Why Heroku Cleans Assets After Precompiling Them: A Deep Dive
Heroku's asset cleaning behavior after precompilation can be perplexing, especially for those new to the platform. Imagine this: you've meticulously precompiled your assets locally, ensuring everything is ready for deployment. Then, on Heroku, you see those same assets being deleted, replaced with a seemingly empty folder. This can lead to confusion and frustration.
This article aims to shed light on why Heroku cleans assets after precompilation and how to effectively manage this behavior.
Understanding the Scenario
Consider the following code snippet from your Procfile:
web: bundle exec rails server -p $PORT
This line tells Heroku to run your Rails application using the rails server command. Heroku will then precompile your assets using the assets:precompile rake task, as part of its deployment process. However, after precompilation, you might notice that the public/assets folder is empty.
Unraveling the Mystery: Heroku's Asset Management
The reason behind Heroku's asset cleaning is rooted in its streamlined asset management process. When you deploy your application, Heroku works behind the scenes to ensure a clean and efficient deployment experience.
Here's how it works:
- Precompilation: During deployment, Heroku automatically precompiles your assets (using
assets:precompilein the background) to ensure they are ready for production. - Cleaning Up: Immediately after precompilation, Heroku cleans up the
public/assetsdirectory, deleting any existing files. This step is crucial to prevent potential conflicts and ensure a clean slate for the compiled assets. - Deploying Compiled Assets: Heroku then deploys the precompiled assets from its internal cache into the
public/assetsdirectory on your application's server.
This process ensures that:
- Fresh Assets: Your application always runs with the most recent versions of your precompiled assets.
- Clean Environment: By cleaning the directory before deploying, potential conflicts are minimized.
- Efficiency: Using a cached asset directory allows Heroku to deploy your assets quickly and efficiently.
Overcoming the Perceived Problem
While the cleaning process might seem like a problem, it's actually a deliberate design choice that ensures smooth deployment and asset management. You don't need to manually clean the public/assets folder or precompile assets before deployment. Heroku handles this seamlessly for you.
Best Practices for Asset Management
- Use
assets:precompile: Make sure you are using theassets:precompilerake task to precompile your assets locally for development. This will ensure that your assets are properly prepared for deployment. - Keep
config.assets.compileFalse: In your production environment, setconfig.assets.compiletofalsein yourconfig/environments/production.rbfile. This will prevent unnecessary asset compilation on the Heroku server and will leverage Heroku's precompiled assets. - Avoid Precompiling Assets Locally Before Deploying: As discussed, Heroku handles asset precompilation and deployment internally. Precompiling assets locally before deployment can lead to conflicts and unnecessary complexity.
Conclusion
Heroku's asset cleaning behavior is a deliberate design choice aimed at optimizing deployment and asset management. By understanding its underlying principles and following best practices, you can ensure a smooth and efficient deployment process for your Rails applications on Heroku.
