pods:
➜ k -n project-c13 get deploy,ds,sts | grep o3db
statefulset.apps/o3db 2/2 2m56s
Confirmed, we have to work with a StatefulSet. To find this out we could also look at the Pod labels:
➜ k -n project-c13 get pod –show-labels | grep o3db
o3db-0 1/1 Running 0 3m29s app=nginx,controller-revision-hash=o3db-5fbd4bb9cc,statefulset.kubernetes.io/pod-name=o3db-0
o3db-1 1/1 Running 0 3m19s app=nginx,controller-revision-hash=o3db-5fbd4bb9cc,statefulset.kubernetes.io/pod-name=o3db-1
To fulfil the task we simply run:
➜ k -n project-c13 scale sts o3db –replicas 1
statefulset.apps/o3db scaled
➜ k -n project-c13 get sts o3db
NAME READY AGE
o3db 1/1 4m39s
Use context: kubectl config use-context k8s-c1-H
Do the following in Namespace default. Create a single Pod named ready-if-service-ready of image nginx:1.16.1-alpine. Configure a LivenessProbe which simply executes command true. Also configure a ReadinessProbe which does check if the url http://service-am-i-ready:80 is reachable, you can use wget -T2 -O- http://service-am-i-ready:80 for this. Start the Pod and confirm it isn’t ready because of the ReadinessProbe.
Create a second Pod named am-i-ready of image nginx:1.16.1-alpine with label id: cross-server-ready. The already existing Service service-am-i-ready should now have that second Pod as endpoint.
Now the first Pod should be in ready state, confirm that.
t’s a bit of an anti-pattern for one Pod to check another Pod for being ready using probes, hence the normally available readinessProbe.httpGet doesn’t work for absolute remote urls. Still the workaround requested in this task should show how probes and Pod<->Service communication works.
First we create the first Pod:
k run ready-if-service-ready –image=nginx:1.16.1-alpine $do > 4_pod1.yaml
vim 4_pod1.yaml
Next perform the necessary additions manually:
4_pod1.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: ready-if-service-ready
name: ready-if-service-ready
spec:
containers:
- image: nginx:1.16.1-alpine
name: ready-if-service-ready
resources: {}
livenessProbe: # add from here
exec:
command:
- ‘true’
readinessProbe:
exec:
command:
- sh
- -c
- ‘wget -T2 -O- http://service-am-i-ready:80’ # to here
dnsPolicy: ClusterFirst
restartPolicy: Always
status: {}
Then create the Pod:
k -f 4_pod1.yaml create
And confirm it’s in a non-ready state:
➜ k get pod ready-if-service-ready
NAME READY STATUS RESTARTS AGE
ready-if-service-ready 0/1 Running 0 7s
We can also check the reason for this using describe:
➜ k describe pod ready-if-service-ready
…
Warning Unhealthy 18s kubelet, cluster1-node1 Readiness probe failed: Connecting to service-am-i-ready:80 (10.109.194.234:80)
wget: download timed out
Now we create the second Pod:
k run am-i-ready –image=nginx:1.16.1-alpine –labels=”id=cross-server-ready”
The already existing Service service-am-i-ready should now have an Endpoint:
k describe svc service-am-i-ready
k get ep # also possible
Which will result in our first Pod being ready, just give it a minute for the Readiness probe to check again:
➜ k get pod ready-if-service-ready
NAME READY STATUS RESTARTS AGE
ready-if-service-ready 1/1 Running 0 53s
Look at these Pods coworking together!
Use context: kubectl config use-context k8s-c1-H
There are various Pods in all namespaces. Write a command into /opt/course/5/find_pods.sh which lists all Pods sorted by their AGE (metadata.creationTimestamp).
Write a second command into /opt/course/5/find_pods_uid.sh which lists all Pods sorted by field metadata.uid. Use kubectl sorting for both commands.
A good resources here (and for many other things) is the kubectl-cheat-sheet. You can reach it fast when searching for “cheat sheet” in the Kubernetes docs.
/opt/course/5/find_pods.sh
kubectl get pod -A –sort-by=.metadata.creationTimestamp
And to execute:
➜ sh /opt/course/5/find_pods.sh
NAMESPACE NAME … AGE
kube-system kube-scheduler-cluster1-controlplane1 … 63m
kube-system etcd-cluster1-controlplane1 … 63m
kube-system kube-apiserver-cluster1-controlplane1 … 63m
kube-system kube-controller-manager-cluster1-controlplane1 … 63m
…
For the second command:
/opt/course/5/find_pods_uid.sh
kubectl get pod -A –sort-by=.metadata.uid
And to execute:
➜ sh /opt/course/5/find_pods_uid.sh
NAMESPACE NAME … AGE
kube-system coredns-5644d7b6d9-vwm7g … 68m
project-c13 c13-3cc-runner-heavy-5486d76dd4-ddvlt … 63m
project-hamster web-hamster-shop-849966f479-278vp … 63m
project-c13 c13-3cc-web-646b6c8756-qsg4b … 63m
Use context: kubectl config use-context k8s-c1-H
Create a new PersistentVolume named safari-pv. It should have a capacity of 2Gi, accessMode ReadWriteOnce, hostPath /Volumes/Data and no storageClassName defined.
Next create a new PersistentVolumeClaim in Namespace project-tiger named safari-pvc . It should request 2Gi storage, accessMode ReadWriteOnce and should not define a storageClassName. The PVC should bound to the PV correctly.
Finally create a new Deployment safari in Namespace project-tiger which mounts that volume at /tmp/safari-data. The Pods of that Deployment should be of image httpd:2.4.41-alpine.
Answer
➜ vim 6_pv.yaml
Find an example from https://kubernetes.io/docs and alter it:
6_pv.yaml
kind: PersistentVolume
apiVersion: v1
metadata:
name: safari-pv
spec:
capacity:
storage: 2Gi
accessModes:
- ReadWriteOnce
hostPath:
path: “/Volumes/Data”
Then create it:
➜ k -f 6_pv.yaml create
Next the PersistentVolumeClaim:
➜ vim 6_pvc.yaml
Find an example from https://kubernetes.io/docs and alter it:
6_pvc.yaml
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
name: safari-pvc
namespace: project-tiger
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 2Gi
Then create:
➜ k -f 6_pvc.yaml create
And check that both have the status Bound:
➜ k -n project-tiger get pv,pvc
NAME CAPACITY … STATUS CLAIM …
persistentvolume/safari-pv 2Gi … Bound project-tiger/safari-pvc …
NAME STATUS VOLUME CAPACITY …
persistentvolumeclaim/safari-pvc Bound safari-pv 2Gi …
Next we create a Deployment and mount that volume:
➜ k -n project-tiger create deploy safari \
–image=httpd:2.4.41-alpine $do > 6_dep.yaml
➜ vim 6_dep.yaml
Alter the yaml to mount the volume:
6_dep.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
creationTimestamp: null
labels:
app: safari
name: safari
namespace: project-tiger
spec:
replicas: 1
selector:
matchLabels:
app: safari
strategy: {}
template:
metadata:
creationTimestamp: null
labels:
app: safari
spec:
volumes: # add
- name: data # add
persistentVolumeClaim: # add
claimName: safari-pvc # add
containers:
- image: httpd:2.4.41-alpine
name: container
volumeMounts: # add
- name: data # add
mountPath: /tmp/safari-data # add
➜ k -f 6_dep.yaml create
We can confirm it’s mounting correctly:
➜ k -n project-tiger describe pod safari-5cbf46d6d-mjhsb | grep -A2 Mounts:
Mounts:
/tmp/safari-data from data (rw) # there it is
/var/run/secrets/kubernetes.io/serviceaccount from default-token-n2sjj (ro)
Use context: kubectl config use-context k8s-c1-H
The metrics-server has been installed in the cluster. Your college would like to know the kubectl commands to:
show Nodes resource usage
show Pods and their containers resource usage
Please write the commands into /opt/course/7/node.sh and /opt/course/7/pod.sh.
Answer:
The command we need to use here is top:
➜ k top -h
Display Resource (CPU/Memory/Storage) usage.
The top command allows you to see the resource consumption for nodes or pods.
This command requires Metrics Server to be correctly configured and working on the server.
Available Commands:
node Display Resource (CPU/Memory/Storage) usage of nodes
pod Display Resource (CPU/Memory/Storage) usage of pods
We see that the metrics server provides information about resource usage:
➜ k top node
NAME CPU(cores) CPU% MEMORY(bytes) MEMORY%
cluster1-controlplane1 178m 8% 1091Mi 57%
cluster1-node1 66m 6% 834Mi 44%
cluster1-node2 91m 9% 791Mi 41%
We create the first file:
/opt/course/7/node.sh
kubectl top node
For the second file we might need to check the docs again:
➜ k top pod -h
Display Resource (CPU/Memory/Storage) usage of pods.
…
Namespace in current context is ignored even if specified with –namespace.
–containers=false: If present, print usage of containers within a pod.
