What are Kubernetes Sidecar Containers (GA)?

Question

Accepted Answer

**Sidecar Containers (K8s 1.28+ GA)** — init containers with restartPolicy: Always.

**Problem:** Traditional sidecars (Envoy, Fluentd) — containers in Pod, but they do not restart on failure.

**Solution — native sidecar:**
```yaml
apiVersion: v1
kind: Pod
metadata:
  name: myapp
spec:
  initContainers:
    - name: envoy-sidecar
      image: envoyproxy/envoy:v1.28
      restartPolicy: Always  # GA in 1.28+
      ports:
        - containerPort: 15001
          name: inbound
        - containerPort: 15006
          name: outbound
    - name: log-shipper
      image: fluent/fluent-bit:latest
      restartPolicy: Always
      volumeMounts:
        - name: shared-logs
          mountPath: /var/log/app
  containers:
    - name: app
      image: myapp:latest
      volumeMounts:
        - name: shared-logs
          mountPath: /var/log/app
  volumes:
    - name: shared-logs
      emptyDir: {}
```

**Startup order:**
1. Init containers without restartPolicy (sequential).
2. Init containers with restartPolicy: Always (parallel with app).
3. App containers.

**Advantages:**
- Sidecar starts BEFORE app containers.
- Restarts on failure.
- Terminates AFTER app containers.

**Use cases:** Envoy proxy, log collectors, config watchers, monitoring agents.

DevOps: What are Kubernetes Sidecar Containers (GA)?