Q-11 — Sidecar Logging (Final, Updated for Kubernetes v1.33 GA)

⭐ Kubernetes v1.33 — Official Sidecar Model (GA)

Starting from Kubernetes v1.33, the Native Sidecar Containers feature is GA (Generally Available). This means:

• Sidecars are no longer defined under containers:.
• Sidecars are defined under initContainers:.
• Sidecars use restartPolicy: Always.
• This causes the init container to run alongside the main container permanently, not just during startup.

Because the CKA exam environment runs on v1.33, this is now the expected and correct method for implementing sidecars.

The old (classic) pattern under containers: still works, but it is now considered legacy.

📌 Question Summary

A Deployment named synergy-deployment runs a main application container. The application writes logs to:

/var/log/synergy-deployment.log

You must:

1. Add a sidecar that continuously tails this log file.
2. Use image: busybox:stable.
3. Command:

tail -n+1 -f /var/log/synergy-deployment.log

✅ Native Sidecar Pattern (v1.33 GA) — Primary Solution

This is the correct approach for CKA 2025.

📍 Step-by-Step Solution

1. Edit the Deployment

kubectl edit deployment synergy-deployment

2. Add a shared volume at pod level

volumes:
  - name: logs
    emptyDir: {}

3. Mount the volume into the main container

volumeMounts:
  - name: logs
    mountPath: /var/log

4. Add the sidecar under initContainers with restartPolicy: Always

This is what transforms it into a native sidecar.

initContainers:
- name: sidecar
  image: busybox:stable
  restartPolicy: Always
  command: ["/bin/sh", "-c"]
  args:
    - tail -n+1 -f /var/log/synergy-deployment.log
  volumeMounts:
    - name: logs
      mountPath: /var/log

5. Save and allow rollout

Kubernetes will restart pods automatically.

6. Verify

kubectl get pods -l app=synergy
kubectl logs <pod> -c sidecar -f

You should see the live log stream.

🧾 Full Final Deployment Manifest (Native Sidecar, v1.33 GA)

apiVersion: apps/v1
kind: Deployment
metadata:
  name: synergy-deployment
  namespace: default
spec:
  replicas: 1
  selector:
    matchLabels:
      app: synergy
  template:
    metadata:
      labels:
        app: synergy
    spec:
      volumes:
      - name: logs
        emptyDir: {}

      initContainers:
      - name: sidecar
        image: busybox:stable
        restartPolicy: Always
        command: ["/bin/sh", "-c"]
        args:
          - tail -n+1 -f /var/log/synergy-deployment.log
        volumeMounts:
          - name: logs
            mountPath: /var/log

      containers:
      - name: legacy-app
        image: busybox:stable
        command: ["/bin/sh", "-c"]
        args:
          - |
            while true; do
              echo "$(date) - legacy app log entry" >> /var/log/synergy-deployment.log;
              sleep 5;
            done
        volumeMounts:
          - name: logs
            mountPath: /var/log

🟦 Legacy Pattern (For Reference Only)

Not recommended for CKA 2025, but included here for completeness.

Sidecar defined under containers::

containers:
- name: sidecar
  image: busybox:stable
  command: ["/bin/sh", "-c"]
  args:
    - tail -n+1 -f /var/log/synergy-deployment.log
  volumeMounts:
    - name: logs
      mountPath: /var/log

⚠️ Important Volume Handling Rules (Common Exam Traps)

These points MUST be remembered because this is where most students fail — and this is exactly what confused you in the exam.

✅ 1. If the Deployment already has a volume, you MUST reuse that same volume

• Do NOT create a new volume if one is already defined.
• Kubernetes questions often give an existing volume so you attach it to the sidecar + main container.
• Using a different or new volume would result in an empty directory → sidecar reads nothing.

Rule:

If a volume exists → reuse it.

✅ 2. If the Deployment has no existing volume, you MUST create one

• Use emptyDir: {} unless the question explicitly requires persistence.

• Mount it into BOTH:

• the main container (so it writes logs into the shared volume)

• the sidecar (so it can read the logs)

Rule:

If no volume exists → create one AND mount it in both containers.

✅ 3. Why BOTH containers must mount the volume

• Without mounting the volume in the main container, the main container writes logs to its own container filesystem.
• The sidecar would mount the volume, but the directory would be empty.
• Therefore, double-mounting is mandatory.

Rule:

A shared log file MUST come from a shared volume. Otherwise the sidecar cannot see it.

✅ 4. Where to write the volumeMounts in Native Sidecar Pattern

• Main container → under containers:
• Sidecar → under initContainers: with restartPolicy: Always
• Both mount the same path (e.g., /var/log).

🎯 Exam Strategy for CKA 2025

• ALWAYS use native sidecar pattern (initContainers + restartPolicy: Always).
• ONLY use the classic method if the question explicitly says: “Use a second container inside containers: to tail logs.”
• For all general sidecar tasks: Native Sidecar = Correct Answer.

controlplane ~ ➜  k get deploy
NAME                 READY   UP-TO-DATE   AVAILABLE   AGE
synergy-deployment   1/1     1            1           35m

controlplane ~ ➜  k edit deploy synergy-deployment -o yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  generation: 4
  name: synergy-deployment
  namespace: default
spec:
  replicas: 1
  selector:
    matchLabels:
      app: synergy
  strategy: {}
  template:
    metadata:
      labels:
        app: synergy
    spec:
      containers:
      - command:
        - sh
        - -c
        - tail -n+1 -f /var/log/synergy-deployment.log
        image: busybox
        name: sidecar
        volumeMounts:
        - mountPath: /var/log
          name: logs
      - args:
        - |
          while true; do
            echo "$(date) - legacy app log entry" >> /var/log/synergy-deployment.log;
            sleep 5;
          done
        command:
        - /bin/sh
        - -c
        image: busybox:stable
        name: legacy-app
        volumeMounts:
        - mountPath: /var/log
          name: logs
      restartPolicy: Always
      volumes:
      - emptyDir: {}
        name: logs

controlplane ~ ➜  k logs deployments/synergy-deployment -c sidecar
Sat Nov 15 20:08:39 UTC 2025 - legacy app log entry