Our queue workers took exactly 30 seconds to stop on every deploy and lost the job they were processing. Exit code 137 in every pod. The Dockerfile used shell-form CMD, so /bin/sh was PID 1 and never forwarded SIGTERM to Node. Exec form plus a real shutdown handler fixed it.
We once spent two weeks optimizing SQL for an endpoint whose real cost was a logging call. Since then every performance task starts with a profile. Here is how we capture flame graphs in PHP, Node.js and Python, how to read them, and how to measure the win.
After we set "type": "module" in package.json, jest.mock stopped replacing our mailer and tests started calling the real SMTP client. Static ESM imports are linked before any mock runs. Here is the mechanism and the fix with unstable_mockModule.
Our partner OAuth server matched redirect_uri by prefix, and our login page followed any next URL. Chained together with a legacy implicit flow, an access token could land on an outside domain. We moved to exact matching, relative-only next and code plus PKCE.
After we turned on streaming for our assistant, tool calls failed with JSON parse errors and sometimes ran with another call's arguments. We were parsing argument fragments per chunk and keying them by arrival order. Accumulating by index fixed it.
Our nightly report export ran perfectly when we typed it, and failed every night as a systemd service with node: command not found. Services get no login shell, no .bashrc and a working directory of /. Here is how we made the unit self-contained.
A low but stubborn rate of 502s at the load balancer and socket hang up errors between services turned out to be one race: Node closed idle keep-alive connections after 5 seconds while its callers kept reusing them.
Every deploy and every traffic burst, the first requests to our booking API timed out and Postgres started refusing clients. The handler did heavy setup and opened a fresh connection per invocation. Moving init out of the handler and adding RDS Proxy fixed it.
Users were logged out at random, mostly in the afternoon. Sessions and a fast-growing cache shared one Redis with allkeys-lru, so every hourly cache warm-up evicted idle sessions. Separate DB numbers would not have helped; separate instances did.
Our live support chat dropped every connection that stayed quiet for a minute, with close code 1006 and no server error. Nginx's 60-second proxy_read_timeout and the load balancer idle timeout were closing idle sockets. A heartbeat plus proxy tuning fixed it.
Our PDF invoices and the amounts charged through Stripe disagreed by a cent on 214 invoices in one month. Floats, toFixed and rounding at every step were to blame. We moved to integer minor units with one explicit rounding point.
Bumping React to 19 made npm install fail with ERESOLVE. The quick --legacy-peer-deps workaround installed, then crashed tooltips in staging. We learned to read the conflict, upgrade the real offender and use overrides only as a short, tested bridge.
Our storefront BFF pods restarted every few hours with OOMKilled and exit code 137, then fell into CrashLoopBackOff during the holiday peak. A max-old-space-size inherited from the VM days was double the container memory limit. Sizing the heap to the limit and bounding a cache fixed it.
Our price streaming API grew from 180 MB to 1.4 GB of heap in a day and was restarted by the orchestrator every night. A listener was attached to a shared EventEmitter on every request and never removed. Heap snapshots proved it; removing listeners on close fixed it.
After a harmless-looking Express refactor, every Stripe webhook failed verification and paid bookings stayed pending. A global JSON parser consumed the body before constructEvent saw it. How we found it, fixed the route and replayed the missed events.
An internal reporting service read the user ID and role from a JWT with jwt.decode(), which never checks the signature. A route that bypassed our gateway let any edited token through. We switched to verification with a pinned algorithm, issuer, audience and JWKS rotation.
Our API container crashed with ECONNREFUSED on about one in five CI runs and on every fresh laptop setup. depends_on only waited for the Postgres container to start, not to accept connections. A real healthcheck, service_healthy and a small retry loop fixed it.