Retrospective web development exercise for the 2018 archive.

When a request fails, note the URL, the time, and what the browser showed. Find the matching line in the web server’s access log, then look for an application error near the same time. Keeping the request in view makes it easier to ignore unrelated warnings.

Try this with a deliberate missing route on a local site. Compare the entry for that request with the entry for a working one. If the app and the proxy log different statuses, trace where the change happened. A browser error page is a starting point; the logs can tell you which component handled the request.