configassetscompiletrue in Rails production why not

Deploying a Rails application to production is a significant step, and optimizing its performance is critical for a smooth user experience. One of the most common questions that arises during this process is whether to enable config.assets.compile=true. While seemingly convenient, keeping config.assets.compile set to true in your production environment can lead to significant performance bottlenecks and operational headaches. This setting, designed for development environments where assets are frequently changed, dynamically compiles assets on each request. In a production setting, this can severely impact response times, increase server load, and create unnecessary dependencies. We’ll explore why this practice is generally discouraged and delve into the best practices for managing assets in a production Rails application, ensuring optimal performance and scalability. Understanding the nuances of asset compilation, precompilation, and delivery mechanisms is paramount for any Rails developer aiming to build robust and efficient applications.

Why Avoiding config.assets.compile=true in Production is Crucial

The primary reason to avoid config.assets.compile=true in your Rails production environment stems from its performance implications. When this setting is enabled, your Rails application dynamically compiles assets (like CSS and JavaScript) every time they are requested. This compilation process consumes significant server resources, including CPU and memory, leading to slower response times for your users. Imagine a scenario where hundreds or thousands of users simultaneously request the same asset; your server would be forced to recompile that asset repeatedly, causing a massive strain. This can result in a degraded user experience, increased server costs, and potential application instability.

Moreover, relying on dynamic asset compilation in production introduces unnecessary dependencies. Your production servers would need to have the necessary gems and executables (such as the JavaScript runtime) installed to perform the compilation. This adds complexity to your deployment process and increases the risk of encountering dependency-related issues. Using a precompiled assets approach greatly simplifies the deployment process and reduces the burden on production servers. This method not only improves performance but also contributes to a more stable and predictable environment. The performance hit is simply too significant to justify the convenience, especially when better alternatives exist.

According to a study by Google, 53% of mobile site visitors leave a page that takes longer than three seconds to load [1]. By enabling config.assets.compile=true, you are directly contributing to slower load times and potentially losing a significant portion of your audience. Optimization is key when addressing web app performance issues.

Understanding Asset Precompilation in Rails

Asset precompilation is the recommended approach for managing assets in a Rails production environment. Instead of dynamically compiling assets on each request, precompilation involves compiling them once during the deployment process. This generates static asset files that can be served directly by your web server (such as Nginx or Apache) or a Content Delivery Network (CDN). This approach significantly reduces the load on your Rails application servers, as they no longer need to handle asset compilation. Precompilation is handled by the rails assets:precompile task, which leverages the asset pipeline to bundle and minify your CSS, JavaScript, and other assets.

The precompiled assets are typically stored in the public/assets directory. Your web server is then configured to serve these static files directly, bypassing the Rails application for asset requests. This results in much faster response times and improved scalability. Furthermore, precompilation allows you to leverage CDNs to cache and deliver your assets from geographically distributed servers, further enhancing performance for users around the world. This is a key factor in providing a consistently fast user experience, regardless of location. The precompilation process also allows for fingerprinting of assets, which enables aggressive browser caching and ensures that users always receive the latest version of your assets after a deployment.

To precompile assets, you typically run the command RAILS_ENV=production rails assets:precompile during your deployment process. Tools like Capistrano and other deployment automation tools can handle this step automatically. Make sure that config.assets.compile is set to false in your config/environments/production.rb file to ensure that assets are not dynamically compiled at runtime. Asset precompilation aligns with best practices in web performance optimization. By precompiling assets and serving them directly from a web server or CDN, you minimize the overhead on your Rails application, resulting in faster load times and improved scalability. This is a fundamental aspect of building a production-ready Rails application.

Configuring Your Web Server and CDN for Optimal Asset Delivery

Once you’ve precompiled your assets, the next step is to configure your web server and CDN to efficiently deliver them to your users. Most web servers, such as Nginx and Apache, are highly optimized for serving static files. You should configure your web server to serve the files in the public/assets directory directly, bypassing the Rails application. This can be achieved by adding a location block in your web server configuration that maps requests for /assets to the public/assets directory.

