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Serving Static Files

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Applications often need to serve static files such as JavaScript, images, and CSS in addition to handling dynamic requests. Apps in the flexible environment can serve static files from a Google Cloud option like Cloud Storage, serve them directly, or use a third-party content delivery network (CDN).

Serving files from Cloud Storage

Cloud Storage can host static assets for dynamic web apps. The benefits of using Cloud Storage instead of serving directly from your app include:

  • Cloud Storage essentially works as a content delivery network. This does not require any special configuration because by default any publicly readable object is cached in the global Cloud Storage network.
  • Your app's load will be reduced by offloading serving static assets to Cloud Storage. Depending on how many static assets you have and the frequency of access, this can reduce the cost of running your app by a significant amount.
  • Bandwidth charges for accessing content can often be less with Cloud Storage.

You can upload your assets to Cloud Storage by using the gsutil command line tool or the Cloud Storage API.

The Google Cloud Client Library provides an idiomatic Ruby client to Cloud Storage, for storing and retrieving data with Cloud Storage in an App Engine app.

Example of serving from a Cloud Storage bucket

This simple example creates a Cloud Storage bucket and uploads static assets using Google Cloud CLI:

  1. Create a bucket. It's common, but not required, to name your bucket after your project ID. The bucket name must be globally unique.

    gsutil mb gs://<your-bucket-name>
  2. Set the ACL to grant read access to items in the bucket.

    gsutil defacl set public-read gs://<your-bucket-name>
  3. Upload items to the bucket. The rsync command is typically the fastest and easiest way to upload and update assets. You could also use cp.

    gsutil -m rsync -r ./static gs://<your-bucket-name>/static

You can now access your static assets via<your-bucket-name>/static/....

For more details on how to use Cloud Storage to serve static assets, including how to serve from a custom domain name, refer to How to Host a Static Website.

Serving files from other Google Cloud services

You also have the option of using Cloud CDN or other Google Cloud storage services.

Serving files directly from your app

Serving files from your app is typically straightforward, however, there are a couple drawbacks that you should consider:

  • Requests for static files can use resources that otherwise would be used for dynamic requests.
  • Depending on your configuration, serving files from your app can result in response latency, which can also affect when new instances are created for handling the load.

Example of serving static files with your app

Most web frameworks include support for serving static files.


The Sinatra web framework serves files from the ./public directory by default. This app includes a view that refers to /application.css.

doctype html
    title Serving Static Files
    link rel="stylesheet" href="/application.css"
    script src="/application.js"
    p This is a static file serving example.

The stylesheet is located at ./public/application.css which is served from /application.css.

body {
  font-family: Verdana, Helvetica, sans-serif;
  background-color: #CCCCFF;

Ruby on Rails

The Ruby on Rails web framework serves files from the ./public directory by default. Static JavaScript and CSS files can also be generated by the Rails asset pipeline.

This example app has a layout view that includes all the app's stylesheets:

doctype html
    title Serving Static Files
    = stylesheet_link_tag "application", media: "all"
    = javascript_include_tag "application"
    = csrf_meta_tags
    = yield

The stylesheet itself is a Sass file located at ./app/assets/stylesheets/main.css.sass.

  font-family: Verdana, Helvetica, sans-serif
  background-color: #CCCCFF

By default, Rails apps do not generate or serve static assets when running in production.

The Ruby runtime executes rake assets:precompile during deployment to generate static assets and sets the RAILS_SERVE_STATIC_FILES environment variable to enable static file serving in production.

Serving from a third-party content delivery network

You can use any external third-party CDN to serve your static files and cache dynamic requests but your app might experience increased latency and cost.

For improved performance, you should use a third-party CDN that supports CDN Interconnect.