nginx -t returns syntax is ok and test is successful. nginx -s reload finishes without a complaint. Nothing shows up in the error log.
And yet the behavior is wrong.
I've done this to myself more times than I'd like to admit. The one that hurt most was a CSP header I shipped to production that never reached a single browser for a full day — I only noticed because I got suspicious that no violation reports were coming in. There have been others: a file I put under /static/ getting swallowed by a different location, old behavior lingering after a reload. In every case nginx -t passed, and nothing was grammatically wrong anywhere.
The nature of this gap is clear: nginx -t validates only syntactic correctness, and never looks at semantic correctness.
What nginx -t actually guarantees for you
