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Using a CDN

You can add a CDN in between your GrowthBook SDKs and your GrowthBook API Server. This will act as a caching layer when serving feature flags and enable virtually limitless scaling with very low maintenance costs.

All major CDNs are supported including Cloudflare, Fastly, Akamai, CloudFront, Azure Front Door, and Google Cloud CDN.

Using a CDN is a quick and easy solution to scaling. If you want more power and control, we recommend deploying our GrowthBook Proxy Server instead.

note

GrowthBook Cloud provides its own CDN for free for low/medium traffic apps (less than 10 million requests per month). If you plan to go above that limit, this guide will work for you as well. Just use https://cdn.growthbook.io as your Origin instead of a self-hosted GrowthBook API server.

How it Works​

  1. Add a CDN that sits in front of your GrowthBook API server
  2. Configure the CDN to cache requests to /api/features/* (and deny all other routes)
  3. Point your SDKs to your CDN's domain instead of your GrowthBook API Server
  4. (optional) Configure a Webhook to invalidate the CDN cache when features change within GrowthBook

Configuring your CDN​

Caching Rules​

The /api/features/* route includes a default Cache-control header that should work out-of-the-box for most CDNs:

public, max-age=30, stale-while-revalidate=3600, stale-if-error=36000

This will serve all requests from cache and refresh in the background every 30 seconds. You can override these settings in your CDN if desired.

Important: Make sure to block all other routes besides /api/features/*. Doing this will greatly increase security by limiting the potential attack surface.

Health Checks​

The GrowthBook API server exposes a /healthcheck route. You can optionally use this in your CDN so it can tell if your origin server goes down.

SDK Configuration​

Most of our SDKs accept an apiHost setting. Simply change this from your GrowthBook API server to the new CDN domain.

Purging / Invalidation​

When you make changes withing GrowthBook, the CDN will not pick up the changes until it refreshes its cache (default 30 seconds).

For most apps, this short delay is perfectly fine. If you want faster rollouts, you can have GrowthBook tell your CDN to refresh as soon as changes are made.

Fastly​

If you use Fastly as your CDN and are self-hosting GrowthBook, you can set the following environment variables to automatically purge URLs:

  • FASTLY_SERVICE_ID
  • FASTLY_API_TOKEN

HTTP PURGE Requests​

If your CDN supports invalidaing URLs with simple HTTP PURGE requests, you can add an SDK Webhook in GrowthBook and set the method as PURGE with no payload.

Other​

If the methods above are not available for your CDN, you can configure a custom SDK Webhook. We let you customize the HTTP method and headers, but if you need more control, you may need to set up a custom script that sits between the webhook and the CDN.