Kubernetes Side Car Pattern

  🚗 What is the Sidecar Pattern? The Sidecar Pattern is a Kubernetes design pattern where two containers run in the same Pod and work to...

 

🚗 What is the Sidecar Pattern?

The Sidecar Pattern is a Kubernetes design pattern where two containers run in the same Pod and work together.

Think of it like:

🧑 Main app + 🛵 Sidekick (helper container)

They share the same network and storage space because they are in the same pod.

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🎯 Use Cases of Sidecar:

• Logging agents

• Monitoring agents

• Proxy services (like Envoy, Istio)

• Data sync or backup helpers

• File watchers or preprocessors

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📦 Simple Example: Nginx Web Server + Sidecar That Updates Content

We'll create a pod:

• nginx: serves web content.

• updater: a sidecar container that periodically updates the HTML file.

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🧾 Full YAML Example: nginx-sidecar-pod.yaml

yaml
apiVersion: v1
kind: Pod
metadata:
  name: nginx-with-sidecar
spec:
  volumes:
    - name: shared-data
      emptyDir: {}

  containers:
    - name: nginx
      image: nginx
      volumeMounts:
        - mountPath: /usr/share/nginx/html
          name: shared-data
      ports:
        - containerPort: 80

    - name: updater
      image: busybox
      command: ["/bin/sh", "-c"]
      args:
        - while true; do
            echo "Hello from Sidecar! Time: $(date)" > /shared/index.html;
            sleep 5;
          done
      volumeMounts:
        - mountPath: /shared
          name: shared-data

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🔍 Explanation:

Component	Purpose
nginx	Main container to serve the web content.
updater	Sidecar that writes new content every 5s.
shared-data	Shared volume so both containers can access /usr/share/nginx/html.

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⚙️ How It Works:

• updater writes a file: /shared/index.html → shared with nginx at /usr/share/nginx/html.

• nginx serves this file on port 80.

• Every 5 seconds, the file is updated with the current time.

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🔗 Test It

1. Apply the pod:

kubectl apply -f nginx-sidecar-pod.yaml

2. Port forward to access it locally:

kubectl port-forward pod/nginx-with-sidecar 8080:80

3. Open your browser:

http://localhost:8080

You'll see:

Hello from Sidecar! Time: <current time>

Which updates every 5 seconds. 🎉