–no-headers=false: If present, print output without headers.
…
With this we can finish this task:
/opt/course/7/pod.sh
kubectl top pod –containers=true
Use context: kubectl config use-context k8s-c1-H
Ssh into the controlplane node with ssh cluster1-controlplane1. Check how the controlplane components kubelet, kube-apiserver, kube-scheduler, kube-controller-manager and etcd are started/installed on the controlplane node. Also find out the name of the DNS application and how it’s started/installed on the controlplane node.
Write your findings into file /opt/course/8/controlplane-components.txt. The file should be structured like:
/opt/course/8/controlplane-components.txt
kubelet: [TYPE]
kube-apiserver: [TYPE]
kube-scheduler: [TYPE]
kube-controller-manager: [TYPE]
etcd: [TYPE]
dns: [TYPE] [NAME]
Choices of [TYPE] are: not-installed, process, static-pod, pod
Answer:
We could start by finding processes of the requested components, especially the kubelet at first:
➜ ssh cluster1-controlplane1
root@cluster1-controlplane1:~# ps aux | grep kubelet # shows kubelet process
We can see which components are controlled via systemd looking at /etc/systemd/system directory:
➜ root@cluster1-controlplane1:~# find /etc/systemd/system/ | grep kube
/etc/systemd/system/kubelet.service.d
/etc/systemd/system/kubelet.service.d/10-kubeadm.conf
/etc/systemd/system/multi-user.target.wants/kubelet.service
➜ root@cluster1-controlplane1:~# find /etc/systemd/system/ | grep etcd
This shows kubelet is controlled via systemd, but no other service named kube nor etcd. It seems that this cluster has been setup using kubeadm, so we check in the default manifests directory:
➜ root@cluster1-controlplane1:~# find /etc/kubernetes/manifests/
/etc/kubernetes/manifests/
/etc/kubernetes/manifests/kube-controller-manager.yaml
/etc/kubernetes/manifests/etcd.yaml
/etc/kubernetes/manifests/kube-apiserver.yaml
/etc/kubernetes/manifests/kube-scheduler.yaml
(The kubelet could also have a different manifests directory specified via parameter –pod-manifest-path in it’s systemd startup config)
This means the main 4 controlplane services are setup as static Pods. Actually, let’s check all Pods running on in the kube-system Namespace on the controlplane node:
➜ root@cluster1-controlplane1:~# kubectl -n kube-system get pod -o wide | grep controlplane1
coredns-5644d7b6d9-c4f68 1/1 Running … cluster1-controlplane1
coredns-5644d7b6d9-t84sc 1/1 Running … cluster1-controlplane1
etcd-cluster1-controlplane1 1/1 Running … cluster1-controlplane1
kube-apiserver-cluster1-controlplane1 1/1 Running … cluster1-controlplane1
kube-controller-manager-cluster1-controlplane1 1/1 Running … cluster1-controlplane1
kube-proxy-q955p 1/1 Running … cluster1-controlplane1
kube-scheduler-cluster1-controlplane1 1/1 Running … cluster1-controlplane1
weave-net-mwj47 2/2 Running … cluster1-controlplane1
There we see the 5 static pods, with -cluster1-controlplane1 as suffix.
We also see that the dns application seems to be coredns, but how is it controlled?
➜ root@cluster1-controlplane1$ kubectl -n kube-system get ds
NAME DESIRED CURRENT … NODE SELECTOR AGE
kube-proxy 3 3 … kubernetes.io/os=linux 155m
weave-net 3 3 … <none> 155m</none>
➜ root@cluster1-controlplane1$ kubectl -n kube-system get deploy
NAME READY UP-TO-DATE AVAILABLE AGE
coredns 2/2 2 2 155m
Seems like coredns is controlled via a Deployment. We combine our findings in the requested file:
/opt/course/8/controlplane-components.txt
kubelet: process
kube-apiserver: static-pod
kube-scheduler: static-pod
kube-controller-manager: static-pod
etcd: static-pod
dns: pod coredns
You should be comfortable investigating a running cluster, know different methods on how a cluster and its services can be setup and be able to troubleshoot and find error sources.
Use context: kubectl config use-context k8s-c2-AC
Ssh into the controlplane node with ssh cluster2-controlplane1. Temporarily stop the kube-scheduler, this means in a way that you can start it again afterwards.
Create a single Pod named manual-schedule of image httpd:2.4-alpine, confirm it’s created but not scheduled on any node.
Now you’re the scheduler and have all its power, manually schedule that Pod on node cluster2-controlplane1. Make sure it’s running.
Start the kube-scheduler again and confirm it’s running correctly by creating a second Pod named manual-schedule2 of image httpd:2.4-alpine and check if it’s running on cluster2-node1.
Answer:
Stop the Scheduler
First we find the controlplane node:
➜ k get node
NAME STATUS ROLES AGE VERSION
cluster2-controlplane1 Ready control-plane 26h v1.28.2
cluster2-node1 Ready <none> 26h v1.28.2
Then we connect and check if the scheduler is running:</none>
➜ ssh cluster2-controlplane1
➜ root@cluster2-controlplane1:~# kubectl -n kube-system get pod | grep schedule
kube-scheduler-cluster2-controlplane1 1/1 Running 0 6s
Kill the Scheduler (temporarily):
➜ root@cluster2-controlplane1:~# cd /etc/kubernetes/manifests/
➜ root@cluster2-controlplane1:~# mv kube-scheduler.yaml ..
And it should be stopped:
➜ root@cluster2-controlplane1:~# kubectl -n kube-system get pod | grep schedule
➜ root@cluster2-controlplane1:~#
Create a Pod
Now we create the Pod:
k run manual-schedule –image=httpd:2.4-alpine
And confirm it has no node assigned:
➜ k get pod manual-schedule -o wide
NAME READY STATUS … NODE NOMINATED NODE
manual-schedule 0/1 Pending … <none> <none></none></none>
Manually schedule the Pod
Let’s play the scheduler now:
k get pod manual-schedule -o yaml > 9.yaml
# 9.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: “2020-09-04T15:51:02Z”
labels:
run: manual-schedule
managedFields:
…
manager: kubectl-run
operation: Update
time: “2020-09-04T15:51:02Z”
name: manual-schedule
namespace: default
resourceVersion: “3515”
selfLink: /api/v1/namespaces/default/pods/manual-schedule
uid: 8e9d2532-4779-4e63-b5af-feb82c74a935
spec:
nodeName: cluster2-controlplane1 # add the controlplane node name
containers:
- image: httpd:2.4-alpine
imagePullPolicy: IfNotPresent
name: manual-schedule
resources: {}
terminationMessagePath: /dev/termination-log
terminationMessagePolicy: File
volumeMounts:
- mountPath: /var/run/secrets/kubernetes.io/serviceaccount
name: default-token-nxnc7
readOnly: true
dnsPolicy: ClusterFirst
…
The only thing a scheduler does, is that it sets the nodeName for a Pod declaration. How it finds the correct node to schedule on, that’s a very much complicated matter and takes many variables into account.
As we cannot kubectl apply or kubectl edit , in this case we need to delete and create or replace:
k -f 9.yaml replace –force
How does it look?
➜ k get pod manual-schedule -o wide
NAME READY STATUS … NODE
manual-schedule 1/1 Running … cluster2-controlplane1
It looks like our Pod is running on the controlplane now as requested, although no tolerations were specified. Only the scheduler takes tains/tolerations/affinity into account when finding the correct node name. That’s why it’s still possible to assign Pods manually directly to a controlplane node and skip the scheduler.
Start the scheduler again
➜ ssh cluster2-controlplane1
➜ root@cluster2-controlplane1:~# cd /etc/kubernetes/manifests/
➜ root@cluster2-controlplane1:~# mv ../kube-scheduler.yaml .
Checks it’s running:
➜ root@cluster2-controlplane1:~# kubectl -n kube-system get pod | grep schedule
kube-scheduler-cluster2-controlplane1 1/1 Running 0 16s
Schedule a second test Pod:
k run manual-schedule2 –image=httpd:2.4-alpine
➜ k get pod -o wide | grep schedule
manual-schedule 1/1 Running … cluster2-controlplane1
manual-schedule2 1/1 Running … cluster2-node1
Back to normal.
Use context: kubectl config use-context k8s-c1-H
Create a new ServiceAccount processor in Namespace project-hamster. Create a Role and RoleBinding, both named processor as well. These should allow the new SA to only create Secrets and ConfigMaps in that Namespace.
Answer:
Let’s talk a little about RBAC resources
A ClusterRole|Role defines a set of permissions and where it is available, in the whole cluster or just a single Namespace.
A ClusterRoleBinding|RoleBinding connects a set of permissions with an account and defines where it is applied, in the whole cluster or just a single Namespace.
