adrelanos's questions

The backend server sets the Cache-Control HTTP header but the frontend might manipulate it. For debugging it would be useful to see the Cache-Control HTTP header as the backend had set it. Hence wondering, it it possible on the backend server to set custom (X-) header that contains the same value as Cache-Control?

I tried the following already:

more_set_headers "X-Backend-Cache-Control: $http_cache_control";

But that didn't work. No header has been added.

It's not an issue with more_set_headers. The following worked:

more_set_headers "X-Backend-Cache-Control: test";

A header was added. But that was just a simple test to see headers can be set at all and not useful obviously.

If nginx is already used with proxy_cache, is there still any need to use fastcgi_cache?

In other words.. When using nginx proxy_cache, there is no more need for fastcgi_cache?

I would like to modify the html as it comes from the webapp before delivering it to the website visitor. However, if the website visitors posts in a web formula the input is also transformed by nginx's subs_filter.

Is it possible to use nginx's subs_filter for GET request only but not for POST?

Similar question (non-duplicate!) nginx sub_filter for GET request only?

nginx FAQ Is there a proper way to use nginx variables to make sections of the configuration shorter, using them as macros for making parts of configuration work as templates? ) saying (bold is mine):

Q: Is there a proper way to use nginx variables to make sections of the configuration shorter, using them as macros for making parts of configuration work as templates?

A: Variables should not be used as template macros. Variables are evaluated in the run-time during the processing of each request, so they are rather costly compared to plain static configuration. Using variables to store static strings is also a bad idea. Instead, a macro expansion and "include" directives should be used to generate configs more easily and it can be done with the external tools, e.g. sed + make or any other common template mechanism.

For example instead of one super long add_header Content-Security-Policy for better readability I am using:

set $CSP "default-src 'none'";

set $CSP "${CSP}; connect-src 'self'";

set $CSP "${CSP}; script-src 'self' https://*.domain.org 'unsafe-inline' 'unsafe-eval'";

set $CSP "${CSP}; style-src 'self' https://*.domain.org 'unsafe-inline'";

set $CSP "${CSP}; img-src 'self' data: https://*.domain.org";

set $CSP "${CSP}; font-src 'self' https://*.domain.org";

## CSP closing colon.
set $CSP "${CSP};";

add_header Content-Security-Policy "$CSP";

How much impact on nginx performance would that use of variable have appropriately? Has there been any performance testing / research on that subject?