Leveraging a CDN can further enhance asset delivery by caching your assets on geographically distributed servers. When a user requests an asset, the CDN serves it from the server closest to their location, minimizing latency and improving load times. Popular CDN providers include Cloudflare, Amazon CloudFront, and Fastly. Configuring a CDN typically involves uploading your assets to the CDN and updating your application to use the CDN’s URLs for your assets. Rails provides built-in support for CDNs through the config.action_controller.asset_host configuration option. Setting this option to your CDN’s URL will automatically generate asset URLs that point to your CDN.

Properly configuring your web server and CDN is essential for maximizing the benefits of asset precompilation. By serving assets directly from your web server or CDN, you minimize the load on your Rails application and ensure that your users receive the fastest possible experience. This is a critical step in optimizing the performance and scalability of your Rails application. According to Amazon CloudFront’s pricing page, using a CDN can significantly reduce your bandwidth costs while simultaneously improving performance [2].

Best Practices for Asset Management in Rails Production

Here are some best practices to keep in mind when managing assets in your Rails production environment:

• Always precompile your assets during deployment.
• Set config.assets.compile to false in your config/environments/production.rb file.
• Configure your web server to serve static assets directly.
• Leverage a CDN for global asset delivery.
• Use asset fingerprinting to enable aggressive browser caching.
• Monitor your asset delivery performance using tools like Google PageSpeed Insights.

Troubleshooting Common Asset-Related Issues -------------------------------------------

Even with careful planning, you might encounter issues related to asset management in your Rails production environment. One common problem is missing assets after deployment. This can occur if the rails assets:precompile task was not executed correctly or if the assets were not properly deployed to your web server or CDN. To troubleshoot this, verify that the public/assets directory contains the expected asset files and that your web server or CDN is configured to serve them correctly. Check your deployment logs for any errors related to asset precompilation or deployment.

Another common issue is outdated assets being served to users. This can happen if browser caching is not properly configured or if asset fingerprinting is not enabled. To resolve this, ensure that your web server is sending appropriate cache-control headers for your assets and that asset fingerprinting is enabled in your Rails application. You can also try clearing your browser cache or performing a hard refresh to force the browser to download the latest version of the assets.

If you’re using a CDN, ensure that your CDN’s cache is properly configured and that you have a mechanism for invalidating the cache when you deploy new assets. Most CDN providers offer APIs or web interfaces for invalidating the cache for specific assets or entire directories. By proactively addressing these potential issues, you can ensure a smooth and reliable asset delivery experience for your users. Remember to thoroughly test your asset deployment process in a staging environment before deploying to production. For further assistance, consider reviewing the official Rails documentation or seeking help from the Rails community. You can also find valuable resources and tutorials online that cover various aspects of asset management in Rails.

FAQ: Asset Compilation in Rails Production

Why is `config.assets.compile=true` bad for production?

It dynamically compiles assets on every request, causing slow response times and high server load.

What is asset precompilation?

Compiling assets once during deployment and serving them as static files.

How do I precompile assets in Rails?

Run `RAILS_ENV=production rails assets:precompile` during your deployment process.

What is a CDN and why should I use one?

A Content Delivery Network caches assets on geographically distributed servers, reducing latency for users.

How do I configure my web server to serve static assets?

Configure your web server to serve files in the `public/assets` directory directly, bypassing the Rails application.

Enabling `config.assets.compile=true` in a Rails production environment is a recipe for performance disaster. The overhead of dynamically compiling assets on each request is simply too high, leading to slow response times, increased server load, and a degraded user experience. The recommended approach is to precompile your assets during deployment and serve them as static files through your web server or a CDN. This not only improves performance but also simplifies your deployment process and reduces the risk of encountering dependency-related issues. Remember, optimizing asset delivery is a crucial aspect of building a robust and scalable Rails application. By following the best practices outlined in this guide, you can ensure that your users enjoy a fast and seamless experience.

Ready to take your Rails application’s performance to the next level? Start by ensuring that config.assets.compile is set to false in your production environment and implement a robust asset precompilation and delivery strategy. Explore CDNs to distribute your assets globally and monitor your application’s performance to identify areas for further optimization. For more on improving application performance, check out our guide on Rails performance tuning and other optimization strategies. Taking these steps will help ensure a fast and reliable user experience, contributing to the overall success of your application.

