Init Containers in Kubernetes

 Question : There are some applications that need to be deployed on Kubernetes cluster and these apps have some pre-requisites where some configurations need to be changed before deploying the app container. Some of these changes cannot be made inside the images so the DevOps team has come up with a solution to use init containers to perform these tasks during deployment. Below is a sample scenario that the team is going to test first.

Create a Deployment named as ic-deploy-devops.

Configure spec as replicas should be 1, labels app should be ic-devops, template's metadata lables app should be the same ic-devops.

The initContainers should be named as ic-msg-devops, use image debian, preferably with latest tag and use command '/bin/bash', '-c' and 'echo Init Done - Welcome to xFusionCorp Industries > /ic/official'. The volume mount should be named as ic-volume-devops and mount path should be /ic.

Main container should be named as ic-main-devops, use image debian, preferably with latest tag and use command '/bin/bash', '-c' and 'while true; do cat /ic/official; sleep 5; done'. The volume mount should be named as ic-volume-devops and mount path should be /ic.

Volume to be named as ic-volume-devops and it should be an emptyDir type.

Note: The kubectl utility on jump_host has been configured to work with the kubernetes cluster.

Please Note:-  Perform the below commands based on your question server,  user name & other details that might differ. So please read the task carefully before executing it. 

All the Best 👍

Solution:  

1. Check existing running Pods  & Services 

thor@jump_host ~$ kubectl get pods No resources found in default namespace. thor@jump_host ~$ thor@jump_host ~$ kubectl get services NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE kubernetes   ClusterIP   10.96.0.1    <none>        443/TCP   13m thor@jump_host ~$ kubectl get deploy No resources found in default namespace. thor@jump_host ~$

2.  Create a YAML  file with all the parameters,  Kindly do the changes as per task

you can copy from GitLab    https://gitlab.com/nb-tech-support/devops.git

    ( Refer Below Video for more clarity )

thor@jump_host ~$ vi /tmp/init.yaml thor@jump_host ~$ cat /tmp/init.yaml apiVersion: apps/v1 kind: Deployment metadata:   name: ic-deploy-devops   labels:     app: ic-devops spec:   replicas: 1   selector:     matchLabels:       app: ic-devops   template:     metadata:       labels:         app: ic-devops     spec:       volumes:         - name: ic-volume-devops           emptyDir: {}       initContainers:         - name: ic-msg-devops           image: debian:latest           command:             [               "/bin/bash",               "-c",               "echo Init Done - Welcome to xFusionCorp Industries > /ic/official",             ]           volumeMounts:             - name: ic-volume-devops               mountPath: /ic         containers:         - name: ic-main-devops           image: debian:latest           command:             [               "/bin/bash",               "-c",               "while true; do cat /ic/official; sleep 5; done",             ]           volumeMounts:             - name: ic-volume-devops               mountPath: /ic thor@jump_host ~$

3. Run the below command to create a pod 

thor@jump_host ~$ kubectl create -f /tmp/init.yaml deployment.apps/ic-deploy-devops created thor@jump_host ~$

4.  Wait for the pod to get completed status

thor@jump_host ~$ kubectl get deploy NAME               READY   UP-TO-DATE   AVAILABLE   AGE ic-deploy-devops   0/1     1            0           23s thor@jump_host ~$ thor@jump_host ~$ kubectl get pods NAME                               READY   STATUS    RESTARTS   AGE ic-deploy-devops-59554f444-5dbmx   1/1     Running   0          29s thor@jump_host ~$

5.  Validate the task by logs & cat the file

thor@jump_host ~$ kubectl logs -f ic-deploy-devops-59554f444-5dbmx Init Done - Welcome to xFusionCorp Industries Init Done - Welcome to xFusionCorp Industries Init Done - Welcome to xFusionCorp Industries Init Done - Welcome to xFusionCorp Industries Init Done - Welcome to xFusionCorp Industries ^C thor@jump_host ~$ thor@jump_host ~$ kubectl exec ic-deploy-devops-59554f444-5dbmx -- cat /ic/official Init Done - Welcome to xFusionCorp Industries thor@jump_host ~$

6.  Click on Finish & Confirm to complete the task successfully

Happy Learning!!!!

Apart from this if you need more clarity,  I have made a  tutorial video on this, please go through and share your comments. Like and share the knowledge