Learn how to configure a CDN with Galaxy

Configuring a CDN with Galaxy is largely the same as using a CDN with Meteor in any context.

In general, you don’t want to forward cookies from your CDN, as it leads to overcaching. Specifically, you should not forward the galaxy-sticky cookie, as it will result in caching one copy of every asset per container that your application runs. However, you do want to configure your CDN to forward query string parameters.

Once you’ve set up the CDN with your application as its origin (for example, a CloudFront distribution named which proxies for, you can tell Meteor to serve static JS and CSS assets from the CDN with

WebAppInternals.setBundledJsCssUrlRewriteHook((url) => {
  return `${url}&_g_app_v_=${process.env.GALAXY_APP_VERSION_ID}`;

The _g_app_v_ query parameter tells Galaxy to only send this request to containers running the same version as the container that served the app HTML to you. Since different versions of your app are likely to have different versions of JS and CSS (and thus different bundled filenames), you want to ensure that the CDN looks at a container that will actually contain the file in question.

This isn’t a concern without a CDN, because Galaxy uses cookies to ensure that the JS/CSS request is routed to the same container as the HTML if possible, and Meteor knows to refresh the whole page if that’s no longer possible. But because you should not configure your CDN to forward cookies, the normal mechanism does not work and the _g_app_v_ technique is necessary.

If you have static assets such as images used in your templates (for example <img src="foo.png" />) that you would also like to have cached by the CDN, you’ll need to include the CDN prefix and _g_app_v_ query parameter in the image tag too. Combined with the previous example, the image would tag become <img src="{process.env.GALAXY_APP_VERSION_ID}" />. We recommend you create a helper that does this for you only in production.

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