Enabling asset compilation in production environments creates significant performance problems for Rails applications.
When config.assets.compile = true is set in production, the Rails asset pipeline compiles assets on-demand during runtime. This means
every request for a CSS, JavaScript, or image file must be processed by Sprockets, the Rails asset compilation engine.
This live compilation approach has several serious drawbacks:
- Performance overhead: Each asset request requires compilation processing, adding latency to page loads
- Server resource consumption: The compilation process uses CPU and memory resources that should be dedicated to serving user
requests
- Missing optimizations: Live compilation bypasses important production optimizations like asset minification, compression, and
fingerprinting
- Caching issues: Dynamically compiled assets are harder to cache effectively, both on the server and in browsers
- Deployment complexity: Production servers need development dependencies like JavaScript runtimes for compilation
The Rails framework defaults to config.assets.compile = false in production for good reason. Assets should be precompiled during the
deployment process using rake assets:precompile, which creates optimized, compressed, and fingerprinted versions that can be served
efficiently by web servers.
What is the potential impact?
Applications with asset compilation enabled in production will experience slower page load times, increased server resource usage, and reduced
scalability. Users will face longer wait times when loading pages, especially those with many CSS and JavaScript files. The server will consume more
CPU and memory for asset processing instead of handling user requests, potentially leading to performance bottlenecks under load.
