nginx: How to backup / duplicate nginx Cache-Control header?

adrelanos

12/15/23, 5:32 PM

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.

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Danila Vershinin

12/17/23, 7:08 AM

You're looking for the $sent_http_cache_control variable. This will contain the response's Cache-Control value, so:

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

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adrelanos

12/17/23, 5:02 PM

Did you test this? Unfortunately this also does not work for me.

Danila Vershinin

12/17/23, 6:39 PM

@adrelanos Yes. It should be applied on your front-end server, e.g. alongside `proxy_pass`.

adrelanos

12/20/23, 7:12 PM

I was setting it in the backend. That didn't work. Setting it in the frontend worked. I was hoping it's possible to set this setting in the backend.

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Server

Tero Kilkanen

12/15/23, 10:47 PM

The $http_ variables contain HTTP headers from the HTTP request, as shown in nginx documentation.

I don't know if there is a way to refer to HTTP response headers in nginx.

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