How to add a response header on nginx when using proxy pass

When proxying requests to backend servers in Nginx, it's sometimes necessary to add custom headers to the response. This can be achieved using the add_header directive, which is commonly specified within server or location blocks.

Here is an example of adding custom response headers in an Nginx configuration file:

nginx
server {
    listen 80;
    server_name example.com;

    location / {
        proxy_pass http://backend_server; # This is your backend server address
        add_header X-Proxy-Cache $upstream_cache_status;

        # Other proxy settings, such as setting proxy headers
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

In the above configuration, we add a custom response header named X-Proxy-Cache for all requests proxied through the / location block. The value is set to the $upstream_cache_status variable, which typically indicates the caching status of the backend server.

Note that the add_header directive can add both constant values and dynamically generated values using Nginx variables. However, if you use add_header, you must ensure all default headers are included, as it overrides Nginx's default behavior and only outputs headers explicitly defined in your configuration.

The above configuration is a simple example; you can add other response headers or configure more complex settings as needed.

You can try this solution:

Within your location block, when using proxy_pass, do the following:

shell
location ... {

  add_header yourHeaderName yourValue;
  proxy_pass xxxx://xxx_my_proxy_addr_xxx;

  # Now use this solution:
  proxy_ignore_headers yourHeaderName // but set by proxy

  # Or if above didn't work, try this:
  proxy_hide_header yourHeaderName // but set by proxy

}

I'm not sure if this is exactly what you need, but modifying this approach might work for your issue.

You can also use this combination:

shell
proxy_hide_header headerSetByProxy;
set $sent_http_header_set_by_proxy yourValue;

The add_header directive works effectively regardless of whether proxy_pass is present or not. I just set up a configuration where I used this directive today. But I must admit that I encountered difficulties during the setup process, though I don't recall the exact reason.

Now I have a working configuration that includes the following (among other things):

nginx
server {
    server_name  .myserver.com
    location / {
        proxy_pass  http://mybackend;
        add_header  X-Upstream  $upstream_addr;
    }
}

Compared to the HttpHeadersMoreModule mentioned in Sebastian Goodman's Stack Overflow answer (link), the add_header directive in nginx versions prior to 1.7.5 only applied to successful responses.

Since nginx 1.7.5, you can include custom headers in error responses using the always keyword. For example:

nginx
add_header X-Upstream $upstream_addr always;

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Limitation: You cannot use add_header to override header values in the server context.