Nodes

Question 1

What should be unique in a Node

Answer 1

Node name should be unique and we register with k8s with a unique node name. No 2 nodes can have the same node name

Question 2

What are the two ways you can register nodes with k8s apiserver

Answer 2

Self registration and manual registration

Question 3

What is required for a kubelet on a node to self register

Answer 3

kubeconfig to identify and authenticate to API server for registration. Flag –register-node set to true for automatically register the node.

Question 4

What is the flag –node-ip used for

Answer 4

It provides a list of ip address (v4 or v6) to contact the node. You can only register a single ip for each family for example only 1 per IPV4 and 1 for IPV6.

Question 5

What is the –node-labels used for

Answer 5

This will provide labels to assign to the node on registration.

Question 6

how can you ensure a node is added with certain taints that will stop it from running certain pods

Answer 6

use the flag –register-with-taints for self registration

Question 7

What is the best practice to change –node-labels for a node

Answer 7

It is always recommended to re-register the node to API server when changing node labels to avoid incorrect pod scheduling

Question 8

How can you find how much resources a node has

Answer 8

kubectl describe node will provide the capacity and allocatable

Question 9

Explain different conditions of the node

Answer 9

Ready - normal operating mode
Disk pressure - True if pressure on disk size meaning if the disk capacity goes low this will be set to True
Memory pressure - If node memory is low
PID pressure - if there are too many processes on the node
NetworkUnavaiable - If the network is not correctly configured

Question 10

How to use a different hostname for kubelet than what is configured in the node operating system

Answer 10

–host-name-override option can be used with kubelet.

Question 11

How long does the API server wait for before marking the node as unschedulable

Answer 11

node-monitor-grace-period which is 40 seconds by default

Question 12

What happens when a node is not reachable by the api server.

Answer 12

API server marks the node with taints based on the type of condition
Node is not reachable - Mark with taint node.kubernetes.io/unreachable for Unknown Status
Kubelet not responding - Mark node.kubernetes.io/not-ready taint

Question 13

What tain will cause the pods from a node to be evicted

Answer 13

NoExecute taint which is set will evict the pods that were running on the node

Question 14

Why daemonsets are not evicted when you cordon a node

Answer 14

Scheduler decides to evict pods based on the taints attached to the node, daemonset controller when scheduling a pod adds a bunch of tolerations to the pod such as node.kubernetes.io/unreachable:NoExecute etc… these tolerations will allow the pod to run even though the nodes have been tainted

Question 15

What is one of the field, the scheduler considers before scheduling a pod on a node

Answer 15

Scheduler looks for taints on the node to decide if the pod can be scheduled on the node.

Question 16

What is the default no. of pods that a node can run and how can you check that no.

Answer 16

node describe will show the Capacity which is 110 pods by default

Question 17

How do you find kubelet and kubeproxy version of a node

Answer 17

describe has it in Info column including kernel and containerd version

Question 18

How much of the resources are allocatable in a node

Answer 18

Allocatable = Capacity - Kube-reserved - system-reserved - eviction threshold

Question 19

Does kubelet enforce if pods use more than the allocatable

Answer 19

Kubelet can be configured to enforce allocatable limits with flag –enforce-node-allocatable flag, values are pods,system-reserved and kube-reserved

Question 20

What is the use of eviction threshold

Answer 20

If bad pods leak memory or storage it could cause the host OS to run out of resources and cause OOM which will affect all the pods and host OS for this purpose eviction thresholds can be defined in the kubelet which will evict pods when the threshold is hit. Flag name is –eviction-hard

Question 21

Show an example to evict pods when available memory on a node goes < 500Mi

Answer 21

–eviction-hard=memory.available<500Mi