CKAD-journey

Kubernetes Container Health Probes - Quick Reference

Probe Types

Type	Purpose	When it runs	Failure Behavior
Startup Probe	Determines when app has initialized	During init phase only	Container restarts after failureThreshold
Liveness Probe	Detects if container is running correctly	Throughout lifecycle after startup	Container restarts
Readiness Probe	Checks if container can serve traffic	Throughout lifecycle	Container removed from service endpoints

Probe Mechanisms

Mechanism	How it works	Success criteria	Example
HTTP GET	Sends HTTP GET request	200-399 status code	httpGet: {path: "/healthz", port: 8080}
TCP Socket	Opens TCP connection	Connection established	tcpSocket: {port: 3306}
Exec	Runs command in container	Exit code 0	exec: {command: ["cat", "/tmp/healthy"]}

Common Parameters

Parameter	Description	Default	Example Value
initialDelaySeconds	Wait time after container starts	0	30
periodSeconds	How often to check	10	5
timeoutSeconds	How long to wait for response	1	3
successThreshold	Consecutive successes needed	1	1
failureThreshold	Consecutive failures before action	3	5

Quick Formulas

• Maximum startup time allowed = failureThreshold × periodSeconds
  • Example: 30 × 10 = 300 seconds (5 minutes)
• Probe frequency = Every periodSeconds seconds
  • Example: Every 5 seconds
• Time before first check = initialDelaySeconds after container starts
  • Example: 30 seconds after container starts

Common Pod Conditions

Condition	Meaning	Affected By
PodScheduled	Pod assigned to a node	Scheduler
Initialized	Init containers completed	Init container success
ContainersReady	All containers ready	Container readiness probes
Ready	Pod can serve traffic	Container readiness + readiness gates

Common YAML Snippets

HTTP Probe Example

livenessProbe:
  httpGet:
    path: /healthz
    port: 8080
  initialDelaySeconds: 15
  periodSeconds: 10
  timeoutSeconds: 3
  failureThreshold: 3

TCP Socket Probe Example

readinessProbe:
  tcpSocket:
    port: 3306
  initialDelaySeconds: 5
  periodSeconds: 10

Exec Probe Example

livenessProbe:
  exec:
    command:
    - cat
    - /tmp/healthy
  initialDelaySeconds: 5
  periodSeconds: 5

Startup Probe Example

startupProbe:
  httpGet:
    path: /healthz
    port: 8080
  failureThreshold: 30
  periodSeconds: 10

All Three Probes Together

startupProbe:
  httpGet:
    path: /startup
    port: 8080
  failureThreshold: 30
  periodSeconds: 10
livenessProbe:
  httpGet:
    path: /healthz
    port: 8080
  initialDelaySeconds: 10
  periodSeconds: 5
readinessProbe:
  httpGet:
    path: /ready
    port: 8080
  initialDelaySeconds: 5
  periodSeconds: 3

Readiness Gate Example

readinessGates:
- conditionType: "www.example.com/feature-1"

Essential Commands

# View pod status
kubectl get pods

# Check probe configuration
kubectl describe pod <pod-name>

# View detailed conditions
kubectl get pod <pod-name> -o json | jq '.status.conditions'

# Check container logs
kubectl logs <pod-name>

# Check events
kubectl get events --field-selector involvedObject.name=<pod-name>

# Test HTTP endpoint manually
kubectl exec <pod-name> -- curl -v http://localhost:8080/healthz

# Test TCP connection manually
kubectl exec <pod-name> -- nc -zv localhost 3306

# Create/remove file for exec probe testing
kubectl exec <pod-name> -- touch /tmp/healthy
kubectl exec <pod-name> -- rm /tmp/healthy

CKAD Exam Tips

1. Know these basic templates to save time during the exam
2. Use appropriate probe types:
   • Startup probes for slow-starting apps
   • Liveness probes for detecting crash/deadlock
   • Readiness probes for handling dependencies
3. Choose the right mechanism:
   • HTTP for web apps and APIs
   • TCP for databases and network services
   • Exec for custom checks and scripts
4. Set realistic timeouts:
   • Consider application’s normal response time
   • Be generous with initialDelaySeconds
5. Remember the defaults:
   • initialDelaySeconds: 0
   • periodSeconds: 10
   • timeoutSeconds: 1
   • successThreshold: 1
   • failureThreshold: 3