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JavaScript & Assets


Assets require a Custom Domain Name to link properly when using API Gateway.

Some might remember a process where precompiling Rails CSS & JavaScript assets meant having Node and other dependencies installed on our production servers. In contrast, using container practices which embrace a multi-stage build process only has Node.js installed on the build image. Compiled assets along with other application code and dependencies are copied to the final production ECR image. This helps keep the production image small and secure.

CSS & JavaScript Ready!

Our Quick Start cookiecutter project is ready to hit the ground running with all the latest Rails defaults for JavaScript & CSS development. We do this by adding Node.js to the development container which is also used to build your production image. See our How Lamby Works guide for details.

For example, we can add the TailwindCSS Rails gem, run the ./bin/rails tailwindcss:install command, and edit the temporary starter index page like so. Once redeployed, we should see our Hello TailwindCSS page working correctly.

gem 'tailwindcss-rails'
<h1 class="
">Hello TailwindCSS</h1>
TailwindCSS on Rails on LambdaTailwindCSS on Rails on Lambda

Serving Static Assets

Our Quick Start cookiecutter project leverages Rails' built in ability to serve static assets. We do this by setting this environment variable in your Dockerfile.


We also add this configuration to your config/environments/production.rb file. In this case we are setting the cache control to 30 days, which you can change. The X-Lamby-Base64 header signals to the Lamby rack adapter that the content requires base64 binary encoding.

config.public_file_server.headers = {
'Cache-Control' => "public, max-age=#{30.days.seconds.to_i}",
'X-Lamby-Base64' => '1'

Using CloudFront

CloudFront is an amazing CDN and is pretty easy to setup with Rails. No crazy S3 bucket is needed. Simply point CloudFront to your Rails app and allow the origin to set the cache headers. Because we set the public_file_server headers above, everything should work out perfectly.