### Reverse proxy


#### Introduction
A reverse proxy is for example used to host 2 services on the same port. This is useful for us because we can use the same port for the websockets and the webserver. 

#### How to use a reverse proxy
We are going to use `Apache2` as our reverse proxy. This is because it is easy to use and has a lot of documentation. It also hosts our webserver so it is easy to configure and we don't have to install another program.

#### Additional modules
We need to enable the `proxy` and `proxy_wstunnel` modules. These are used to proxy the websockets.

You can install them with these commands on a Raspberry Pi. For other linux distributions its may be different.

```bash
$ sudo a2enmod proxy
$ sudo a2enmod proxy_wstunnel
```

#### Script
The enabled apache2 config scripts are found in `/etc/apache2/conf-enabled/`. You can create a new file with the name of your service. For example `studyarea.conf`.
```apache
<VirtualHost *:80>
    DocumentRoot /home/pi/www/html/

    # Enable proxying WebSockets
    ProxyPass /ws ws://localhost:8001/

    # Enable proxying HTTP
    ProxyPass /ws http://localhost:8080/
</VirtualHost>
```
Because VirtualHost is listening on port 80, we can use the same port for the webserver and the websockets. The `ProxyPass` is used to proxy the websocket. The `/ws` is the path where the websockets are hosted. Its hosted on `localhost/ws` so it kinda creates a new subdomain for the websocket. The `localhost:8001` is the address of the websockets and the `localhost:8080` is the address of the webserver.


`DocumentRoot` is the path where the files are for the website.



### Sources:

* https://httpd.apache.org/docs/2.4/howto/reverse_proxy.html
* https://www.serverlab.ca/tutorials/linux/web-servers-linux/how-to-reverse-proxy-websockets-with-apache-2-4/
* https://gist.github.com/mortenege/91ec6fe02dca6f736303a00f8cea2731
* https://www.jscape.com/blog/forward-proxy-vs-reverse-proxy#:~:text=While%20a%20forward%20proxy%20proxies,is%20providing%20file%20transfer%20services.
* https://webmasters.stackexchange.com/questions/143106/functional-difference-between-proxypass-and-proxypassreverse-in-apache