💡 Quick Answer: configuration

The Problem

This is a fundamental Kubernetes topic that engineers search for frequently. A comprehensive reference with production-ready examples saves hours of trial and error.

The Solution

The Three Probes

spec:
  containers:
    - name: app
      image: my-app:v1
      # Startup probe: wait for slow-starting apps
      startupProbe:
        httpGet:
          path: /healthz
          port: 8080
        failureThreshold: 30      # 30 × 10s = 5 min max startup
        periodSeconds: 10

      # Liveness probe: restart if dead
      livenessProbe:
        httpGet:
          path: /healthz
          port: 8080
        initialDelaySeconds: 0     # Startup probe handles the wait
        periodSeconds: 10
        failureThreshold: 3        # 3 failures = restart

      # Readiness probe: remove from Service if not ready
      readinessProbe:
        httpGet:
          path: /ready
          port: 8080
        periodSeconds: 5
        failureThreshold: 3

Anti-Patterns to AVOID

Anti-Pattern	Why It’s Bad	Fix
Liveness checks database	DB down → all pods restart → thundering herd	Only check app process health
Same endpoint for liveness + readiness	Can’t distinguish “dead” from “temporarily busy”	Separate `/healthz` and `/ready`
Too aggressive liveness (1s period, 1 failure)	Normal GC pauses trigger restarts	10s period, 3 failures
No startup probe for slow apps	Liveness kills pod before it starts	Add startupProbe
Readiness checks external deps	External service down → all pods unready → no traffic	Only check local readiness

Probe Types

# HTTP GET (most common)
livenessProbe:
  httpGet:
    path: /healthz
    port: 8080
    httpHeaders:
      - name: Accept
        value: application/json

# TCP Socket (databases, Redis)
livenessProbe:
  tcpSocket:
    port: 5432

# Exec command
livenessProbe:
  exec:
    command: ["pg_isready", "-U", "postgres"]

# gRPC (K8s 1.27+)
livenessProbe:
  grpc:
    port: 50051
    service: health.v1.Health

graph TD
    A[Pod starts] --> B{Startup probe}
    B -->|Passes| C[Liveness + Readiness probes start]
    B -->|Fails after threshold| D[Kill and restart pod]
    C --> E{Readiness probe}
    E -->|Pass| F[Added to Service endpoints]
    E -->|Fail| G[Removed from Service - no traffic]
    C --> H{Liveness probe}
    H -->|Pass| I[Pod stays running]
    H -->|Fail 3x| J[Container restarted]

Frequently Asked Questions

Do I need all three probes?

Readiness is almost always needed (controls traffic routing). Liveness is needed if your app can deadlock or hang. Startup is needed for slow-starting apps (Java, large model loading). Many apps only need readiness + liveness.

Best Practices

Start with the simplest configuration that meets your needs
Test changes in staging before production
Use kubectl describe and events for troubleshooting
Document your decisions for the team

Key Takeaways

This is essential Kubernetes knowledge for production operations
Follow the principle of least privilege and minimal configuration
Monitor and iterate based on real-world behavior
Automation reduces human error and improves consistency

Kubernetes Health Checks Best Practices