Your Node.js API is responding with 502 errors under load. Here's the relevant code and infrastructure: - Express.js API behind an Nginx reverse proxy - Connection pool to PostgreSQL (max 20 connections) - Average response time: 50ms normally, 30s+ during incidents - Error logs show: "connect ETIMEDOUT" and "too many clients already" - The issue starts when traffic exceeds 200 req/s ```javascript app.get('/api/users/:id', async (req, res) => { const client = await pool.connect(); const result = await client.query('SELECT * FROM users WHERE id = $1', [req.params.id]); res.json(result.rows[0]); }); ``` What's wrong? Provide the fix and explain the connection pool exhaustion pattern.