Featured Snippet: One of the most effective ways to improve Rails application performance in production is by disabling dynamic asset compilation. Setting config.assets.compile to false and precompiling assets during deployment ensures that static files are served directly, reducing server load and improving response times. This optimization is a fundamental step in building a scalable and efficient Rails application.

• Disable dynamic asset compilation for improved performance.
• Precompile assets during deployment to create static files.

According to research by Akamai, even a 100-millisecond delay in website load time can hurt conversion rates by 7% [3]. Don’t let asset compilation be the bottleneck.

Question & Answer :
The default Rails app installed by rails new has config.assets.compile = false in production.

And the ordinary way to do things is to run rake assets:precompile before deploying your app, to make sure all asset pipeline assets are compiled.

So what happens if I set config.assets.compile = true in production?

I wont’ need to run precompile anymore. What I believe will happen is the first time an asset is requested, it will be compiled. This will be a performance hit that first time (and it means you generally need a js runtime in production to do it). But other than these downsides, after the asset was lazily compiled, I think all subsequent access to that asset will have no performance hit, the app’s performance will be exactly the same as with precompiled assets after this initial first-hit lazy compilation. is this true?

Is there anything I’m missing? Any other reasons not to set config.assets.compile = true in production? If I’ve got a JS runtime in production, and am willing to take the tradeoff of degraded performance for the first access of an asset, in return for not having to run precompile, does this make sense?

I wrote that bit of the guide.

You definitely do not want to live compile in production.

When you have compile on, this is what happens:

Every request for a file in /assets is passed to Sprockets. On the first request for each and every asset it is compiled and cached in whatever Rails is using for cache (usually the filesystem).

On subsequent requests Sprockets receives the request and has to look up the fingerprinted filename, check that the file (image) or files(css and js) that make up the asset were not modified, and then if there is a cached version serve that.

That is everything in the assets folder and in any vendor/assets folders used by plugins.

That is a lot of overhead as, to be honest, the code is not optimized for speed.

This will have an impact on how fast asset go over the wire to the client, and will negatively impact the page load times of your site.

Compare with the default:

When assets are precompiled and compile is off, assets are compiled and fingerprinted to the public/assets. Sprockets returns a mapping table of the plain to fingerprinted filenames to Rails, and Rails writes this to the filesystem. The manifest file (YML in Rails 3 or JSON with a randomised name in Rails 4) is loaded into Memory by Rails at startup and cached for use by the asset helper methods.

This makes the generation of pages with the correct fingerprinted assets very fast, and the serving of the files themselves are web-server-from-the-filesystem fast. Both dramatically faster than live compiling.

To get the maximum advantage of the pipeline and fingerprinting, you need to set far-future headers on your web server, and enable gzip compression for js and css files. Sprockets writes gzipped versions of assets which you can set your server to use, removing the need for it to do so for each request.

This get assets out to the client as fast as possible, and in the smallest size possible, speeding up client-side display of the pages, and reducing (with far-future header) requests.

So if you are live compiling it is:

1. Very slow
2. Lacks compression
3. Will impact render time of pages

Versus

1. As fast as possible
2. Compressed
3. Remove compression overheard from server (optionally).
4. Minimize render time of pages.

Edit: (Answer to follow up comment)

The pipeline could be changed to precompile on the first request but there are some major roadblocks to doing so. The first is that there has to be a lookup table for fingerprinted names or the helper methods are too slow. Under a compile-on-demand senario there would need to be some way to append to the lookup table as each new asset is compiled or requested.

Also, someone would have to pay the price of slow asset delivery for an unknown period of time until all the assets are compiled and in place.

The default, where the price of compiling everything is paid off-line at one time, does not impact public visitors and ensures that everything works before things go live.

The deal-breaker is that it adds a lot of complexity to production systems.

[Edit, June 2015] If you are reading this because you are looking for a solution for slow compile times during a deploy, then you could consider precompiling the assets locally. Information on this is in the asset pipeline guide. This allows you to precompile locally only when there is a change, commit that, and then have a fast deploy with no precompile stage.