Pods & Deployments

Question 1

What’s a POD in kubernetes ?

Answer 1

The smallest deployable unit in the Kubernetes object model.

Question 2

Can we run container in kubernetes directly or outside the POD ?

Answer 2

No, containers always deployed within the POD.

Question 3

Which object in Kubernetes act as “environment” for containers ?

Answer 3

PODS

Question 4

Which properties of a POD are shared by containers within the POD?

Answer 4

Each container in a POD can share:
1. IP address
2. CPU
3. Memory
4. Storage

Question 5

Which object in Kubernetes is required to scale PODS horizontally ?

Answer 5

POD replica sets

Question 6

Does Kubernetes modifies/change a POD if it goes unhealthy ?

Answer 6

No, PODs are immutable. Kubernetes always replaces an un-healthy POD with healthy one, but never revives it.

Question 7

What are replicas ?

Answer 7

Replicas are copies or clones of a pod. It is the way to horizontally scale a POD.

Question 8

Does a sidecar container and main container within a POD can have same PORT ?

Answer 8

NO.
If there are more than one container inside a POD, then they must have different PORTS.

Question 9

What is one-container-per-pod approach ?

Answer 9

This says, each POD can contain only one container. This is the standard approach in any production environment.

Question 10

Can we span a single POD across nodes ?

Answer 10

NO.
A POD can only lie within a NODE due to limitation of IP address allocation.

Question 11

What is imperative vs declarative way of creating any resource in Kubernetes?

Answer 11

In “imperative” way, a programmer calls all the APIs exposed by the kubernetes to create and manage the resource.
In “declarative” way, a programmer just declare the state of the resource in an YAML and the rest is being done by Kubernetes.

Question 12

How to created a POD using imperative command?

Answer 12

> > > kubectl run [podName] –image=nginx:alpine

Question 13

What’s the command to show all pods running in cluster?

Answer 13

> > > kubectl get pods

Question 14

How to retrieve all resources running in a cluster?

Answer 14

> > > kubectl get all

Question 15

Can we access POD IP address outside the cluster ?

Answer 15

NO.
It is accessible within the cluster.

Question 16

How to access a POD’s port outside the cluster ?

Answer 16

> > > kubectl port-forward [podName] [external-port]:[internal-port]

Question 17

What is a YAML ?

Answer 17

YAML is just a text file with only Maps and Lists. It always uses “spaces” and No TABS.

Question 18

Can we create a key in YAML inside double quote ?

Answer 18

No, Key cannot be inside double quote

Question 19

What is the “casing” convention for “kind” values in Kubernetes manifests ?

Answer 19

The object Name must be started with “capital character”.

Question 20

Create a POD manifest.

Answer 20

> > > apiVersion: v1
kind: Pod
metadata:
name: nginx-pod
spec:
containers:
- name: nginx-pod
image: nginx:alpine

Question 21

What is the command to delete a pod ?

Answer 21

kubectl delete pod [pod-name]

Question 22

How to delete the pod, if we have created same via manifest file ?

Answer 22

kubectl delete -f file.pod.yml

Question 23

How to get inside a pod already running in the cluster ?

Answer 23

> > > kubectl exec [pod-name] -it sh

Question 24

What are Probes in kubernetes?

Answer 24

A Probe is nothing but the “diagnostic” performed periodically by “Kubelet”.

Question 25

What are the different types of Probes used by Kubernetes to determine the health of a container ?

Answer 25

1. Liveness Probe
2. Readiness Probe

Question 26

What’s a Liveness Probe ?

Answer 26

The Liveness Probe determines when should a container “restarts”

Question 27

What’s a Readiness Probe ?

Answer 27

The Readiness Prod determines when should a container starts receiving the traffic.

Question 28

How Kubernetes determines the health of a POD ?

Answer 28

By performing some actions on the POD. These actions can be:
1. ExecAction
2. TCPSocketAction
3. HTTPGetAction

Question 29

How kubernetes determines the health of a POD which is running only CLI based services ?

Answer 29

It runs a “ExecAction” on the POD.
If POD returns a “0” status, it means it is healthy.

Question 30

How kubernetes determines the health of a POD which is NOT running any service?

Answer 30

It can run a “TCPSocketAction” on the POD.
It checks against the container’s IP address against a PORT.

Question 31

How kubernetes determines the health of a POD which is running a REST service ?

Answer 31

It can run a “HTTPGetAction” on the POD.
If POD returns “200 ok”, it means it is healthy.

Question 32

What are the different status a PROBE can have ?

Answer 32

1. success
2. failure
3. unknown

Question 33

Where should we put the “liveness” or “readiness” probes configs in our Manifest file?

Answer 33

The Probes are part of “containers”. It should be provided in containers specification.

Question 34

Write manifest file with Readiness Probe.

Answer 34

apiVersion: v1
kind: Pod
metadata:
name: nginx-pod
spec:
containers:
- name: nginx-pod
image: nginx:alpine
readinessProbe:
httpGet:
path: /index.html
port: 80
initialDealySeconds: 2
periodSeconds: 5

Question 35

What does a POD do, if a underlying container fails?

Answer 35

It removes the container and create a new one. (restarts the container)