DevOps: What is Kubernetes Pod Lifecycle Callback?

1apiVersion: apps/v1
2kind: Deployment
3metadata:
4  name: myapp
5spec:
6  replicas: 3
7  template:
8    spec:
9      terminationGracePeriodSeconds: 60
10      containers:
11      - name: app
12        image: myapp:latest
13        lifecycle:
14          postStart:
15            exec:
16              command:
17              - sh
18              - -c
19              - |
20                echo "Container started at $(date)" > /tmp/startup.log
21                wget -qO- http://config-server/config > /app/config
22                echo "Config loaded"
23          preStop:
24            exec:
25              command:
26              - sh
27              - -c
28              - |
29                # Drain connections
30                curl -X POST http://localhost:8080/admin/drain
31                # Wait for load balancer to remove
32                sleep 15
33                # Graceful shutdown
34                kill -TERM 1
35        startupProbe:
36          httpGet:
37            path: /healthz
38            port: 8080
39          failureThreshold: 30
40          periodSeconds: 10
41        readinessProbe:
42          httpGet:
43            path: /ready
44            port: 8080
45          initialDelaySeconds: 5
46          periodSeconds: 10
47        livenessProbe:
48          httpGet:
49            path: /healthz
50            port: 8080
51          initialDelaySeconds: 15
52          periodSeconds: 20

1# Check lifecycle hooks
2kubectl describe pod my-pod | grep -A 15 "Lifecycle"
3
4# View postStart logs
5kubectl logs my-pod -c app
6kubectl exec my-pod -- cat /tmp/startup.log
7
8# Check preStop execution
9kubectl get events --field-selector involvedObject.name=my-pod
10
11# Verify config was loaded
12kubectl exec my-pod -- cat /app/config
13
14# Test termination behavior
15kubectl delete pod my-pod && kubectl apply -f deployment.yaml