How to add multiple containers inside a single Pod template within a k8s Deployment manifest

You can have multiple containers inside a single Pod template within a Deployment manifest. This allows you to run tightly coupled applications together. The containers within a Pod share the same network namespace and can communicate with each other using localhost. They can also share storage volumes.

Here is an example of a Deployment manifest with multiple containers in a single Pod:

Example Deployment Manifest with Multiple Containers

apiVersion: apps/v1
kind: Deployment
metadata:
  name: multi-container-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: multi-container-app
  template:
    metadata:
      labels:
        app: multi-container-app
    spec:
      containers:
      - name: nginx-container
        image: nginx:latest
        ports:
        - containerPort: 80
      - name: sidecar-container
        image: busybox:latest
        command: ['sh', '-c', 'while true; do echo "Hello from the sidecar"; sleep 5; done']

Explanation:

• apiVersion: The version of the Kubernetes API to use.
• kind: The type of Kubernetes object. Here it is a Deployment.
• metadata: Metadata for the Deployment, including its name.
• spec: The specification of the Deployment.
  • replicas: The number of Pod replicas to run.
  • selector: Specifies how to identify the Pods that belong to this Deployment using labels.
  • template: The template for creating the Pods.
    • metadata: Metadata for the Pods, including labels.
    • spec: The specification for the Pods.
      • containers: A list of containers to run in each Pod.
        • name: The name of the container.
        • image: The Docker image for the container.
        • ports: The ports that the container exposes (optional).
        • command: The command to run inside the container (optional).

Use Case:

• nginx-container: Runs an NGINX web server.
• sidecar-container: Runs a BusyBox container that outputs a message every 5 seconds. This could represent a sidecar container for logging, monitoring, or other auxiliary tasks.

Apply the Deployment:

1. Save the YAML to a file, for example multi-container-deployment.yaml.

2. Apply the deployment to your Kubernetes cluster:

   kubectl apply -f multi-container-deployment.yaml
   

3. Verify the Deployment:

   kubectl get deployments
   

4. Inspect the Pods:

   kubectl get pods
   

5. Check the logs of each container:

   kubectl logs <pod-name> -c nginx-container
   kubectl logs <pod-name> -c sidecar-container