Trace the Complete Pod Lifecycle

# lifecycle-demo.yaml
cat << 'EOF' | kubectl apply -f -
apiVersion: v1
kind: Pod
metadata:
  name: lifecycle-demo
  namespace: default
  labels:
    demo: lifecycle
spec:
  initContainers:
  - name: init-check
    image: busybox:latest
    command: ['sh', '-c', 'echo "Init: checking dependencies"; sleep 2; echo "Init: done"']

  containers:
  - name: app
    image: nginx:1.25-alpine
    ports:
    - containerPort: 80

    resources:
      requests: {cpu: 50m, memory: 64Mi}
      limits:   {cpu: 200m, memory: 128Mi}

    lifecycle:
      postStart:
        exec:
          command: ["/bin/sh", "-c", "echo 'PostStart hook executed' >> /tmp/lifecycle.log"]
      preStop:
        exec:
          command: ["/bin/sh", "-c", "echo 'PreStop hook: draining connections'; sleep 5"]

    readinessProbe:
      httpGet:
        path: /
        port: 80
      initialDelaySeconds: 5
      periodSeconds: 5
      failureThreshold: 3

    livenessProbe:
      httpGet:
        path: /
        port: 80
      initialDelaySeconds: 15
      periodSeconds: 10
      failureThreshold: 3

    startupProbe:
      httpGet:
        path: /
        port: 80
      failureThreshold: 10
      periodSeconds: 3

  terminationGracePeriodSeconds: 30
EOF

# Watch phase and conditions
kubectl get pod lifecycle-demo -w

# Expected progression:
# lifecycle-demo   0/1   Pending             0   0s
# lifecycle-demo   0/1   Init:0/1            0   1s   ← init container
# lifecycle-demo   0/1   PodInitializing     0   5s   ← init done
# lifecycle-demo   0/1   Running             0   7s   ← container started
# lifecycle-demo   1/1   Running             0   12s  ← readiness passed

# Check which node the scheduler selected and why
kubectl describe pod lifecycle-demo | grep -A5 "Node:"

# View scheduler event
kubectl get events --field-selector \
  involvedObject.name=lifecycle-demo,reason=Scheduled

# See the node affinity, tolerations, and resource fit
kubectl describe pod lifecycle-demo | \
  grep -A20 "Conditions:" | head -20

# Example output:
# Conditions:
#   Type                 Status
#   Initialized          True    ← init containers done
#   Ready                True    ← readiness probe passed
#   ContainersReady      True
#   PodScheduled         True    ← scheduler assigned node

# Check postStart hook left its log entry
kubectl exec lifecycle-demo -- cat /tmp/lifecycle.log
# Expected: PostStart hook executed

# View all events in order
kubectl get events \
  --field-selector involvedObject.name=lifecycle-demo \
  --sort-by='.lastTimestamp' | head -20

# Events show full sequence:
# Scheduled, Pulling, Pulled, Created, Started

# Check probe configuration and current status
kubectl describe pod lifecycle-demo | \
  grep -A15 "Readiness:"

# Temporarily break readiness by changing the endpoint
kubectl exec lifecycle-demo -- \
  nginx -s stop 2>&1 || true
# nginx stops → readiness probe fails → pod marked not-ready

sleep 20
kubectl get pod lifecycle-demo
# READY column should show 0/1 after nginx stops

# Check the probe failure events
kubectl get events \
  --field-selector involvedObject.name=lifecycle-demo,reason=Unhealthy \
  --sort-by='.lastTimestamp'

# Start watching events before deleting
kubectl get events \
  --field-selector involvedObject.name=lifecycle-demo -w &

DELETE_START=$(date -u +%s)

# Delete the pod and observe the sequence
kubectl delete pod lifecycle-demo

# Expected event sequence:
# Killing  → preStop hook invoked
# (5 second sleep in preStop hook)
# Container terminated after SIGTERM

DELETE_END=$(date -u +%s)
echo "Deletion took: $((DELETE_END - DELETE_START))s"
# Should be ~5s (preStop) + SIGTERM handling time

# Re-create and wait for ready
kubectl apply -f lifecycle-demo.yaml
kubectl wait pod/lifecycle-demo --for=condition=Ready --timeout=60s

# View complete kubectl describe output with annotations
kubectl describe pod lifecycle-demo

# Key sections to understand:
# Node: ← where it's scheduled
# Start Time: ← when kubelet started working on it
# Labels/Annotations
# Status: Running
# IP: ← pod IP address
# Init Containers: ← init container status
# Containers: ← main container status + probe config
# Conditions: ← all True when healthy
# Volumes: ← projected service account token, etc.
# QoS Class: ← Burstable (requests != limits)
# Events: ← the lifecycle event log