Sign in with Google worked locally and on staging but failed in production with redirect_uri_mismatch. Behind the TLS proxy our FastAPI app built an http:// callback because Uvicorn did not trust the proxy's headers. How we traced and fixed it.
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 chat assistant streamed tokens smoothly on localhost but in production the whole answer appeared after 14 seconds. nginx was buffering the event stream and gzip was holding bytes. How we proved it with curl and fixed it without breaking other routes.
Uploading a PDF larger than 1 MB failed with a vague error in our claims portal. Nginx returned 413, then PHP silently dropped files, then Laravel rejected them. Four layers each had their own size limit. Here is how we aligned them and tested every boundary.
Our PayPal checkout button rendered in development and staging but was an empty box in production. A new Content-Security-Policy set in Nginx blocked the PayPal SDK script, its iframes and its API calls. We fixed it per directive, with a nonce and a report-only rollout.
Moving our SPA from cookie auth to bearer tokens broke every API call with a CORS error. The Authorization header triggered an OPTIONS preflight, our nginx auth check rejected it, and error responses carried no CORS headers.
Minutes after we proxied our marketing site through Cloudflare, every visitor hit ERR_TOO_MANY_REDIRECTS. Cloudflare's Flexible mode spoke plain HTTP to an origin that redirected all HTTP to HTTPS. Full (strict) with an origin certificate ended the loop.
Our customer portal went dark at 07:12 when its Let's Encrypt certificate expired. Certbot's timer had run twice a day for a month and failed every time, because a firewall change blocked port 80. Here is how we traced it, fixed it and made expiry impossible to miss.
Our API certificate renewal looked perfect in desktop Chrome, yet the Android app, curl and a partner's Java service all rejected it. The server sent only the leaf certificate without the intermediate. Serving the full chain fixed every client at once.
After moving our PHP app to a new Ubuntu 24.04 server, every page returned 502 Bad Gateway. Fixing socket ownership got us online, then traffic spikes brought the 502s back from an undersized FPM pool. Here is how we fixed both.