75.7 Project 37: Liveness and readiness probes

echo 'Probes tell kubelet when a container is alive and ready for traffic'

echo 'liveness restarts; readiness removes from Service Endpoints'

echo 'startupProbe protects slow apps from liveness kills during boot'

mkdir -p /tmp/k8s37 && printf '%s\n' 'apiVersion: apps/v1' 'kind: Deployment' 'metadata: {name: probe-demo}' 'spec:' '  replicas: 2' '  selector: {matchLabels: {app: probe-demo}}' '  template:' '    metadata: {labels: {app: probe-demo}}' '    spec:' '      containers:' '      - name: web' '        image: nginx:1.27-alpine' '        ports: [{containerPort: 80}]' '        readinessProbe:' '          httpGet: {path: /, port: 80}' '          initialDelaySeconds: 2' '          periodSeconds: 5' '        livenessProbe:' '          httpGet: {path: /, port: 80}' '          initialDelaySeconds: 10' '          periodSeconds: 10' > /tmp/k8s37/deploy.yaml && grep -E 'readinessProbe|livenessProbe' /tmp/k8s37/deploy.yaml

kubectl apply -f /tmp/k8s37/deploy.yaml

kubectl wait --for=condition=available deploy/probe-demo --timeout=90s

kubectl expose deploy probe-demo --port=80 --name=probe-demo 2>/dev/null || true; kubectl get endpoints probe-demo

kubectl get pods -l app=probe-demo -o jsonpath='{range .items[*]}{.metadata.name} {.status.containerStatuses[0].ready}{"\n"}{end}'

echo 'If readiness fails, Endpoints empty even while Pod Running'

kubectl get deploy probe-demo -o yaml | grep -A4 readinessProbe

kubectl get deploy probe-demo -o yaml | grep -A4 livenessProbe

echo 'Prefer httpGet for HTTP apps; use tcpSocket or exec when needed'

echo 'Break readiness: kubectl set probe by editing path to /not-real'

kubectl patch deploy probe-demo --type json -p '[{"op":"replace","path":"/spec/template/spec/containers/0/readinessProbe/httpGet/path","value":"/not-real"}]' && sleep 8; kubectl get endpoints probe-demo

kubectl get pods -l app=probe-demo

kubectl patch deploy probe-demo --type json -p '[{"op":"replace","path":"/spec/template/spec/containers/0/readinessProbe/httpGet/path","value":"/"}]' && kubectl rollout status deploy/probe-demo --timeout=90s

kubectl get endpoints probe-demo -o jsonpath='{.subsets[0].addresses[*].ip}' | wc -w

echo 'Never point liveness at a dependency like a database'

echo 'initialDelaySeconds gives boot time before first probe'

echo 'periodSeconds is how often kubelet probes'

echo 'failureThreshold times period equals roughly time-to-restart'

echo 'startupProbe with failureThreshold high protects slow JVMs'

echo 'Disable liveness until startupProbe succeeds when both are set'

echo 'exec probes must be cheap; heavy scripts hurt the node'

kubectl describe pod -l app=probe-demo | grep -E 'Readiness|Liveness|Restart' | head -10

kubectl get pods -l app=probe-demo -o jsonpath='{.items[0].status.containerStatuses[0].restartCount}'; echo

echo 'Rising restartCount with failing liveness means investigate logs'

kubectl logs -l app=probe-demo --tail=3

kubectl get events --field-selector reason=Unhealthy --sort-by=.lastTimestamp 2>/dev/null | tail -3 || echo 'no Unhealthy yet'

echo 'Tune probes in stage with real traffic shapes before prod'

kubectl get deploy probe-demo -o jsonpath='{.spec.template.spec.containers[0].readinessProbe.httpGet.path}'; echo

kubectl get deploy probe-demo -o jsonpath='{.spec.template.spec.containers[0].livenessProbe.periodSeconds}'; echo

echo 'Optional cleanup: kubectl delete deploy probe-demo svc probe-demo'

kubectl get endpoints probe-demo -o jsonpath='{.metadata.name}'; echo

kubectl get deploy probe-demo -o jsonpath='{.status.readyReplicas}'; echo

echo 'Neha: PASS'