How to Configure Apache as a Reverse Proxy with mod_proxy

Learn how to configure Apache as a reverse proxy with mod_proxy, perfect for hosting applications like ownCloud.

Introduction

Apache is a web server application that can serve dynamic web content or act as a reverse proxy —forwarding client requests to back-end applications. This article explains how to configure Apache as a reverse proxy with mod_proxy.

This guide proxies an ownCloud application on port 8080 under Docker, but you can use the same technique to host another application on a different port.

Prerequisites

Deploy a fresh Vultr Cloud Server.

A Ubuntu 20.04 server is used in this article, but these instructions work for any Linux server 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 Apache mod_Proxy

Enable the Apache mod_proxy module.
```
$ sudo a2enmod proxy
```
Enable additional modules.
```
$ sudo a2enmod proxy_http
$ sudo a2enmod proxy_balancer
$ sudo a2enmod proxy_wstunnel
```
Here is what each module does:
- mod_proxy: Implements proxying on the Apache server.
- proxy_http: Handles proxy HTTP and HTTPS requests.
- proxy_balancer: Enables load balancing.
- proxy_wstunnel: Tunnels web socket connections to a back-end server.
Restart Apache to activate modules.
```
$ sudo systemctl restart apache2
```

2. Set up the Back-end Application

As an example, set up an ownCloud container listening on port 8080 under Docker.

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

Output:

  CONTAINER ID   IMAGE             COMMAND                  CREATED          STATUS          PORTS                                       NAMES
  3eaea7b55cfe   owncloud/server   "/usr/bin/entrypoint…"   36 seconds ago   Up 35 seconds   0.0.0.0:8080->8080/tcp, :::8080->8080/tcp   owncloud

3. Configure Apache as a Reverse Proxy

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

Add the following contents to the file. Change app.example.com to your server name. If you are setting up a proxy for a different app than the ownCloud example, you may need to update port 8080 to your application’s port number in the file below.
```
  <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 is what each directive means:
- ProxyPreserveHost: Forwards the original host header to the back-end application.
- ProxyPass: Specifies that all requests / are forwarded to the back-end application port.
- ProxyPassReverse: Negates ProxyPass by modifying response headers from the back-end application.

Activate 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 errors.
```
$ sudo apachectl configtest
```
Restart Apache to load 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 on port 443.
```
$ sudo ufw allow 443/tcp
```
Restart the firewall.
```
$ sudo ufw reload
```

5. Setup SSL

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. Test

Open a web browser, and visit your subdomain.

 https://app.example.com

The ownCloud login page should be displayed. Log in with the username admin, and password admin to start using the application.

More Information

You have configured Apache as a reverse proxy and set up ownCloud as the back-end application. For further information, refer to the following resources.

Apache mod_proxy documentation.
Use Apachetop To Monitor Web Server Traffic In Real Time.
Secure Apache with a Self-Signed TLS/SSL Certificate on Ubuntu 20.04.

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