Because of this there are 4 different RBAC combinations and 3 valid ones:
Role + RoleBinding (available in single Namespace, applied in single Namespace)
ClusterRole + ClusterRoleBinding (available cluster-wide, applied cluster-wide)
ClusterRole + RoleBinding (available cluster-wide, applied in single Namespace)
Role + ClusterRoleBinding (NOT POSSIBLE: available in single Namespace, applied cluster-wide)
To the solution
We first create the ServiceAccount:
➜ k -n project-hamster create sa processor
serviceaccount/processor created
Then for the Role:
k -n project-hamster create role -h # examples
So we execute:
k -n project-hamster create role processor \
–verb=create \
–resource=secret \
–resource=configmap
Which will create a Role like:
kubectl -n project-hamster create role processor –verb=create –resource=secret –resource=configmap
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
name: processor
namespace: project-hamster
rules:
- apiGroups:
- “”
resources:
- secrets
- configmaps
verbs:
- create
Now we bind the Role to the ServiceAccount:
k -n project-hamster create rolebinding -h # examples
So we create it:
k -n project-hamster create rolebinding processor \
–role processor \
–serviceaccount project-hamster:processor
This will create a RoleBinding like:
kubectl -n project-hamster create rolebinding processor –role processor –serviceaccount project-hamster:processor
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
name: processor
namespace: project-hamster
roleRef:
apiGroup: rbac.authorization.k8s.io
kind: Role
name: processor
subjects:
- kind: ServiceAccount
name: processor
namespace: project-hamster
To test our RBAC setup we can use kubectl auth can-i:
k auth can-i -h # examples
Like this:
➜ k -n project-hamster auth can-i create secret \
–as system:serviceaccount:project-hamster:processor
yes
➜ k -n project-hamster auth can-i create configmap \
–as system:serviceaccount:project-hamster:processor
yes
➜ k -n project-hamster auth can-i create pod \
–as system:serviceaccount:project-hamster:processor
no
➜ k -n project-hamster auth can-i delete secret \
–as system:serviceaccount:project-hamster:processor
no
➜ k -n project-hamster auth can-i get configmap \
–as system:serviceaccount:project-hamster:processor
no
Done.
Use context: kubectl config use-context k8s-c1-H
Use Namespace project-tiger for the following. Create a DaemonSet named ds-important with image httpd:2.4-alpine and labels id=ds-important and uuid=18426a0b-5f59-4e10-923f-c0e078e82462. The Pods it creates should request 10 millicore cpu and 10 mebibyte memory. The Pods of that DaemonSet should run on all nodes, also controlplanes.
Answer:
As of now we aren’t able to create a DaemonSet directly using kubectl, so we create a Deployment and just change it up:
k -n project-tiger create deployment –image=httpd:2.4-alpine ds-important $do > 11.yaml
vim 11.yaml
(Sure you could also search for a DaemonSet example yaml in the Kubernetes docs and alter it.)
Then we adjust the yaml to:
11.yaml
apiVersion: apps/v1
kind: DaemonSet # change from Deployment to Daemonset
metadata:
creationTimestamp: null
labels: # add
id: ds-important # add
uuid: 18426a0b-5f59-4e10-923f-c0e078e82462 # add
name: ds-important
namespace: project-tiger # important
spec:
#replicas: 1 # remove
selector:
matchLabels:
id: ds-important # add
uuid: 18426a0b-5f59-4e10-923f-c0e078e82462 # add
#strategy: {} # remove
template:
metadata:
creationTimestamp: null
labels:
id: ds-important # add
uuid: 18426a0b-5f59-4e10-923f-c0e078e82462 # add
spec:
containers:
- image: httpd:2.4-alpine
name: ds-important
resources:
requests: # add
cpu: 10m # add
memory: 10Mi # add
tolerations: # add
- effect: NoSchedule # add
key: node-role.kubernetes.io/control-plane # add
#status: {} # remove
It was requested that the DaemonSet runs on all nodes, so we need to specify the toleration for this.
Let’s confirm:
k -f 11.yaml create
➜ k -n project-tiger get ds
NAME DESIRED CURRENT READY UP-TO-DATE AVAILABLE NODE SELECTOR AGE
ds-important 3 3 3 3 3 <none> 8s
➜ k -n project-tiger get pod -l id=ds-important -o wide
NAME READY STATUS NODE
ds-important-6pvgm 1/1 Running ... cluster1-node1
ds-important-lh5ts 1/1 Running ... cluster1-controlplane1
ds-important-qhjcq 1/1 Running ... cluster1-node2</none>
Use context: kubectl config use-context k8s-c1-H
Use Namespace project-tiger for the following. Create a Deployment named deploy-important with label id=very-important (the Pods should also have this label) and 3 replicas. It should contain two containers, the first named container1 with image nginx:1.17.6-alpine and the second one named container2 with image google/pause.
There should be only ever one Pod of that Deployment running on one worker node. We have two worker nodes: cluster1-node1 and cluster1-node2. Because the Deployment has three replicas the result should be that on both nodes one Pod is running. The third Pod won’t be scheduled, unless a new worker node will be added.
In a way we kind of simulate the behaviour of a DaemonSet here, but using a Deployment and a fixed number of replicas.
Answer:
There are two possible ways, one using podAntiAffinity and one using topologySpreadConstraint.
PodAntiAffinity
The idea here is that we create a “Inter-pod anti-affinity” which allows us to say a Pod should only be scheduled on a node where another Pod of a specific label (here the same label) is not already running.
Let’s begin by creating the Deployment template:
k -n project-tiger create deployment \
–image=nginx:1.17.6-alpine deploy-important $do > 12.yaml
vim 12.yaml
Then change the yaml to:
12.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
creationTimestamp: null
labels:
id: very-important # change
name: deploy-important
namespace: project-tiger # important
spec:
replicas: 3 # change
selector:
matchLabels:
id: very-important # change
strategy: {}
template:
metadata:
creationTimestamp: null
labels:
id: very-important # change
spec:
containers:
- image: nginx:1.17.6-alpine
name: container1 # change
resources: {}
- image: google/pause # add
name: container2 # add
affinity: # add
podAntiAffinity: # add
requiredDuringSchedulingIgnoredDuringExecution: # add
- labelSelector: # add
matchExpressions: # add
- key: id # add
operator: In # add
values: # add
- very-important # add
topologyKey: kubernetes.io/hostname # add
status: {}
Specify a topologyKey, which is a pre-populated Kubernetes label, you can find this by describing a node.
TopologySpreadConstraints
We can achieve the same with topologySpreadConstraints. Best to try out and play with both.
12.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
creationTimestamp: null
labels:
id: very-important # change
name: deploy-important
namespace: project-tiger # important
spec:
replicas: 3 # change
selector:
matchLabels:
id: very-important # change
strategy: {}
template:
metadata:
creationTimestamp: null
labels:
id: very-important # change
spec:
containers:
- image: nginx:1.17.6-alpine
name: container1 # change
resources: {}
- image: google/pause # add
name: container2 # add
topologySpreadConstraints: # add
- maxSkew: 1 # add
topologyKey: kubernetes.io/hostname # add
whenUnsatisfiable: DoNotSchedule # add
labelSelector: # add
matchLabels: # add
id: very-important # add
status: {}
Apply and Run
Let’s run it:
k -f 12.yaml create
Then we check the Deployment status where it shows 2/3 ready count:
➜ k -n project-tiger get deploy -l id=very-important
NAME READY UP-TO-DATE AVAILABLE AGE
deploy-important 2/3 3 2 2m35s
And running the following we see one Pod on each worker node and one not scheduled.
➜ k -n project-tiger get pod -o wide -l id=very-important
NAME READY STATUS … NODE
deploy-important-58db9db6fc-9ljpw 2/2 Running … cluster1-node1
deploy-important-58db9db6fc-lnxdb 0/2 Pending … <none>
deploy-important-58db9db6fc-p2rz8 2/2 Running ... cluster1-node2
If we kubectl describe the Pod deploy-important-58db9db6fc-lnxdb it will show us the reason for not scheduling is our implemented podAntiAffinity ruling:</none>
Warning FailedScheduling 63s (x3 over 65s) default-scheduler 0/3 nodes are available: 1 node(s) had taint {node-role.kubernetes.io/control-plane: }, that the pod didn’t tolerate, 2 node(s) didn’t match pod affinity/anti-affinity, 2 node(s) didn’t satisfy existing pods anti-affinity rules.
Or our topologySpreadConstraints:
Warning FailedScheduling 16s default-scheduler 0/3 nodes are available: 1 node(s) had taint {node-role.kubernetes.io/control-plane: }, that the pod didn’t tolerate, 2 node(s) didn’t match pod topology spread constraints.
Use context: kubectl config use-context k8s-c1-H
Create a Pod named multi-container-playground in Namespace default with three containers, named c1, c2 and c3. There should be a volume attached to that Pod and mounted into every container, but the volume shouldn’t be persisted or shared with other Pods.
Container c1 should be of image nginx:1.17.6-alpine and have the name of the node where its Pod is running available as environment variable MY_NODE_NAME.
