Networking
502 Bad Gateway From Nginx: Which Side Is Actually Broken
The proxy is telling you your application failed. Here is how to read the error log line and identify which of six things went wrong.
Docker
Permission Denied in a Container When the File Is Right There
Non root containers break in predictable ways. Here is how UID mapping, volume ownership, and read only filesystems produce the same error.
Docker
Docker Build Works Locally and Fails in CI: The Eight Causes
Same Dockerfile, same repo, different result. The difference is nearly always cache, context, architecture, or something on your machine that is not in the…
Shopify
Liquid Error: Nothing Renders and There Is No Error Message
Liquid fails quietly by design. Here is where the error actually goes and how to make your theme tell you what went wrong.
Node.js
EADDRINUSE: Finding and Killing Whatever Took Your Port
Address already in use. Here is how to find the process, why it sometimes is not a process at all, and why the port stays busy after you kill it.
JavaScript
Maximum Call Stack Size Exceeded When It Is Not Recursion
Sometimes it is infinite recursion. Often it is spreading a large array into a function call, and the fix is completely different.
Networking
x509: certificate signed by unknown authority
Your browser trusts the certificate and your application does not. They use different trust stores, and inside a container there may not be one at all.
React
Too Many Re-renders: Finding the Infinite Loop in React
React caught the loop and stopped it. Here are the five ways to create one and how the Profiler tells you which you have.
JavaScript
Unexpected token < in JSON at position 0 Means You Got HTML
The angle bracket is the first character of an HTML error page. Your API returned a page, not JSON, and here is how to find out which page.
Networking
Your Cache-Control Header Is Probably Wrong
no-cache does not mean do not cache. max-age on a CDN is not what you think. Here is what each directive actually does.
JavaScript
No Access-Control-Allow-Origin: What CORS Is Really Doing
CORS errors are a browser protecting you from a response it already received. Understanding that one fact makes every CORS error obvious.
Tooling
fatal: refusing to merge unrelated histories
Git is protecting you from combining two repositories that share no common ancestor. Sometimes that is exactly what you want.