What is Kubernetes Pod Lifecycle and Graceful Shutdown?

Question

Accepted Answer

**Pod Lifecycle** — phases: Pending → Running → Succeeded/Failed.

**Graceful Shutdown (preStop hook + terminationGracePeriodSeconds):**
```yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  template:
    spec:
      terminationGracePeriodSeconds: 60
      containers:
        - name: myapp
          image: myapp:latest
          lifecycle:
            preStop:
              exec:
                command: ["/bin/sh", "-c", "sleep 15"]
          ports:
            - containerPort: 8080
          readinessProbe:
            httpGet:
              path: /health
              port: 8080
            initialDelaySeconds: 5
            periodSeconds: 10
```

**Shutdown order:**
1. Pod receives SIGTERM.
2. preStop hook executes.
3. Readiness probe becomes false (removed from Endpoints).
4. Application handles SIGTERM (closes connections).
5. If not completed within grace period → SIGKILL.

**Graceful shutdown example in Node.js:**
```typescript
const server = app.listen(8080);

const shutdown = () => {
  console.log("SIGTERM received, shutting down gracefully");
  server.close(() => {
    db.disconnect();
    process.exit(0);
  });

setTimeout(() => {
    process.exit(1);
  }, 30000);
};

process.on("SIGTERM", shutdown);
process.on("SIGINT", shutdown);
```

**PDB (Pod Disruption Budget):** Guarantees minimum available during voluntary disruptions.

**Pod Conditions:** PodScheduled, Initialized, ContainersReady, Ready.

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