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Pascual Vila

Frontend Instructor // Code Syllabus

Common Pitfalls & Errors

The Error //

Implementing a health check that unconditionally returns 200 OK regardless of actual application state

// Wrong: no actual signal
app.get("/health", (req, res) => res.sendStatus(200));

// Correct: verifies what actually matters
app.get("/health/ready", async (req, res) => {
  res.sendStatus(await db.ping() ? 200 : 503);
});

The Solution //

This provides zero real signal to the orchestrator or load balancer — an instance that has completely lost its database connection still reports itself as perfectly healthy, so traffic keeps being routed to (or the instance is never restarted despite) a genuinely broken service. A meaningful health check must actually verify the critical dependencies it relies on.

The Error //

Querying a dependency inside a health check with no timeout of its own

// Wrong: no bound on how long this can hang
await db.query("SELECT 1");

// Correct: strict, short timeout independent of the check
await db.query("SELECT 1", { timeout: 2000 });

The Solution //

If the dependency being checked (like a database) is slow rather than fully down, an unbounded check can hang the health endpoint itself indefinitely — turning the health check into an additional point of failure, and potentially causing the orchestrator's own probe to time out in a way that behaves unpredictably.