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====== Web Servers - Nginx - Setup Nginx Reverse Proxy ======

A Reverse Proxy sits between a client and a web server (or servers) and acts as a **frontend** by handling all incoming client requests and distributing them to the backend web, database, and/or other server(s).

Other benefits of a Reverse Proxy include:

  * **Load balancing**:  The reverse proxy distributes incoming connections to backend servers, and can even do so according to the current load that each server is under.
    * This ensures that none of the backend servers get overloaded with requests.
    * It also prevents downtime, since the reverse proxy can reroute traffic if a backend server happens to go offline.
  * **Central logging**:  Rather than having multiple servers generate log files, the reverse proxy can log all relevant information in a single location.
    * This makes the administrator’s job immensely easier, since problems can be isolated much more quickly and there is no need to parse log files from multiple locations when troubleshooting issues.
  * **Improved security**:  A reverse proxy will obfuscate information about the backend servers, as well as act as a first line of defense against incoming attacks.
    * Since the reverse proxy is filtering out traffic prior to forwarding it to the backend, only innocuous traffic is passed along to the other servers.
  * **Better performance**: A reverse proxy server can make smart decisions about how to distribute the load across backend servers, which results in speedier response times.
    * Other common server tasks such as caching and compression can also be offloaded to the reverse proxy server, freeing up resources for the backend servers.


----

===== Install NginX =====


<code bash>
sudo apt install nginx
</code>

----

===== Disable the default virtual host =====

<code bash>
unlink /etc/nginx/sites-enabled/default
</code>

----

===== Create a reverse proxy configuration file =====

All of the settings for the reverse proxy will go inside of a configuration file, and this file needs be placed inside the **sites-available** directory.

<code bash>
cd /etc/nginx/sites-available
</code>

Create the configuration file:  /etc/nginx/sites-available/reverse-proxy.conf

<file bash /etc/nginx/sites-available/reverse-proxy.conf>
server {
    listen 80;
    location /some/path/ {
        proxy_pass http://example.com;
    }
}
</file>

<WRAP info>
**NOTE:**  This will work for HTTP servers, but Nginx also supports other protocols.

  * Replace example.com with the IP address or hostname of the server you are forwarding to.
    * A port can also be specified with the hostname, such as 127.0.0.1:8080.

</WRAP>

----

===== Enable the proxy =====

Enable the new configuring by creating a symbolic link to the **sites-enabled** directory:

<code bash>
ln -s /etc/nginx/sites-available/reverse-proxy.conf /etc/nginx/sites-enabled/reverse-proxy.conf
</code>

----

===== Proxy Non-HTTP servers =====

Nginx can also act as a reverse proxy for FastCGI, uwsgi, SCGI, and memcached.

Rather than using the **proxy_pass** directive shown above, replace it with the appropriate type:

  * **proxy_pass**: (HTTP server – as seen above)
  * **fastcgi_pass**:  FastCGI server.
  * **uwsgi_pass**:   uwsgi server.
  * **scgi_pass**:   SCGI server.
  * **memcached_pass**:  Mmemcached server.

----

===== Pass Headers =====

To configure what headers the reverse proxy server passes to the other server(s), define them in the same /etc/nginx/sites-available/reverse-proxy.conf configuration file.

Use the **proxy_set_header** directive to adjust the headers.

  * They can be configured in the server, location, or http block.

<file bash /etc/nginx/sites-available/reverse-proxy.conf>
location /some/path/ {
        proxy_set_header HOST $host;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_pass http://example.com;
}
</file>

<WRAP info>
**NOTE:**  This defines three types of headers and sets them to the respective variables.

  * There are a lot of different options for passing headers.

  * **Host**:  contains information about which host is being requested.
  * **X-Forwarded-Proto**:  species if the request is HTTP or HTTPS.
  * **X-Real-IP**:  contains the IP address of the requesting client.

</WRAP>