How to setup a logger sidecar container in Kubernetes

 We’ll set up:

• A main container (writes logs to a file).

• A sidecar container (reads the log and prints it to stdout).

• Deploy them together in a Pod.

• Run it inside Minikube.

⸻

🔹 1. Kubernetes Pod YAML (main + sidecar)

Save as pod-sidecar.yaml:

apiVersion: v1

kind: Pod

metadata:

  name: main-sidecar-pod

spec:

  containers:

  - name: main-app

    image: busybox

    command: ["/bin/sh", "-c"]

    args:

      - |

        while true; do

          echo "$(date) : Hello from MAIN container" >> /var/log/app.log;

          sleep 5;

        done

    volumeMounts:

    - name: shared-logs

      mountPath: /var/log

  - name: sidecar-log-reader

    image: busybox

    command: ["/bin/sh", "-c"]

    args:

      - |

        tail -n+1 -f /var/log/app.log

    volumeMounts:

    - name: shared-logs

      mountPath: /var/log

  volumes:

  - name: shared-logs

    emptyDir: {}

What this does:

• main-app writes a timestamped log to /var/log/app.log.

• sidecar-log-reader tails the same log file (via emptyDir shared volume).

• Both share the same directory /var/log.

⸻

🔹 2. Run on Minikube

Step 1: Start Minikube

minikube start

Step 2: Apply the Pod

kubectl apply -f pod-sidecar.yaml

Step 3: Verify the Pod

kubectl get pods

You should see:

main-sidecar-pod   Running   2/2   0   <time>

(2/2 containers means both main + sidecar are running.)

⸻

🔹 3. Check the logs

👉 Logs from sidecar (should continuously show main’s logs):

kubectl logs -f main-sidecar-pod -c sidecar-log-reader

👉 Logs from main (itself writes to file, not stdout):

kubectl exec -it main-sidecar-pod -c main-app -- tail -f /var/log/app.log

⸻

🔹 4. Clean up

kubectl delete pod main-sidecar-pod