Rails 6 Heroku Asset Compilation: A Comprehensive Guide

Are you tired of dealing with asset compilation issues when deploying your Rails 6 app to Heroku? Well, you’re in luck! In this article, we’ll take you by the hand and walk you through the process of setting up Rails 6 Heroku asset compilation like a pro.

What is Asset Compilation, Anyway?

Before we dive into the nitty-gritty, let’s take a step back and understand what asset compilation is all about. In Rails, assets refer to static files like images, CSS, and JavaScript files that are used to style and script our application. Asset compilation is the process of taking these individual files and combining them into a single, production-ready file that can be served to users.

Why Do We Need Asset Compilation?

There are several reasons why asset compilation is essential for Rails applications:

• Faster Load Times: By combining multiple files into one, we can reduce the number of HTTP requests, resulting in faster page loads.
• Improved Performance: Compression and minification of assets can reduce the overall file size, making it easier for users to download and render.
• Easier Maintenance: Asset compilation allows us to manage our assets in a modular fashion, making it easier to update and maintain individual files.

Rails 6 Asset Compilation: The Basics

In Rails 6, asset compilation is handled by the `sprockets` gem. Sprockets provides a way to concatenate, compress, and version assets. By default, Rails 6 comes with Sprockets 4, which includes support for modern features like Webpack and JavaScript modules.

Configuring Asset Compilation

To configure asset compilation in Rails 6, we need to create a `config/initializers/assets.rb` file with the following content:

Rails.application.config.assets.version = '1.0'
Rails.application.config.assets.precompile += %w( admin.css admin.js )

This file tells Rails to version our assets and include additional files (in this case, `admin.css` and `admin.js`) in the asset compilation process.

Heroku Asset Compilation: The Gotchas

Now that we’ve covered the basics of asset compilation in Rails 6, let’s talk about the challenges we face when deploying to Heroku.

Heroku’s Asset Compilation Process

When we deploy our Rails app to Heroku, the platform takes care of asset compilation for us. However, this process can be slow and may lead to errors if not configured correctly. Heroku uses a combination of `rake assets:precompile` and `rake assets:clean` to compile and serving our assets.

Common Issues with Heroku Asset Compilation

Here are some common issues you might encounter when dealing with Heroku asset compilation:

• SLOW_COMPILATION: If your asset compilation takes too long, Heroku may timeout, resulting in failed deployments.
• ASSET_COMPILATION_ERRORS: Errors during asset compilation can prevent your app from deploying successfully.
• UNUSED_ASSETS: Failing to declare unused assets can lead to bloated asset files and slow load times.

Optimizing Heroku Asset Compilation for Rails 6

Now that we’ve covered the potential pitfalls, let’s dive into some best practices for optimizing Heroku asset compilation for Rails 6:

1. Use a `manifest.json` file

In Rails 6, we can use a `manifest.json` file to declare our assets and their dependencies. This file tells Sprockets which assets to compile and in what order.

{
  "files": {
    "application.js": {
      " dependencies": ["admin.js"]
    }
  }
}

This `manifest.json` file tells Sprockets to compile `application.js` and include `admin.js` as a dependency.

2. Use `rake assets:precompile` wisely

`rake assets:precompile` is a powerful command that can be used to precompile our assets locally before deploying to Heroku. However, it can also lead to slow compilation times and errors.

Instead, use `rake assets:precompile` with caution and only when necessary. For example, you can use it to precompile assets for a specific environment (e.g., production) or to precompile a specific set of assets.

3. Leverage Heroku’s Built-in Asset Compilation

Heroku provides a built-in asset compilation feature that can be enabled by setting the `RAILS_SERVE_STATIC_FILES` environment variable to `enabled`.

heroku config:set RAILS_SERVE_STATIC_FILES=enabled

This will tell Heroku to serve static assets directly, bypassing the need for asset compilation during deployment.

4. Use a CDN for Assets

Using a CDN (Content Delivery Network) can significantly improve asset load times by distributing assets across multiple servers. Heroku provides built-in support for CDNs like CloudFront and Fastly.

5. Monitor and Optimize Asset Compilation

Use tools like New Relic or Rollbar to monitor asset compilation times and identify bottlenecks. Optimize your asset compilation process by reducing the number of assets, minifying and compressing files, and leveraging browser caching.

Conclusion

Rails 6 Heroku asset compilation can be a complex and daunting task, but with the right approach, it can be a breeze. By following the best practices outlined in this article, you can optimize your asset compilation process, reduce deployment times, and improve overall application performance.

Final Checklist

Before deploying your Rails 6 app to Heroku, make sure to:

1. Configure asset compilation in `config/initializers/assets.rb`
2. Use a `manifest.json` file to declare assets and dependencies
3. Optimize asset compilation with `rake assets:precompile`
4. Leverage Heroku’s built-in asset compilation
5. Use a CDN for assets
6. Monitor and optimize asset compilation

By following this checklist, you’ll be well on your way to mastering Rails 6 Heroku asset compilation.

Asset Compilation Best Practice	Description
Use a `manifest.json` file	Declare assets and dependencies for Sprockets
Optimize `rake assets:precompile`	Use `rake assets:precompile` wisely to reduce compilation times
Leverage Heroku’s built-in asset compilation	Enable `RAILS_SERVE_STATIC_FILES` for Heroku to serve static assets
Use a CDN for assets	Distribute assets across multiple servers for faster load times
Monitor and optimize asset compilation	Use tools like New Relic or Rollbar to monitor and optimize asset compilation

Happy deploying!

Frequently Asked Question

Having trouble with Rails 6 Heroku asset compilation? Don’t worry, we’ve got you covered! Here are some frequently asked questions to help you troubleshoot common issues: