100-Days-Of-DevOps-Challenge-KodeKloud

Init Containers in Kubernetes

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 with latest tag and use command '/bin/bash', '-c' and 'echo Init Done - Welcome to xFusionCorp Industries > /ic/media'. 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 with latest tag and use command '/bin/bash', '-c' and 'while true; do cat /ic/media; 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.

Steps

1. Create the k3s-deployment.yaml using the content from this YAML file

2. Run deployment:

    kubectl apply -f k3s-deployment.yaml
   

3. Verify resuls:

    kubectl get deployments.apps
    kubectl get pods
   

Good to Know?

Init Containers

• Purpose: Run before main application containers
• Sequential Execution: Run one after another, not parallel
• Completion Required: Must complete successfully before main containers start
• Shared Resources: Share volumes and network with main containers

Use Cases

• Setup Tasks: Database schema creation, file downloads
• Dependency Checks: Wait for services to be available
• Configuration: Generate config files, set permissions
• Security: Fetch certificates, decrypt secrets

Init Container Behavior

• Restart Policy: Always restart on failure
• Resource Sharing: Share volumes with main containers
• Network: Same network namespace as main containers
• Failure Handling: Pod won’t start if init container fails

Best Practices

• Idempotent: Init containers should be safe to run multiple times
• Fast Execution: Keep init tasks quick to reduce startup time
• Error Handling: Proper error handling and logging
• Resource Limits: Set appropriate resource limits

This site is open source. Improve this page.