What are Kubernetes Startup Probes?

Question

Accepted Answer

**Startup Probe** — startup check for slowly starting applications.

**Problem:** Liveness probe kills Pod before application has started (long initialization).

**Startup Probe solves this:**
```yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: slow-app
spec:
  template:
    spec:
      containers:
        - name: app
          image: my-slow-app:latest
          startupProbe:
            httpGet:
              path: /health
              port: 8080
            failureThreshold: 30
            periodSeconds: 10
            # 30 × 10 = 300 seconds max for startup
          readinessProbe:
            httpGet:
              path: /ready
              port: 8080
            periodSeconds: 5
          livenessProbe:
            httpGet:
              path: /health
              port: 8080
            periodSeconds: 10
```

**Check order:**
1. **Startup** → checked until it passes.
2. **Readiness** → checked after startup.
3. **Liveness** → checked after startup.

**While startup has not passed:**
- Liveness and readiness are NOT executed.
- Pod is not killed by liveness.
- Pod does not accept traffic (readiness = false).

**TCP Startup Probe:**
```yaml
startupProbe:
  tcpSocket:
    port: 8080
  failureThreshold: 30
  periodSeconds: 10
```

**Exec Startup Probe:**
```yaml
startupProbe:
  exec:
    command:
      - cat
      - /tmp/ready
  failureThreshold: 30
  periodSeconds: 10
```

**When to use:** Java/Spring Boot (long startup), ML model loading, DB migrations at startup.

DevOps: What are Kubernetes Startup Probes?