Node.js has a reputation for being “fast by default,” which is both true and dangerously misleading. Many Node.js APIs don’t fail because Node itself is slow, they fail because the system around it was designed without understanding how the event loop behaves under pressure.
**The most common mistake is assuming async automatically means scalable. **Async code can still block the event loop through CPU-heavy work, excessive JSON parsing, synchronous crypto, or poorly bounded concurrency. When the event loop is blocked, latency spikes across every request, not just the slow endpoint.
Another frequent issue is unbounded parallelism. Firing off database queries or downstream HTTP calls without limits feels efficient until traffic grows. At that point, you’re no longer serving users, you’re exhausting your own resources.
The fix is rarely exotic. Profile real traffic. Limit concurrency intentionally. Push CPU-heavy work out of the request path. Use timeouts everywhere. Treat the event loop as a shared, finite resource, because it is.
If you design with those constraints in mind, Node.js scales extremely well. If you ignore them, it tends to fail loudly and all at once.
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