Nginx proxy - proxy_set_header - custom header from site.conf (For Varnish Cache)

Is it possible to send a custom header in your website and then forward it using proxy_set_header to Varnish?

Info

I have moved folder locations a little bit - everything are included correctly and works.

I have /etc/nginx/conf.d/params/proxy.params/proxy_params file with:

proxy_set_header Host $http_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-Port-Nginx $server_port;
proxy_set_header X-Forwarded-DocumentRoot $document_root;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header Ssl-Offloaded $scheme;
proxy_set_header X-Forwarded-Custom-Location-Site 'Custom Site';   ### THIS IS THE HEADER I WANT TO BE DYNAMIC
fastcgi_param  HTTPS on;

Then in my https server block in sites-enabled/custom-site.conf:

server {
    listen 443 ssl default_server;
    server_tokens off;
    add_header 'Access-Control-Allow-Origin' '*';
    add_header 'Custom-Location-Site' 'mysite1';
    root /var/www/html;
    server_name nginx-glo 192.168.1.105 localhost:443;

    location / {
        access_log /var/log/nginx/access.log main;
        add_header 'Custom-Nginx-Server-Location-Root-Redirect' 'From /';   #### This header does not appear in varnishlog  (testing only)
        include /etc/nginx/conf.d/params/proxy.params/proxy_params_destination.conf;

The relevant proxy_params_destination.conf:

server_tokens off;

proxy_redirect off;
include /etc/nginx/conf.d/params/proxy.params/proxy_params;
# Try not to add headers using add_header, this will reset all headers from other locations
# that are redirected here.
# Also do not log to file here, log in locations above.

proxy_headers_hash_bucket_size 356;
proxy_read_timeout 3600;
proxy_connect_timeout 60;
# Cannot use https:// for proxy calls - use http, outside connection is https
proxy_pass http://varnish-cache-magento2.3.5:6081;
#proxy_pass http://web-server-apache2-magento2.3.5:8080;

What I want to do:

I have this header defined : add_header 'Custom-Location-Site' 'mysite1' in the website conf file.
I want to receive the _value from that header for each website_and forward it here:
proxy_set_header X-Forwarded-Custom-Location-Site $how_can_I_get_Custom-Location-Site_here; and then let Varnish cache receive this header in vcl_recv{}
This forwarded header I will then handle in vcl_recv{}:
using req.http.X-Forwarded-Custom-Location-Site as descibed in sample below.

Reason:

Varnish cache setup for multiple Magento 2 sites.

The sample from Varnish article below shows how I can do it with paths. I can not use Paths, I have multiple Docker containers running different websites, and then forwards it to the Varnish container. For example Container that runs PHP 7.2, other PHP 7.3 websites, both running inside as /var/www/html, https

Link to sample multiple backends

Relevant section in sample:

sub vcl_recv {
    if (req.url ~ "^/java/") {
        set req.backend_hint = java;
    } else {
        set req.backend_hint = default;
    }
}

backend default {
    .host = "127.0.0.1";
    .port = "8080";
}
Now let’s add a new backend:

backend java {
    .host = "127.0.0.1";
    .port = "8000";
}

Varnishlog

As shown here: varnishlog already receives my custom headers in the Docker container. I just now need the value of the custom header to be dynamic.

-   ReqHeader      X-Real-IP: 192.168.1.103
-   ReqHeader      X-Forwarded-For: 192.168.1.103
-   ReqHeader      X-Forwarded-Port-Nginx: 443
-   ReqHeader      X-Forwarded-DocumentRoot: /var/www/html
-   ReqHeader      X-Forwarded-Proto: https
-   ReqHeader      Ssl-Offloaded: https
-   ReqHeader      X-Forwarded-Custom-Location-Site: Custom Site

Solution

If I understood correctly, this is what you need:

proxy_set_header X-Forwarded-Custom-Location-Site $http_custom_location_site;

This makes the X-Forwarded-Custom-Location-site dynamic, based on the server block where you configured the Custom-Location-Site header.

If for example the value of Custom-Location-Site is mysite1, the X-Forwarded-Custom-Location-site value will be the following:

X-Forwarded-Custom-Location-site: mysite1

According to http://nginx.org/en/docs/http/ngx_http_core_module.html#var_http_, you can use $http_ with any header. You just have to lowercase the value, and replace dashes with underscores.