Container c2 should be of image busybox:1.31.1 and write the output of the date command every second in the shared volume into file date.log. You can use while true; do date»_space; /your/vol/path/date.log; sleep 1; done for this.
Container c3 should be of image busybox:1.31.1 and constantly send the content of file date.log from the shared volume to stdout. You can use tail -f /your/vol/path/date.log for this.
Check the logs of container c3 to confirm correct setup.
Answer:
First we create the Pod template:
k run multi-container-playground –image=nginx:1.17.6-alpine $do > 13.yaml
vim 13.yaml
And add the other containers and the commands they should execute:
13.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: multi-container-playground
name: multi-container-playground
spec:
containers:
- image: nginx:1.17.6-alpine
name: c1 # change
resources: {}
env: # add
- name: MY_NODE_NAME # add
valueFrom: # add
fieldRef: # add
fieldPath: spec.nodeName # add
volumeMounts: # add
- name: vol # add
mountPath: /vol # add
- image: busybox:1.31.1 # add
name: c2 # add
command: [“sh”, “-c”, “while true; do date»_space; /vol/date.log; sleep 1; done”] # add
volumeMounts: # add
- name: vol # add
mountPath: /vol # add
- image: busybox:1.31.1 # add
name: c3 # add
command: [“sh”, “-c”, “tail -f /vol/date.log”] # add
volumeMounts: # add
- name: vol # add
mountPath: /vol # add
dnsPolicy: ClusterFirst
restartPolicy: Always
volumes: # add
- name: vol # add
emptyDir: {} # add
status: {}
k -f 13.yaml create
Oh boy, lot’s of requested things. We check if everything is good with the Pod:
➜ k get pod multi-container-playground
NAME READY STATUS RESTARTS AGE
multi-container-playground 3/3 Running 0 95s
Good, then we check if container c1 has the requested node name as env variable:
➜ k exec multi-container-playground -c c1 – env | grep MY
MY_NODE_NAME=cluster1-node2
And finally we check the logging:
➜ k logs multi-container-playground -c c3
Sat Dec 7 16:05:10 UTC 2077
Sat Dec 7 16:05:11 UTC 2077
Sat Dec 7 16:05:12 UTC 2077
Sat Dec 7 16:05:13 UTC 2077
Sat Dec 7 16:05:14 UTC 2077
Sat Dec 7 16:05:15 UTC 2077
Sat Dec 7 16:05:16 UTC 2077
Use context: kubectl config use-context k8s-c1-H
You’re ask to find out following information about the cluster k8s-c1-H:
How many controlplane nodes are available?
How many worker nodes are available?
What is the Service CIDR?
Which Networking (or CNI Plugin) is configured and where is its config file?
Which suffix will static pods have that run on cluster1-node1?
Write your answers into file /opt/course/14/cluster-info, structured like this:
/opt/course/14/cluster-info
1: [ANSWER]
2: [ANSWER]
3: [ANSWER]
4: [ANSWER]
5: [ANSWER]
Answer:
How many controlplane and worker nodes are available?
➜ k get node
NAME STATUS ROLES AGE VERSION
cluster1-controlplane1 Ready control-plane 27h v1.28.2
cluster1-node1 Ready <none> 27h v1.28.2
cluster1-node2 Ready <none> 27h v1.28.2
We see one controlplane and two workers.</none></none>
What is the Service CIDR?
➜ ssh cluster1-controlplane1
➜ root@cluster1-controlplane1:~# cat /etc/kubernetes/manifests/kube-apiserver.yaml | grep range
- –service-cluster-ip-range=10.96.0.0/12
Which Networking (or CNI Plugin) is configured and where is its config file?
➜ root@cluster1-controlplane1:~# find /etc/cni/net.d/
/etc/cni/net.d/
/etc/cni/net.d/10-weave.conflist
➜ root@cluster1-controlplane1:~# cat /etc/cni/net.d/10-weave.conflist
{
“cniVersion”: “0.3.0”,
“name”: “weave”,
…
By default the kubelet looks into /etc/cni/net.d to discover the CNI plugins. This will be the same on every controlplane and worker nodes.
Which suffix will static pods have that run on cluster1-node1?
The suffix is the node hostname with a leading hyphen. It used to be -static in earlier Kubernetes versions.
Result
The resulting /opt/course/14/cluster-info could look like:
/opt/course/14/cluster-info
How many controlplane nodes are available?
1: 1
How many worker nodes are available?
2: 2
What is the Service CIDR?
3: 10.96.0.0/12
Which Networking (or CNI Plugin) is configured and where is its config file?
4: Weave, /etc/cni/net.d/10-weave.conflist
Which suffix will static pods have that run on cluster1-node1?
5: -cluster1-node1
Use context: kubectl config use-context k8s-c2-AC
Write a command into /opt/course/15/cluster_events.sh which shows the latest events in the whole cluster, ordered by time (metadata.creationTimestamp). Use kubectl for it.
Now delete the kube-proxy Pod running on node cluster2-node1 and write the events this caused into /opt/course/15/pod_kill.log.
Finally kill the containerd container of the kube-proxy Pod on node cluster2-node1 and write the events into /opt/course/15/container_kill.log.
Do you notice differences in the events both actions caused?
Answer:
# /opt/course/15/cluster_events.sh
kubectl get events -A –sort-by=.metadata.creationTimestamp
Now we delete the kube-proxy Pod:
k -n kube-system get pod -o wide | grep proxy # find pod running on cluster2-node1
k -n kube-system delete pod kube-proxy-z64cg
Now check the events:
sh /opt/course/15/cluster_events.sh
Write the events the killing caused into /opt/course/15/pod_kill.log:
/opt/course/15/pod_kill.log
kube-system 9s Normal Killing pod/kube-proxy-jsv7t …
kube-system 3s Normal SuccessfulCreate daemonset/kube-proxy …
kube-system <unknown> Normal Scheduled pod/kube-proxy-m52sx ...
default 2s Normal Starting node/cluster2-node1 ...
kube-system 2s Normal Created pod/kube-proxy-m52sx ...
kube-system 2s Normal Pulled pod/kube-proxy-m52sx ...
kube-system 2s Normal Started pod/kube-proxy-m52sx ...
Finally we will try to provoke events by killing the container belonging to the container of the kube-proxy Pod:</unknown>
➜ ssh cluster2-node1
➜ root@cluster2-node1:~# crictl ps | grep kube-proxy
1e020b43c4423 36c4ebbc9d979 About an hour ago Running kube-proxy …
➜ root@cluster2-node1:~# crictl rm 1e020b43c4423
1e020b43c4423
➜ root@cluster2-node1:~# crictl ps | grep kube-proxy
0ae4245707910 36c4ebbc9d979 17 seconds ago Running kube-proxy …
We killed the main container (1e020b43c4423), but also noticed that a new container (0ae4245707910) was directly created. Thanks Kubernetes!
Now we see if this caused events again and we write those into the second file:
sh /opt/course/15/cluster_events.sh
# /opt/course/15/container_kill.log
kube-system 13s Normal Created pod/kube-proxy-m52sx …
kube-system 13s Normal Pulled pod/kube-proxy-m52sx …
kube-system 13s Normal Started pod/kube-proxy-m52sx …
Comparing the events we see that when we deleted the whole Pod there were more things to be done, hence more events. For example was the DaemonSet in the game to re-create the missing Pod. Where when we manually killed the main container of the Pod, the Pod would still exist but only its container needed to be re-created, hence less events.
Use context: kubectl config use-context k8s-c1-H
Write the names of all namespaced Kubernetes resources (like Pod, Secret, ConfigMap…) into /opt/course/16/resources.txt.
Find the project-* Namespace with the highest number of Roles defined in it and write its name and amount of Roles into /opt/course/16/crowded-namespace.txt.
Answer:
Namespace and Namespaces Resources
Now we can get a list of all resources like:
k api-resources # shows all
k api-resources -h # help always good
k api-resources –namespaced -o name > /opt/course/16/resources.txt
Which results in the file:
/opt/course/16/resources.txt
bindings
configmaps
endpoints
events
limitranges
persistentvolumeclaims
pods
podtemplates
replicationcontrollers
resourcequotas
secrets
serviceaccounts
services
controllerrevisions.apps
daemonsets.apps
deployments.apps
replicasets.apps
statefulsets.apps
localsubjectaccessreviews.authorization.k8s.io
horizontalpodautoscalers.autoscaling
cronjobs.batch
jobs.batch
leases.coordination.k8s.io
events.events.k8s.io
ingresses.extensions
ingresses.networking.k8s.io
networkpolicies.networking.k8s.io
poddisruptionbudgets.policy
rolebindings.rbac.authorization.k8s.io
roles.rbac.authorization.k8s.io
Namespace with most Roles
➜ k -n project-c13 get role –no-headers | wc -l
No resources found in project-c13 namespace.
0
➜ k -n project-c14 get role –no-headers | wc -l
300
➜ k -n project-hamster get role –no-headers | wc -l
No resources found in project-hamster namespace.
