====== revproxy ======

===== variables =====

==== $host vs $http_host vs $server_name ====

From: [[https://serverfault.com/questions/706438/what-is-the-difference-between-nginx-variables-host-http-host-and-server-na|What is the difference between Nginx variables $host, $http_host, and $server_name?]]

**You should almost always use** ''$host'', as it's the only one guaranteed to have something sensible regardless of how the user-agent behaves, unless you specifically need the semantics of one of the other variables.

The difference is explained in the nginx documentation:
  * ''$host contains'' "in this order of precedence: host name from the request line, or host name from the 'Host' request header field, or the server name matching a request"
  * ''$http_host'' contains the content of the HTTP "Host" header field, if it was present in the request
  * ''$server_name'' contains the server_name of the virtual host which processed the request, as it was defined in the nginx configuration. If a server contains multiple server_names, only the first one will be present in this variable.


===== app behind path =====

Search tags:
  * proxy_pass subfolder
  * path based routing

When hosted app requests assets from absolute URI like: ''/app.png'', all requests are directed to root ''/'' location.

Analysis of sent headers shows that there is only one header preserving original subfolder: ''Referer:''.  

[[https://serverfault.com/questions/1101045/nginx-serve-application-under-sub-path|NginX: Serve application under sub path]]


<code>
    location /mqttx {
        return 302 /mqttx/;
    }

    location /mqttx/ {
        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;

        proxy_pass             http://mqttx-web/;
    }

    # mqttx-web loads assets:
    # - /app.js
    # - /app.png
    # - /favicon.ico
    # from absolute paths!
    # so it is impossible to host it under /mqttx/ without this trick:
    if ($http_referer ~ ^https://mqtt.grinndev.ovh/mqttx/) {
       rewrite ^ /mqttx$uri;
    }
</code>