Database Health Check Component Design

Database Health Check

The database health check is the most critical component in any health check endpoint. A failed database usually means the service cannot function.

Response Component

{
  "database": {
    "status": "UP",
    "duration": "12ms",
    "message": "PostgreSQL connection pool active",
    "details": {
      "type": "postgresql",
      "poolSize": 20,
      "activeConnections": 5,
      "idleConnections": 15,
      "waitingRequests": 0
    }
  }
}

What to Check

1. Connection availability: Can you get a connection from the pool?
2. Query execution: Run a simple SELECT 1 query
3. Latency: Is the response time within acceptable limits?
4. Pool health: Are connections being created and recycled properly?
5. Replication lag: For read replicas, is data reasonably current?

Implementation Pattern

async function checkDatabase() {
  const start = Date.now();
  try {
    await pool.query('SELECT 1');
    const duration = Date.now() - start;
    return {
      status: duration < 100 ? 'UP' : 'DEGRADED',
      duration: `${duration}ms`,
      message: `Query completed in ${duration}ms`
    };
  } catch (error) {
    return {
      status: 'DOWN',
      duration: `${Date.now() - start}ms`,
      message: error.message
    };
  }
}

Threshold Guidelines

Metric	Healthy	Degraded	Unhealthy
Query latency	< 50ms	50-500ms	> 500ms
Pool utilization	< 70%	70-90%	> 90%
Replication lag	< 1s	1-10s	> 10s