Page caching combined with Varnish can significantly boost the performance and scalability of web applications by serving cached pages directly from memory. In this article, we’ll explore how to utilize page caching in Rails along with Varnish as a reverse proxy cache to achieve optimal performance.

I. Understanding Page Caching and Varnish

Page Caching: Page caching involves storing the entire HTML output of a page and serving it directly from cache for subsequent requests. It eliminates the need to regenerate the page dynamically, resulting in faster response times and reduced server load.

Varnish: Varnish is an open-source, high-performance reverse proxy cache. It sits in front of web servers and caches HTTP responses, serving cached content to clients without hitting the backend server. Varnish is known for its ability to handle large volumes of traffic and improve the overall responsiveness of web applications.

III. Implementation Steps

1. Configure Page Caching in Rails

Enable page caching in your Rails application by adding the following line to your controller:

class PagesController < ApplicationController
  caches_page :index, :show
end

This instructs Rails to cache the index and show actions of the PagesController.

2. Install and Configure Varnish

Install Varnish on your server and configure it to listen on port 80. Consult the official Varnish documentation for detailed installation instructions specific to your operating system.

3. Configure Varnish to Cache Requests

Edit the Varnish configuration file (/etc/varnish/default.vcl) to define caching rules. Below is a basic example configuration to cache all GET requests:

vcl 4.0;

backend default {
    .host = "127.0.0.1";
    .port = "3000";
}

sub vcl_recv {
    if (req.method == "GET") {
        return (hash);
    }
}

sub vcl_backend_response {
    if (bereq.method == "GET" && beresp.status == 200) {
        set beresp.ttl = 1h;
    }
}

This configuration tells Varnish to cache all GET requests for 1 hour.

4. Restart Varnish and Rails Server

After configuring Varnish, restart the Varnish service to apply the changes. Also, restart your Rails server to ensure that Rails caching is enabled.

sudo systemctl restart varnish

rails server

IV. Conclusion

By combining page caching in Rails with Varnish as a reverse proxy cache, we’ve created a powerful caching mechanism that significantly improves the performance and scalability of web applications. Page caching reduces server load by serving pre-generated HTML pages directly from cache, while Varnish further optimizes performance by caching HTTP responses and serving cached content to clients. This approach ensures faster response times, reduced server load, and improved user experience, making it an essential technique for optimizing web applications in production environments.