Health Check Endpoints

Implement health checks for monitoring service availability and readiness.

Probe Types

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

Implementation (Express)

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);
});