Nginx / Apache Config Explainer

How this reads your output

Each line is matched against the directives that turn up most often in real configurations, and explained with the behaviour that actually catches people rather than a restatement of the manual. Alongside that, the whole block is checked for omissions: a proxy without a Host header, a reverse proxy without the forwarded protocol header, TLS with no explicit protocol list. Those are not syntax errors, so the configuration loads and works until the specific situation each one causes.

What the results mean

Worth a second look

Directives whose behaviour differs from what most people assume, such as the trailing slash on proxy_pass or how add_header inheritance works.

Common omissions

Missing directives that cause real problems later. A reverse proxy without forwarded headers is the usual source of redirect loops.

Detected server

Whether the block reads as nginx or Apache, chosen by which directive vocabulary appears more often.

Common problems and fixes

A backend behind the proxy redirects in a loop

The backend cannot tell it is behind TLS termination, so it sees plain HTTP and issues a redirect to HTTPS, which arrives back as plain HTTP again. Set X-Forwarded-Proto and Host on the proxy, and configure the application to trust them. This is the single most common reverse proxy fault and it is entirely about headers.

Security headers disappeared from some responses

In nginx, add_header does not inherit: a single add_header inside a location block discards every add_header from the enclosing server block. Either repeat them in each block that adds one, or use the always variant with a module that merges them. The behaviour is documented and still surprises everyone.

Frequently asked questions

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