class HealthChecker {
  async checkDatabase() {
    const start = Date.now();
    try {
      await db.query('SELECT 1');
      return { status: 'healthy', latency: Date.now() - start };
    } catch (err) {
      return { status: 'unhealthy', error: String(err?.message || err) };
    }
  }

  async checkRedis() {
    try {
      await redis.ping();
      return { status: 'healthy' };
    } catch (err) {
      return { status: 'unhealthy', error: err.message };
    }
  }

  async getReadiness() {
    const checks = await Promise.all([
      this.checkDatabase(),
      this.checkRedis()
    ]);
    const healthy = checks.every(c => c.status === 'healthy');
    return { healthy, checks };
  }
}

// Liveness - lightweight
app.get('/health/live', (req, res) => {
  res.json({ status: 'ok', timestamp: new Date().toISOString() });
});

// Readiness - check dependencies
app.get('/health/ready', async (req, res) => {
  const health = await healthChecker.getReadiness();
  res.status(health.healthy ? 200 : 503).json(health);
});

Kubernetes Configuration

livenessProbe:
  httpGet:
    path: /health/live
    port: 3000
  initialDelaySeconds: 15
  periodSeconds: 10
  failureThreshold: 3

readinessProbe:
  httpGet:
    path: /health/ready
    port: 3000
  initialDelaySeconds: 5
  periodSeconds: 10

Best Practices

Keep liveness checks minimal (no external deps)
Check only critical systems in readiness
Return 200 for healthy, 503 for unhealthy
Set reasonable timeouts to prevent cascading failures
Include response time metrics

Additional Implementations

See references/implementations.md for:

Python Flask complete health checker
Java Spring Boot Actuator
Full Kubernetes deployment config

Never Do

Make liveness depend on external services
Return 200 when dependencies are down
Skip dependency checks in readiness

Probe	Purpose	Failure Action
Liveness	Is process alive?	Restart container
Readiness	Can handle traffic?	Remove from LB
Startup	Has app started?	Delay other probes
Deep	All deps healthy?	Trigger alerts

health-check-endpoints

Health Check Endpoints

Probe Types

Implementation (Express)