0
➜ k -n project-snake get role –no-headers | wc -l
No resources found in project-snake namespace.
0
➜ k -n project-tiger get role –no-headers | wc -l
No resources found in project-tiger namespace.
0
Finally we write the name and amount into the file:
/opt/course/16/crowded-namespace.txt
project-c14 with 300 resources
Use context: kubectl config use-context k8s-c1-H
In Namespace project-tiger create a Pod named tigers-reunite of image httpd:2.4.41-alpine with labels pod=container and container=pod. Find out on which node the Pod is scheduled. Ssh into that node and find the containerd container belonging to that Pod.
Using command crictl:
Write the ID of the container and the info.runtimeType into /opt/course/17/pod-container.txt
Write the logs of the container into /opt/course/17/pod-container.log
Answer:
First we create the Pod:
k -n project-tiger run tigers-reunite \
–image=httpd:2.4.41-alpine \
–labels “pod=container,container=pod”
Next we find out the node it’s scheduled on:
k -n project-tiger get pod -o wide
or fancy:
k -n project-tiger get pod tigers-reunite -o jsonpath=”{.spec.nodeName}”
Then we ssh into that node and and check the container info:
➜ ssh cluster1-node2
➜ root@cluster1-node2:~# crictl ps | grep tigers-reunite
b01edbe6f89ed 54b0995a63052 5 seconds ago Running tigers-reunite …
➜ root@cluster1-node2:~# crictl inspect b01edbe6f89ed | grep runtimeType
“runtimeType”: “io.containerd.runc.v2”,
Then we fill the requested file (on the main terminal):
/opt/course/17/pod-container.txt
b01edbe6f89ed io.containerd.runc.v2
Finally we write the container logs in the second file:
ssh cluster1-node2 ‘crictl logs b01edbe6f89ed’ &> /opt/course/17/pod-container.log
The &> in above’s command redirects both the standard output and standard error.
You could also simply run crictl logs on the node and copy the content manually, if it’s not a lot. The file should look like:
/opt/course/17/pod-container.log
AH00558: httpd: Could not reliably determine the server’s fully qualified domain name, using 10.44.0.37. Set the ‘ServerName’ directive globally to suppress this message
AH00558: httpd: Could not reliably determine the server’s fully qualified domain name, using 10.44.0.37. Set the ‘ServerName’ directive globally to suppress this message
[Mon Sep 13 13:32:18.555280 2021] [mpm_event:notice] [pid 1:tid 139929534545224] AH00489: Apache/2.4.41 (Unix) configured – resuming normal operations
[Mon Sep 13 13:32:18.555610 2021] [core:notice] [pid 1:tid 139929534545224] AH00094: Command line: ‘httpd -D FOREGROUND’
Use context: kubectl config use-context k8s-c3-CCC
There seems to be an issue with the kubelet not running on cluster3-node1. Fix it and confirm that cluster has node cluster3-node1 available in Ready state afterwards. You should be able to schedule a Pod on cluster3-node1 afterwards.
Write the reason of the issue into /opt/course/18/reason.txt.
Answer:
The procedure on tasks like these should be to check if the kubelet is running, if not start it, then check its logs and correct errors if there are some.
Always helpful to check if other clusters already have some of the components defined and running, so you can copy and use existing config files. Though in this case it might not need to be necessary.
Check node status:
➜ k get node
NAME STATUS ROLES AGE VERSION
cluster3-controlplane1 Ready control-plane 14d v1.28.2
cluster3-node1 NotReady <none> 14d v1.28.2
First we check if the kubelet is running:</none>
➜ ssh cluster3-node1
➜ root@cluster3-node1:~# ps aux | grep kubelet
root 29294 0.0 0.2 14856 1016 pts/0 S+ 11:30 0:00 grep –color=auto kubelet
Nope, so we check if it’s configured using systemd as service:
➜ root@cluster3-node1:~# service kubelet status
● kubelet.service - kubelet: The Kubernetes Node Agent
Loaded: loaded (/lib/systemd/system/kubelet.service; enabled; vendor preset: enabled)
Drop-In: /etc/systemd/system/kubelet.service.d
└─10-kubeadm.conf
Active: inactive (dead) since Sun 2019-12-08 11:30:06 UTC; 50min 52s ago
…
Yes, it’s configured as a service with config at /etc/systemd/system/kubelet.service.d/10-kubeadm.conf, but we see it’s inactive. Let’s try to start it:
➜ root@cluster3-node1:~# service kubelet start
➜ root@cluster3-node1:~# service kubelet status
● kubelet.service - kubelet: The Kubernetes Node Agent
Loaded: loaded (/lib/systemd/system/kubelet.service; enabled; vendor preset: enabled)
Drop-In: /etc/systemd/system/kubelet.service.d
└─10-kubeadm.conf
Active: activating (auto-restart) (Result: exit-code) since Thu 2020-04-30 22:03:10 UTC; 3s ago
Docs: https://kubernetes.io/docs/home/
Process: 5989 ExecStart=/usr/local/bin/kubelet $KUBELET_KUBECONFIG_ARGS $KUBELET_CONFIG_ARGS $KUBELET_KUBEADM_ARGS $KUBELET_EXTRA_ARGS (code=exited, status=203/EXEC)
Main PID: 5989 (code=exited, status=203/EXEC)
Apr 30 22:03:10 cluster3-node1 systemd[5989]: kubelet.service: Failed at step EXEC spawning /usr/local/bin/kubelet: No such file or directory
Apr 30 22:03:10 cluster3-node1 systemd[1]: kubelet.service: Main process exited, code=exited, status=203/EXEC
Apr 30 22:03:10 cluster3-node1 systemd[1]: kubelet.service: Failed with result ‘exit-code’.
We see it’s trying to execute /usr/local/bin/kubelet with some parameters defined in its service config file. A good way to find errors and get more logs is to run the command manually (usually also with its parameters).
➜ root@cluster3-node1:~# /usr/local/bin/kubelet
-bash: /usr/local/bin/kubelet: No such file or directory
➜ root@cluster3-node1:~# whereis kubelet
kubelet: /usr/bin/kubelet
Another way would be to see the extended logging of a service like using journalctl -u kubelet.
Well, there we have it, wrong path specified. Correct the path in file /etc/systemd/system/kubelet.service.d/10-kubeadm.conf and run:
vim /etc/systemd/system/kubelet.service.d/10-kubeadm.conf # fix
systemctl daemon-reload && systemctl restart kubelet
systemctl status kubelet # should now show running
Also the node should be available for the api server, give it a bit of time though:
➜ k get node
NAME STATUS ROLES AGE VERSION
cluster3-controlplane1 Ready control-plane 14d v1.28.2
cluster3-node1 Ready <none> 14d v1.28.2
Finally we write the reason into the file:</none>
/opt/course/18/reason.txt
wrong path to kubelet binary specified in service config
Use context: kubectl config use-context k8s-c3-CCC
Do the following in a new Namespace secret. Create a Pod named secret-pod of image busybox:1.31.1 which should keep running for some time.
There is an existing Secret located at /opt/course/19/secret1.yaml, create it in the Namespace secret and mount it readonly into the Pod at /tmp/secret1.
Create a new Secret in Namespace secret called secret2 which should contain user=user1 and pass=1234. These entries should be available inside the Pod’s container as environment variables APP_USER and APP_PASS.
Confirm everything is working.
Answer
First we create the Namespace and the requested Secrets in it:
k create ns secret
cp /opt/course/19/secret1.yaml 19_secret1.yaml
vim 19_secret1.yaml
We need to adjust the Namespace for that Secret:
19_secret1.yaml
apiVersion: v1
data:
halt: IyEgL2Jpbi9zaAo…
kind: Secret
metadata:
creationTimestamp: null
name: secret1
namespace: secret # change
k -f 19_secret1.yaml create
Next we create the second Secret:
k -n secret create secret generic secret2 –from-literal=user=user1 –from-literal=pass=1234
Now we create the Pod template:
k -n secret run secret-pod –image=busybox:1.31.1 $do – sh -c “sleep 5d” > 19.yaml
vim 19.yaml
Then make the necessary changes:
19.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: secret-pod
name: secret-pod
namespace: secret # add
spec:
containers:
- args:
- sh
- -c
- sleep 1d
image: busybox:1.31.1
name: secret-pod
resources: {}
env: # add
- name: APP_USER # add
valueFrom: # add
secretKeyRef: # add
name: secret2 # add
key: user # add
- name: APP_PASS # add
valueFrom: # add
secretKeyRef: # add
name: secret2 # add
key: pass # add
volumeMounts: # add
- name: secret1 # add
mountPath: /tmp/secret1 # add
readOnly: true # add
dnsPolicy: ClusterFirst
restartPolicy: Always
volumes: # add
- name: secret1 # add
secret: # add
secretName: secret1 # add
status: {}
It might not be necessary in current K8s versions to specify the readOnly: true because it’s the default setting anyways.
