How do I add no-cache headers to all 404 pages served by apache and nginx?

I have recently run into an issue after switching to Cloudflare, and the solution is to basically stop Cloudflare from caching 404 responses.

In our load-balanced multi-server setup, occasional 404s happen, but they're quickly fixed by rsync (via lsyncd). Before Cloudflare, a re-request to the 404ed file would very quickly become 200 as rsync does its job.

However, since Cloudflare caches all data based on the caching header, and neither apache nor nginx send a no-cache header for 404s, Cloudflare ends up caching the 404 response for a while.

I've been searching for a solution to globally add such a header for 404s in both apache and nginx (globally, for all hosted domains), but so far have come up blank.

Can anyone help?

Thank you.

Can't you get by with using an error_page directive, and then handle the location separately with the added header?

e.g. in Nginx:

    server {
      ...
      error_page 404 /404.html;
      location = /404.html {
        root   /usr/share/nginx/html;
        add_header Cache-Control "no-cache" always;
      }
    }

In apache 2.4, you could try something like:

FileETag None
<IfModule mod_headers.c>
    Header always unset ETag "expr=%{REQUEST_STATUS} == 404"
    Header always set Cache-Control "max-age=0, no-cache, no-store, must-revalidate" "expr=%{REQUEST_STATUS} == 404"
    Header always set Pragma "no-cache" "expr=%{REQUEST_STATUS} == 404"
    Header always set Expires "Wed, 11 Jan 1984 05:00:00 GMT" "expr=%{REQUEST_STATUS} == 404"
</IfModule>

The always is important because this is a:

You're adding a header to a locally generated non-success (non-2xx) response, such as a redirect, in which case only the table corresponding to always is used in the ultimate response.

You said all 404s, but for full reference of course it might make sense to wrap that in a <FilesMatch> or <LocationMatch> to limit the scope.

I believe this is a new capability in apache 2.4 as using expr conditionals is not the in the 2.2 version of the mod_headers documentation.

curl -I [foo] test without this config:

HTTP/1.1 404 Not Found
Date: Thu, 24 May 2018 17:44:29 GMT
Server: Apache/2.4.18 (Ubuntu)
Content-Type: text/html; charset=iso-8859-1

curl -I [foo] test with this config:

HTTP/1.1 404 Not Found
Date: Thu, 24 May 2018 17:44:42 GMT
Server: Apache/2.4.18 (Ubuntu)
Cache-Control: max-age=0, no-cache, no-store, must-revalidate
Pragma: no-cache
Expires: Wed, 11 Jan 1984 05:00:00 GMT
Content-Type: text/html; charset=iso-8859-1

Sources:

http://httpd.apache.org/docs/current/mod/mod_headers.html

You can do it this way too :

map $status $cache_header {
    default <for_other_codes>;
    404     "no-cache";
}


server {

    [ ... ]

    add_header "Cache-Control" $cache_header always;

}