DevOps: What is Kubernetes Pod Lifecycle Liveness Probe?

1apiVersion: apps/v1
2kind: Deployment
3metadata:
4  name: myapp
5spec:
6  replicas: 3
7  template:
8    spec:
9      containers:
10      - name: app
11        image: myapp:latest
12        livenessProbe:
13          httpGet:
14            path: /healthz
15            port: 8080
16            httpHeaders:
17            - name: X-Liveness
18              value: "check"
19          initialDelaySeconds: 15
20          periodSeconds: 20
21          timeoutSeconds: 5
22          successThreshold: 1
23          failureThreshold: 3
24---
25# TCP liveness probe
26apiVersion: apps/v1
27kind: Deployment
28metadata:
29  name: myapp-tcp
30spec:
31  template:
32    spec:
33      containers:
34      - name: app
35        image: myapp:latest
36        livenessProbe:
37          tcpSocket:
38            port: 8080
39          initialDelaySeconds: 15
40          periodSeconds: 20
41---
42# Exec liveness probe
43apiVersion: apps/v1
44kind: Deployment
45metadata:
46  name: myapp-exec
47spec:
48  template:
49    spec:
50      containers:
51      - name: app
52        image: myapp:latest
53        livenessProbe:
54          exec:
55            command:
56            - sh
57            - -c
58            - "pgrep myapp || exit 1"
59          initialDelaySeconds: 15
60          periodSeconds: 20

1# Check liveness probe
2kubectl describe pod my-pod | grep -A 10 "livenessProbe"
3
4# Check restart count
5kubectl get pod my-pod -o jsonpath='{.status.containerStatuses[0].restartCount}'
6
7# View liveness failures
8kubectl get events --field-selector reason=Unhealthy
9
10# Check probe logs
11kubectl logs my-pod --previous
12
13# Verify liveness endpoint
14kubectl exec my-pod -- curl -s http://localhost:8080/healthz