And execute:
k -f 19.yaml create
Finally we check if all is correct:
➜ k -n secret exec secret-pod – env | grep APP
APP_PASS=1234
APP_USER=user1
➜ k -n secret exec secret-pod – find /tmp/secret1
/tmp/secret1
/tmp/secret1/..data
/tmp/secret1/halt
/tmp/secret1/..2019_12_08_12_15_39.463036797
/tmp/secret1/..2019_12_08_12_15_39.463036797/halt
➜ k -n secret exec secret-pod – cat /tmp/secret1/halt
#! /bin/sh
### BEGIN INIT INFO
# Provides: halt
# Required-Start:
# Required-Stop:
# Default-Start:
# Default-Stop: 0
# Short-Description: Execute the halt command.
# Description:
…
All is good.
Use context: kubectl config use-context k8s-c3-CCC
Your coworker said node cluster3-node2 is running an older Kubernetes version and is not even part of the cluster. Update Kubernetes on that node to the exact version that’s running on cluster3-controlplane1. Then add this node to the cluster. Use kubeadm for this.
Answer:
Upgrade Kubernetes to cluster3-controlplane1 version
Search in the docs for kubeadm upgrade: https://kubernetes.io/docs/tasks/administer-cluster/kubeadm/kubeadm-upgrade
➜ k get node
NAME STATUS ROLES AGE VERSION
cluster3-controlplane1 Ready control-plane 22h v1.28.2
cluster3-node1 Ready <none> 22h v1.28.2
Controlplane node seems to be running Kubernetes 1.28.2. Node cluster3-node2 might not yet be part of the cluster depending on previous tasks.</none>
➜ ssh cluster3-node2
➜ root@cluster3-node2:~# kubeadm version
kubeadm version: &version.Info{Major:”1”, Minor:”27”, GitVersion:”v1.27.4”, GitCommit:”fa3d7990104d7c1f16943a67f11b154b71f6a132”, GitTreeState:”clean”, BuildDate:”2023-07-19T12:19:40Z”, GoVersion:”go1.20.6”, Compiler:”gc”, Platform:”linux/amd64”}
➜ root@cluster3-node2:~# kubectl version –short
Flag –short has been deprecated, and will be removed in the future. The –short output will become the default.
Client Version: v1.27.4
Kustomize Version: v5.0.1
The connection to the server localhost:8080 was refused - did you specify the right host or port?
➜ root@cluster3-node2:~# kubelet –version
Kubernetes v1.27.4
Here kubeadm is already installed in the wanted version, so we don’t need to install it. Hence we can run:
➜ root@cluster3-node2:~# kubeadm upgrade node
couldn’t create a Kubernetes client from file “/etc/kubernetes/kubelet.conf”: failed to load admin kubeconfig: open /etc/kubernetes/kubelet.conf: no such file or directory
To see the stack trace of this error execute with –v=5 or higher
This is usually the proper command to upgrade a node. But this error means that this node was never even initialised, so nothing to update here. This will be done later using kubeadm join. For now we can continue with kubelet and kubectl:
➜ root@cluster3-node2:~# apt update
Hit:1 http://ppa.launchpad.net/rmescandon/yq/ubuntu focal InRelease
Get:2 http://security.ubuntu.com/ubuntu focal-security InRelease [114 kB]
Hit:4 http://us.archive.ubuntu.com/ubuntu focal InRelease
Get:3 https://packages.cloud.google.com/apt kubernetes-xenial InRelease [8,993 B]
Get:5 http://us.archive.ubuntu.com/ubuntu focal-updates InRelease [114 kB]
Get:6 http://us.archive.ubuntu.com/ubuntu focal-backports InRelease [108 kB]
Get:7 http://us.archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages [2,851 kB]
Get:8 http://us.archive.ubuntu.com/ubuntu focal-updates/main i386 Packages [884 kB]
Get:9 http://us.archive.ubuntu.com/ubuntu focal-updates/universe amd64 Packages [1,117 kB]
Get:10 http://us.archive.ubuntu.com/ubuntu focal-updates/universe i386 Packages [748 kB]
Fetched 5,946 kB in 3s (2,063 kB/s)
Reading package lists… Done
Building dependency tree
Reading state information… Done
217 packages can be upgraded. Run ‘apt list –upgradable’ to see them.
➜ root@cluster3-node2:~# apt show kubectl -a | grep 1.28
…
Version: 1.28.2-00
Version: 1.28.1-00
Version: 1.28.0-00
➜ root@cluster3-node2:~# apt install kubectl=1.28.2-00 kubelet=1.28.2-00
…
Fetched 29.1 MB in 4s (7,547 kB/s)
(Reading database … 112527 files and directories currently installed.)
Preparing to unpack …/kubectl_1.28.2-00_amd64.deb …
Unpacking kubectl (1.28.2-00) over (1.27.4-00) …
dpkg: warning: downgrading kubelet from 1.27.4-00 to 1.28.2-00
Preparing to unpack …/kubelet_1.28.2-00_amd64.deb …
Unpacking kubelet (1.28.2-00) over (1.27.4-00) …
Setting up kubectl (1.28.2-00) …
Setting up kubelet (1.28.2-00) …
➜ root@cluster3-node2:~# kubelet –version
Kubernetes v1.28.2
Now we’re up to date with kubeadm, kubectl and kubelet. Restart the kubelet:
➜ root@cluster3-node2:~# service kubelet restart
➜ root@cluster3-node2:~# service kubelet status
● kubelet.service - kubelet: The Kubernetes Node Agent
Loaded: loaded (/lib/systemd/system/kubelet.service; enabled; vendor preset: enabled)
Drop-In: /etc/systemd/system/kubelet.service.d
└─10-kubeadm.conf
Active: activating (auto-restart) (Result: exit-code) since Fri 2023-09-22 14:37:37 UTC; 2s a>
Docs: https://kubernetes.io/docs/home/
Process: 34331 ExecStart=/usr/bin/kubelet $KUBELET_KUBECONFIG_ARGS $KUBELET_CONFIG_ARGS $KUBEL>
Main PID: 34331 (code=exited, status=1/FAILURE)
Sep 22 14:37:37 cluster3-node2 systemd[1]: kubelet.service: Main process exited, code=exited, stat>
Sep 22 14:37:37 cluster3-node2 systemd[1]: kubelet.service: Failed with result ‘exit-code’.
These errors occur because we still need to run kubeadm join to join the node into the cluster. Let’s do this in the next step.
Add cluster3-node2 to cluster
First we log into the controlplane1 and generate a new TLS bootstrap token, also printing out the join command:
➜ ssh cluster3-controlplane1
➜ root@cluster3-controlplane1:~# kubeadm token create –print-join-command
kubeadm join 192.168.100.31:6443 –token lyl4o0.vbkmv9rdph5qd660 –discovery-token-ca-cert-hash sha256:b0c94ccf935e27306ff24bce4b8f611c621509e80075105b3f25d296a94927ce
➜ root@cluster3-controlplane1:~# kubeadm token list
TOKEN TTL EXPIRES …
lyl4o0.vbkmv9rdph5qd660 23h 2023-09-23T14:38:12Z …
n4dkqj.hu52l46jfo4he61e <forever> <never> ...
s7cmex.ty1olulkuljju9am 18h 2023-09-23T09:34:20Z ...
We see the expiration of 23h for our token, we could adjust this by passing the ttl argument.</never></forever>
Next we connect again to cluster3-node2 and simply execute the join command:
➜ ssh cluster3-node2
➜ root@cluster3-node2:~# kubeadm join 192.168.100.31:6443 –token lyl4o0.vbkmv9rdph5qd660 –discovery-token-ca-cert-hash sha256:b0c94ccf935e27306ff24bce4b8f611c621509e80075105b3f25d296a94927ce
[preflight] Running pre-flight checks
[preflight] Reading configuration from the cluster…
[preflight] FYI: You can look at this config file with ‘kubectl -n kube-system get cm kubeadm-config -o yaml’
W0922 14:39:56.786605 34648 configset.go:177] error unmarshaling configuration schema.GroupVersionKind{Group:”kubeproxy.config.k8s.io”, Version:”v1alpha1”, Kind:”KubeProxyConfiguration”}: strict decoding error: unknown field “logging”
[kubelet-start] Writing kubelet configuration to file “/var/lib/kubelet/config.yaml”
[kubelet-start] Writing kubelet environment file with flags to file “/var/lib/kubelet/kubeadm-flags.env”
[kubelet-start] Starting the kubelet
[kubelet-start] Waiting for the kubelet to perform the TLS Bootstrap…
This node has joined the cluster:
* Certificate signing request was sent to apiserver and a response was received.
* The Kubelet was informed of the new secure connection details.
Run ‘kubectl get nodes’ on the control-plane to see this node join the cluster.
