# How-to: Scrivere Healthchecks Personalizzati

Come creare healthchecks custom per diversi tipi di servizi.

## Pattern Comuni

### HTTP Healthcheck

```yaml
healthcheck:
  test: ["CMD-SHELL", "curl -f http://localhost/health || exit 1"]
  interval: 15s
  timeout: 3s
  retries: 3
```

### TCP Port Check

```yaml
healthcheck:
  test: ["CMD-SHELL", "nc -z localhost 8080 || exit 1"]
  interval: 10s
  timeout: 2s
  retries: 3
```

### File Existence Check

```yaml
healthcheck:
  test: ["CMD-SHELL", "test -f /var/run/app/ready || exit 1"]
  interval: 5s
  timeout: 1s
  retries: 5
```

### Database Connection

```yaml
healthcheck:
  test: ["CMD-SHELL", "mysqladmin ping -h localhost || exit 1"]
  interval: 10s
  timeout: 5s
  retries: 5
```

### Redis Check

```yaml
healthcheck:
  test: ["CMD", "redis-cli", "ping"]
  interval: 10s
  timeout: 3s
  retries: 3
```

### Python Script Check

```yaml
healthcheck:
  test: ["CMD-SHELL", "python /app/healthcheck.py || exit 1"]
  interval: 30s
  timeout: 10s
  retries: 3
```

## Best Practices

### 1. Check Leggeri
```yaml
# ✓ GOOD - pagina leggera
test: ["CMD", "wget", "--spider", "-q", "http://localhost/health"]

# ✗ AVOID - pagina pesante
test: ["CMD", "wget", "--spider", "-q", "http://localhost/big-data"]
```

### 2. Timeout Appropriati
```yaml
# ✓ GOOD - timeout proporzionato all'interval
interval: 10s
timeout: 3s

# ✗ AVOID - timeout troppo lungo
interval: 10s
timeout: 30s  # Riduce frequenza dei check
```

### 3. Retries Adeguati
```yaml
# ✓ GOOD - più retries per servizi lenti (database)
healthcheck:
  retries: 5

# ✓ GOOD - meno retries per servizi veloci (web)
healthcheck:
  retries: 3
```

## Debugging

### Testare manualmente
```bash
docker exec lab03-web wget --spider -q http://localhost/health
echo $?  # 0 = success, !0 = failure
```

### Vedere log healthcheck
```bash
docker inspect lab03-web --format '{{range .State.Health.Log}}{{.Output}} {{end}}'
```

### Reset health status
```bash
docker restart lab03-web
```

## Vedi Anche
- Tutorial: Implementare Healthchecks
- Reference: Healthcheck Syntax