Varnish Cache is a highly performant HTTP reverse Proxy cache server that can significantly accelerate website loading times by storing copies of pages served by the web server. When a user requests a page, Varnish first tries to find it in its cache; if found, it serves it to the user instead of sending the request to the web server. This can dramatically reduce page load times and server load. In this article, you will learn how to configure and utilize Varnish Cache on your Virtual private server (VPS) to speed up your website.

1. Installing Varnish Cache

The first step is to install Varnish Cache on your VPS. Most Linux distributions have Varnish available in their standard repositories. On Debian-based systems (such as Ubuntu), you can install Varnish using the following command:

sudo apt-get update && sudo apt-get install varnish

On Red Hat-based systems (e.g., CentOS), use:

sudo yum install varnish

2. Configuring Varnish Cache

After installation, Varnish needs to be configured. The main configuration files for Varnish are located in /etc/varnish/. The most important ones are:

• default.vcl: This file defines the rules for caching, including what requests to cache and how long to keep them.
• varnish.params: This file contains general Varnish settings, such as the port it listens on and the size of memory allocated for the cache.

Start by editing the default.vcl file. Here, you can define the backend, i.e., the web server from which Varnish retrieves content. An example configuration for Apache looks like this:

backend default {
    .host = "127.0.0.1";
    .port = "8080";
}

This setting assumes your web server is running on the localhost (127.0.0.1) on port 8080. Varnish should be set to listen on port 80, the standard HTTP port, to have all incoming web traffic pass through Varnish.

3. Setting up the Web Server

You also need to adjust your web server's configuration to listen on a different port since the standard port 80 will now be used by Varnish. For Apache, you can do this by editing the /etc/apache2/ports.conf file and relevant VirtualHost files, changing Listen 80 to Listen 8080.

4. Starting and Testing Varnish Cache

After configuring Varnish and the web server, restart both services. For Varnish, use:

sudo systemctl restart varnish

For Apache or another web server, use the appropriate command to restart the service.

To test if Varnish cache is working, you can use the curl tool with the X-Varnish header, which will be present in responses to requests for cached content. For example:

curl -I http://yourwebsite.com

If Varnish is properly configured and working, you should see the X-Varnish header in the response, indicating the request was processed by Varnish cache.

Varnish Cache is a powerful tool for speeding up your website, but it requires careful configuration and management. By regularly monitoring and adjusting the configuration to suit your website's needs, you can maximize the benefits Varnish offers.