➜ root@cluster3-node2:~# service kubelet status
● kubelet.service - kubelet: The Kubernetes Node Agent
Loaded: loaded (/lib/systemd/system/kubelet.service; enabled; vendor preset: enabled)
Drop-In: /etc/systemd/system/kubelet.service.d
└─10-kubeadm.conf
Active: active (running) since Fri 2023-09-22 14:39:57 UTC; 14s ago
Docs: https://kubernetes.io/docs/home/
Main PID: 34695 (kubelet)
Tasks: 12 (limit: 462)
Memory: 55.4M
…
If you have troubles with kubeadm join you might need to run kubeadm reset.
This looks great though for us. Finally we head back to the main terminal and check the node status:
➜ k get node
NAME STATUS ROLES AGE VERSION
cluster3-controlplane1 Ready control-plane 102m v1.28.2
cluster3-node1 Ready <none> 97m v1.28.2
cluster3-node2 NotReady <none> 108s v1.28.2
Give it a bit of time till the node is ready.</none></none>
➜ k get node
NAME STATUS ROLES AGE VERSION
cluster3-controlplane1 Ready control-plane 102m v1.28.2
cluster3-node1 Ready <none> 97m v1.28.2
cluster3-node2 Ready <none> 108s v1.28.2
We see cluster3-node2 is now available and up to date.</none></none>
Use context: kubectl config use-context k8s-c3-CCC
Create a Static Pod named my-static-pod in Namespace default on cluster3-controlplane1. It should be of image nginx:1.16-alpine and have resource requests for 10m CPU and 20Mi memory.
Then create a NodePort Service named static-pod-service which exposes that static Pod on port 80 and check if it has Endpoints and if it’s reachable through the cluster3-controlplane1 internal IP address. You can connect to the internal node IPs from your main terminal.
Answer:
➜ ssh cluster3-controlplane1
➜ root@cluster1-controlplane1:~# cd /etc/kubernetes/manifests/
➜ root@cluster1-controlplane1:~# kubectl run my-static-pod \
–image=nginx:1.16-alpine \
-o yaml –dry-run=client > my-static-pod.yaml
Then edit the my-static-pod.yaml to add the requested resource requests:
/etc/kubernetes/manifests/my-static-pod.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: my-static-pod
name: my-static-pod
spec:
containers:
- image: nginx:1.16-alpine
name: my-static-pod
resources:
requests:
cpu: 10m
memory: 20Mi
dnsPolicy: ClusterFirst
restartPolicy: Always
status: {}
And make sure it’s running:
➜ k get pod -A | grep my-static
NAMESPACE NAME READY STATUS … AGE
default my-static-pod-cluster3-controlplane1 1/1 Running … 22s
Now we expose that static Pod:
k expose pod my-static-pod-cluster3-controlplane1 \
–name static-pod-service \
–type=NodePort \
–port 80
This would generate a Service like:
kubectl expose pod my-static-pod-cluster3-controlplane1 –name static-pod-service –type=NodePort –port 80
apiVersion: v1
kind: Service
metadata:
creationTimestamp: null
labels:
run: my-static-pod
name: static-pod-service
spec:
ports:
- port: 80
protocol: TCP
targetPort: 80
selector:
run: my-static-pod
type: NodePort
status:
loadBalancer: {}
Then run and test:
➜ k get svc,ep -l run=my-static-pod
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/static-pod-service NodePort 10.99.168.252 <none> 80:30352/TCP 30s</none>
NAME ENDPOINTS AGE
endpoints/static-pod-service 10.32.0.4:80 30s
Looking good.
Use context: kubectl config use-context k8s-c2-AC
Check how long the kube-apiserver server certificate is valid on cluster2-controlplane1. Do this with openssl or cfssl. Write the exipiration date into /opt/course/22/expiration.
Also run the correct kubeadm command to list the expiration dates and confirm both methods show the same date.
Write the correct kubeadm command that would renew the apiserver server certificate into /opt/course/22/kubeadm-renew-certs.sh.
Answer:
First let’s find that certificate:
➜ ssh cluster2-controlplane1
➜ root@cluster2-controlplane1:~# find /etc/kubernetes/pki | grep apiserver
/etc/kubernetes/pki/apiserver.crt
/etc/kubernetes/pki/apiserver-etcd-client.crt
/etc/kubernetes/pki/apiserver-etcd-client.key
/etc/kubernetes/pki/apiserver-kubelet-client.crt
/etc/kubernetes/pki/apiserver.key
/etc/kubernetes/pki/apiserver-kubelet-client.key
Next we use openssl to find out the expiration date:
➜ root@cluster2-controlplane1:~# openssl x509 -noout -text -in /etc/kubernetes/pki/apiserver.crt | grep Validity -A2
Validity
Not Before: Dec 20 18:05:20 2022 GMT
Not After : Dec 20 18:05:20 2023 GMT
There we have it, so we write it in the required location on our main terminal:
/opt/course/22/expiration
Dec 20 18:05:20 2023 GMT
And we use the feature from kubeadm to get the expiration too:
➜ root@cluster2-controlplane1:~# kubeadm certs check-expiration | grep apiserver
apiserver Jan 14, 2022 18:49 UTC 363d ca no
apiserver-etcd-client Jan 14, 2022 18:49 UTC 363d etcd-ca no
apiserver-kubelet-client Jan 14, 2022 18:49 UTC 363d ca no
Looking good. And finally we write the command that would renew all certificates into the requested location:
/opt/course/22/kubeadm-renew-certs.sh
kubeadm certs renew apiserver
Use context: kubectl config use-context k8s-c2-AC
Node cluster2-node1 has been added to the cluster using kubeadm and TLS bootstrapping.
Find the “Issuer” and “Extended Key Usage” values of the cluster2-node1:
kubelet client certificate, the one used for outgoing connections to the kube-apiserver.
kubelet server certificate, the one used for incoming connections from the kube-apiserver.
Write the information into file /opt/course/23/certificate-info.txt.
Compare the “Issuer” and “Extended Key Usage” fields of both certificates and make sense of these.
Answer:
To find the correct kubelet certificate directory, we can look for the default value of the –cert-dir parameter for the kubelet. For this search for “kubelet” in the Kubernetes docs which will lead to: https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet. We can check if another certificate directory has been configured using ps aux or in /etc/systemd/system/kubelet.service.d/10-kubeadm.conf.
First we check the kubelet client certificate:
➜ ssh cluster2-node1
➜ root@cluster2-node1:~# openssl x509 -noout -text -in /var/lib/kubelet/pki/kubelet-client-current.pem | grep Issuer
Issuer: CN = kubernetes
➜ root@cluster2-node1:~# openssl x509 -noout -text -in /var/lib/kubelet/pki/kubelet-client-current.pem | grep “Extended Key Usage” -A1
X509v3 Extended Key Usage:
TLS Web Client Authentication
Next we check the kubelet server certificate:
➜ root@cluster2-node1:~# openssl x509 -noout -text -in /var/lib/kubelet/pki/kubelet.crt | grep Issuer
Issuer: CN = cluster2-node1-ca@1588186506
➜ root@cluster2-node1:~# openssl x509 -noout -text -in /var/lib/kubelet/pki/kubelet.crt | grep “Extended Key Usage” -A1
X509v3 Extended Key Usage:
TLS Web Server Authentication
We see that the server certificate was generated on the worker node itself and the client certificate was issued by the Kubernetes api. The “Extended Key Usage” also shows if it’s for client or server authentication.
More about this: https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet-tls-bootstrapping
Use context: kubectl config use-context k8s-c1-H
There was a security incident where an intruder was able to access the whole cluster from a single hacked backend Pod.
To prevent this create a NetworkPolicy called np-backend in Namespace project-snake. It should allow the backend-* Pods only to:
connect to db1-* Pods on port 1111
connect to db2-* Pods on port 2222
Use the app label of Pods in your policy.
After implementation, connections from backend-* Pods to vault-* Pods on port 3333 should for example no longer work.
