nginx proxy_cache_key with a single $scheme

Question

I have tested proxy_cache_key with a single $scheme

 proxy_cache_key $scheme;
 proxy_pass http://127.0.0.1:8081/;

Then I request one to cache.

curl http://127.0.0.1:8080/a.html

Then I requested again to confirm the cache

curl http://127.0.0.1:8080/a.html

No problem

Then I request other url

curl http://127.0.0.1:8080/b.html

And hope that it hits cache because the key is $scheme

but it gave me the content of b.html

Why proxy_cache_key $scheme; does not work?

Answer 1

The headers from the proxied server response can change the "final" cache key.

From https://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_ignore_headers :

If not disabled, processing of these header fields has the following effect:

• “X-Accel-Expires”, “Expires”, “Cache-Control”, “Set-Cookie”, and “Vary” set the parameters of response caching;

You can check if those headers are included in the response and/or try ignoring them.