How to Configure Apache as a Reverse Proxy with mod_proxy?

Apache is a powerful web server application that can serve dynamic web content or act as a reverse proxy. As a reverse proxy, it forwards client requests to backend servers. This guide will demonstrate how to configure Apache as a reverse proxy using the mod_proxy module.

This guide will walk you through proxying an ownCloud application running on port 8080 within a Docker container. The same process can be applied to other applications running on different ports.

Requirements

• Deploy a new Vultr Cloud Server.

Note: This article uses an Ubuntu 20.04 server, but the instructions are also applicable to other Linux servers running Apache.

• Set up a DNS “A” record pointing to the server’s IP address. This guide uses the name app.example.com.
• Connect to the server.
• Log in as a non-root user with sudo privileges.
• Update the server.
• Install Apache.
• Install Docker.

1. Enable mod_proxy

• Enable mod_proxy in Apache.
• To start configuring Apache as a reverse proxy, enable the necessary modules.
• Enable the core mod_proxy module:

sudo a2enmod proxy

Enable additional proxy-related modules:

sudo a2enmod proxy_http
sudo a2enmod proxy_balancer
sudo a2enmod proxy_wstunnel

These modules are responsible for:

• mod_proxy: Provides the fundamental proxying capabilities.
• proxy_http: Handles HTTP and HTTPS proxy requests.
• proxy_balancer: Enables load-balancing functionality.
• proxy_wstunnel: Allows WebSocket tunneling to a backend server.

• Restart Apache to apply these changes:

sudo systemctl restart apache2

2. Set up the Back-end Application

• As an example, we will set up an ownCloud container listening on port 8080 using Docker.
• Execute the following command to create the ownCloud Docker container.

$ docker run -d --name owncloud -p 8080:8080 owncloud/server

• Start ownCloud.

$ docker start owncloud

• Verify that ownCloud is running.

$ docker ps

3. Setup Apache as a Reverse Proxy

• Before making any changes, back up the default Apache virtual host configuration file.

$ sudo mv /etc/apache2/sites-available/000-default.conf  /etc/apache2/sites-available/origdefault.backup

• Create a new configuration file.

$ sudo nano /etc/apache2/sites-available/app.example.com.conf

• Update the file with the following, replacing app.example.com with your server’s domain name. If you’re using a different app, change port 8080 to its actual port number.

  <VirtualHost *:80>
    ServerName app.example.com
    ProxyPreserveHost On
    ProxyPass / http://127.0.0.1:8080/
    ProxyPassReverse / http://127.0.0.1:8080/
  </VirtualHost>

• Save and close the file.

Here’s what each directive in the configuration does:

• ProxyPreserveHost: Forwards the original host header to the backend server.
• ProxyPass: Routes all requests destined for the specified port to the backend application.
• ProxyPassReverse: Modifies response headers from the backend server to ensure they work with the reverse proxy.

• Enable the configuration file.

$ sudo ln -s /etc/apache2/sites-available/app.example.com.conf  /etc/apache2/sites-enabled/app.example.com.conf

• Test the Apache configuration for any errors.

$ sudo apachectl configtest

• Restart Apache to apply the changes.

$ sudo service apache2 restart

4. Secure The Server

• Configure the firewall to allow HTTP traffic on port 80.

$ sudo ufw allow 80/tcp

• Allow HTTPS traffic on port 443 as well.

sudo ufw allow 443/tcp

• Reload the firewall to apply these changes.

sudo ufw reload

5. Setup SSL Certificate

• Install Certbot.

$ sudo apt install certbot python3-certbot-apache

• Request a Let’s Encrypt SSL Certificate.

$ sudo certbot -d app.example.com

• Test Auto-renewal.

$ sudo certbot renew --dry-run

6. Testing Is Necessary

• Open your web browser and navigate to your subdomain:

https://app.example.com

• You should see the ownCloud login page. Use the username “admin” and the password “admin” to log in and start using the application.