Answer:
First we look at the existing Pods and their labels:
➜ k -n project-snake get pod
NAME READY STATUS RESTARTS AGE
backend-0 1/1 Running 0 8s
db1-0 1/1 Running 0 8s
db2-0 1/1 Running 0 10s
vault-0 1/1 Running 0 10s
➜ k -n project-snake get pod -L app
NAME READY STATUS RESTARTS AGE APP
backend-0 1/1 Running 0 3m15s backend
db1-0 1/1 Running 0 3m15s db1
db2-0 1/1 Running 0 3m17s db2
vault-0 1/1 Running 0 3m17s vault
We test the current connection situation and see nothing is restricted:
➜ k -n project-snake get pod -o wide
NAME READY STATUS RESTARTS AGE IP …
backend-0 1/1 Running 0 4m14s 10.44.0.24 …
db1-0 1/1 Running 0 4m14s 10.44.0.25 …
db2-0 1/1 Running 0 4m16s 10.44.0.23 …
vault-0 1/1 Running 0 4m16s 10.44.0.22 …
➜ k -n project-snake exec backend-0 – curl -s 10.44.0.25:1111
database one
➜ k -n project-snake exec backend-0 – curl -s 10.44.0.23:2222
database two
➜ k -n project-snake exec backend-0 – curl -s 10.44.0.22:3333
vault secret storage
Now we create the NP by copying and chaning an example from the k8s docs:
vim 24_np.yaml
# 24_np.yaml
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
name: np-backend
namespace: project-snake
spec:
podSelector:
matchLabels:
app: backend
policyTypes:
- Egress # policy is only about Egress
egress:
- # first rule
to: # first condition “to”
- podSelector:
matchLabels:
app: db1
ports: # second condition “port”
- protocol: TCP
port: 1111
- # second rule
to: # first condition “to”
- podSelector:
matchLabels:
app: db2
ports: # second condition “port”
- protocol: TCP
port: 2222
The NP above has two rules with two conditions each, it can be read as:
allow outgoing traffic if:
(destination pod has label app=db1 AND port is 1111)
OR
(destination pod has label app=db2 AND port is 2222)
Wrong example
Now let’s shortly look at a wrong example:
WRONG
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
name: np-backend
namespace: project-snake
spec:
podSelector:
matchLabels:
app: backend
policyTypes:
- Egress
egress:
- # first rule
to: # first condition “to”
- podSelector: # first “to” possibility
matchLabels:
app: db1
- podSelector: # second “to” possibility
matchLabels:
app: db2
ports: # second condition “ports”
- protocol: TCP # first “ports” possibility
port: 1111
- protocol: TCP # second “ports” possibility
port: 2222
The NP above has one rule with two conditions and two condition-entries each, it can be read as:
allow outgoing traffic if:
(destination pod has label app=db1 OR destination pod has label app=db2)
AND
(destination port is 1111 OR destination port is 2222)
Using this NP it would still be possible for backend-* Pods to connect to db2-* Pods on port 1111 for example which should be forbidden.
Create NetworkPolicy
We create the correct NP:
k -f 24_np.yaml create
And test again:
➜ k -n project-snake exec backend-0 – curl -s 10.44.0.25:1111
database one
➜ k -n project-snake exec backend-0 – curl -s 10.44.0.23:2222
database two
➜ k -n project-snake exec backend-0 – curl -s 10.44.0.22:3333
^C
Also helpful to use kubectl describe on the NP to see how k8s has interpreted the policy.
Great, looking more secure. Task done.
Use context: kubectl config use-context k8s-c3-CCC
Make a backup of etcd running on cluster3-controlplane1 and save it on the controlplane node at /tmp/etcd-backup.db.
Then create any kind of Pod in the cluster.
Finally restore the backup, confirm the cluster is still working and that the created Pod is no longer with us.
Answer:
Etcd Backup
First we log into the controlplane and try to create a snapshop of etcd:
➜ ssh cluster3-controlplane1
➜ root@cluster3-controlplane1:~# ETCDCTL_API=3 etcdctl snapshot save /tmp/etcd-backup.db
Error: rpc error: code = Unavailable desc = transport is closing
But it fails because we need to authenticate ourselves. For the necessary information we can check the etc manifest:
➜ root@cluster3-controlplane1:~# vim /etc/kubernetes/manifests/etcd.yaml
We only check the etcd.yaml for necessary information we don’t change it.
/etc/kubernetes/manifests/etcd.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
component: etcd
tier: control-plane
name: etcd
namespace: kube-system
spec:
containers:
- command:
- etcd
- –advertise-client-urls=https://192.168.100.31:2379
- –cert-file=/etc/kubernetes/pki/etcd/server.crt # use
- –client-cert-auth=true
- –data-dir=/var/lib/etcd
- –initial-advertise-peer-urls=https://192.168.100.31:2380
- –initial-cluster=cluster3-controlplane1=https://192.168.100.31:2380
- –key-file=/etc/kubernetes/pki/etcd/server.key # use
- –listen-client-urls=https://127.0.0.1:2379,https://192.168.100.31:2379 # use
- –listen-metrics-urls=http://127.0.0.1:2381
- –listen-peer-urls=https://192.168.100.31:2380
- –name=cluster3-controlplane1
- –peer-cert-file=/etc/kubernetes/pki/etcd/peer.crt
- –peer-client-cert-auth=true
- –peer-key-file=/etc/kubernetes/pki/etcd/peer.key
- –peer-trusted-ca-file=/etc/kubernetes/pki/etcd/ca.crt # use
- –snapshot-count=10000
- –trusted-ca-file=/etc/kubernetes/pki/etcd/ca.crt
image: k8s.gcr.io/etcd:3.3.15-0
imagePullPolicy: IfNotPresent
livenessProbe:
failureThreshold: 8
httpGet:
host: 127.0.0.1
path: /health
port: 2381
scheme: HTTP
initialDelaySeconds: 15
timeoutSeconds: 15
name: etcd
resources: {}
volumeMounts:
- mountPath: /var/lib/etcd
name: etcd-data
- mountPath: /etc/kubernetes/pki/etcd
name: etcd-certs
hostNetwork: true
priorityClassName: system-cluster-critical
volumes:
- hostPath:
path: /etc/kubernetes/pki/etcd
type: DirectoryOrCreate
name: etcd-certs
- hostPath:
path: /var/lib/etcd # important
type: DirectoryOrCreate
name: etcd-data
status: {}
But we also know that the api-server is connecting to etcd, so we can check how its manifest is configured:
➜ root@cluster3-controlplane1:~# cat /etc/kubernetes/manifests/kube-apiserver.yaml | grep etcd
- –etcd-cafile=/etc/kubernetes/pki/etcd/ca.crt
- –etcd-certfile=/etc/kubernetes/pki/apiserver-etcd-client.crt
- –etcd-keyfile=/etc/kubernetes/pki/apiserver-etcd-client.key
- –etcd-servers=https://127.0.0.1:2379
We use the authentication information and pass it to etcdctl:
➜ root@cluster3-controlplane1:~# ETCDCTL_API=3 etcdctl snapshot save /tmp/etcd-backup.db \
–cacert /etc/kubernetes/pki/etcd/ca.crt \
–cert /etc/kubernetes/pki/etcd/server.crt \
–key /etc/kubernetes/pki/etcd/server.key
Snapshot saved at /tmp/etcd-backup.db
NOTE: Dont use snapshot status because it can alter the snapshot file and render it invalid
Etcd restore
Now create a Pod in the cluster and wait for it to be running:
➜ root@cluster3-controlplane1:~# kubectl run test –image=nginx
pod/test created
➜ root@cluster3-controlplane1:~# kubectl get pod -l run=test -w
NAME READY STATUS RESTARTS AGE
test 1/1 Running 0 60s
NOTE: If you didn’t solve questions 18 or 20 and cluster3 doesn’t have a ready worker node then the created pod might stay in a Pending state. This is still ok for this task.
Next we stop all controlplane components:
root@cluster3-controlplane1:~# cd /etc/kubernetes/manifests/
root@cluster3-controlplane1:/etc/kubernetes/manifests# mv * ..
root@cluster3-controlplane1:/etc/kubernetes/manifests# watch crictl ps
Now we restore the snapshot into a specific directory:
➜ root@cluster3-controlplane1:~# ETCDCTL_API=3 etcdctl snapshot restore /tmp/etcd-backup.db \
–data-dir /var/lib/etcd-backup \
–cacert /etc/kubernetes/pki/etcd/ca.crt \
–cert /etc/kubernetes/pki/etcd/server.crt \
–key /etc/kubernetes/pki/etcd/server.key
2020-09-04 16:50:19.650804 I | mvcc: restore compact to 9935
2020-09-04 16:50:19.659095 I | etcdserver/membership: added member 8e9e05c52164694d [http://localhost:2380] to cluster cdf818194e3a8c32
We could specify another host to make the backup from by using etcdctl –endpoints http://IP, but here we just use the default value which is: http://127.0.0.1:2379,http://127.0.0.1:4001.
The restored files are located at the new folder /var/lib/etcd-backup, now we have to tell etcd to use that directory:
➜ root@cluster3-controlplane1:~# vim /etc/kubernetes/etcd.yaml
# /etc/kubernetes/etcd.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
component: etcd
tier: control-plane
name: etcd
namespace: kube-system
spec:
…
- mountPath: /etc/kubernetes/pki/etcd
name: etcd-certs
hostNetwork: true
priorityClassName: system-cluster-critical
volumes:
- hostPath:
path: /etc/kubernetes/pki/etcd
type: DirectoryOrCreate
name: etcd-certs
- hostPath:
path: /var/lib/etcd-backup # change
type: DirectoryOrCreate
name: etcd-data
status: {}
Now we move all controlplane yaml again into the manifest directory. Give it some time (up to several minutes) for etcd to restart and for the api-server to be reachable again:
root@cluster3-controlplane1:/etc/kubernetes/manifests# mv ../*.yaml .
root@cluster3-controlplane1:/etc/kubernetes/manifests# watch crictl ps
Then we check again for the Pod:
➜ root@cluster3-controlplane1:~# kubectl get pod -l run=test
No resources found in default namespace.
Awesome, backup and restore worked as our pod is gone.
