1. What is Startup Probe?

👉 Startup probe = check if application has started successfully

• Runs only during startup (not continuous)
• Used for slow-starting apps (Java, Spring Boot, DB-heavy apps)
• Until it passes:
  • ❌ Liveness NOT executed
  • ❌ Readiness NOT executed

✅ This prevents Kubernetes from killing app too early.

2. Why we need Startup Probe (real problem)

Without startup probe:

• App takes 40 sec to start
• Liveness starts in 10 sec
  👉 Kubernetes thinks app failed
  👉 Restarts pod → CrashLoopBackOff

With startup probe:

• Kubernetes waits until app fully starts
• Then starts liveness & readiness

✅ Fixes unnecessary restarts

3. Three Main Differences (easy table)

Simple Startup Probe Example (YAML)

apiVersion: v1
kind: Pod
metadata:
  name: startup-demo
spec:
  containers:
  - name: app
    image: nginx
    ports:
    - containerPort: 80
    startupProbe:
      httpGet:
        path: /
        port: 80
      initialDelaySeconds: 5
      periodSeconds: 10
      failureThreshold: 5

What happens:

• Kubernetes sends HTTP request /
• If not ready → retry
• If fails many times → restart
• If success → ✅ start liveness & readiness

Another Example (Exec type – real usage)

startupProbe:
  exec:
    command:
    - cat
    - /tmp/app-ready
  initialDelaySeconds: 3
  periodSeconds: 5

Use case:

• App creates file /tmp/app-ready after startup
• Until then → probe fails
• Once file exists → app marked started

Commands (same as other probes)

kubectl apply -f startup.yaml
kubectl get pods
kubectl describe pod startup-demo

Real DevOps Example (important 🔥)

Scenario – Spring Boot app

• Startup time: 60 sec
• Without startup probe → killed repeatedly
• With startup probe → works fine

✅ This is VERY common issue in EKS / production

Short Explain:

Startup → app started or not

Liveness → app alive or not

Readiness → ready for traffic or not