Dev guideAPI Reference
Dev guideAPI ReferenceUser GuideGitHubNuGetDev CommunitySubmit a ticketLog In
GitHubNuGetDev CommunitySubmit a ticket

Cloudflare Workers

Template hosted in GitHub for running Optimizely Feature Experimentation feature flags and experiments on Cloudflare Workers.

Cloudflare Workers provide a serverless execution environment that lets you create or augment existing applications without configuring or maintaining infrastructure.

Advantages of Cloudflare Workers

  • Automatic scaling – Traffic is automatically routed and load balanced across servers.

  • High-performance global network – Your code is powered by Cloudflare's global network.

  • Multiple programming languages – You can write in JavaScript, Rust, C, and C++.

  • No cold starts – Cloudflare supports 0 MS cold starts.



Although you can write Cloudflare Workers code in various languages, Optimizely currently only provides a template for JavaScript.

Cloudflare Workers use cases

See Cloudflare Examples documentation.

Restrictions and limitations

Cloudflare Workers have different plan limits and restrictions based on your account. See the official Cloudflare Limit documentation.

Optimizely + Cloudflare Worker template

The Optimizely Feature Experimentation Cloudflare Workers template embeds and extends the Javascript Node SDK to provide a starting point for you to implement experimentation and feature flagging for your experiences at the edge. For a general guide to getting started with Optimizely, see the Javascript SDK Quickstart.

Caching with Cloudflare

This template uses Cloudflare cache API to provide performant caching for the datafile.

Identity management

Optimizely's Feature Experimentation SDKs require passing a user-provided identifier at runtime to drive experiment and feature flag decisions. This example generates a unique ID, stores it in a cookie, and reuses it to make the decisions sticky. Alternatively, you can use an existing unique identifier available within your application and pass it in as the value for the OPTIMIZELY_USER_ID cookie.


See How bucketing works.

How to use


Get started

  1. Generate a project using the template hosted on GitHub:
    wrangler generate projectname
  2. Add account_id in wrangler.toml. If you do not know the account ID, type in wrangler whoami and you will see the account ID listed.
  3. Install node nodules.
    npm install
  4. Update your Optimizely Feature Experimentation sdkKey, flagKey and userId in src/index.js. Your SDK keys are in the Optimizely application under Settings.
  5. Test and debug the worker locally:
    wrangler dev
  6. Deploy the worker on Cloudflare:
    wrangler publish
  7. (Optional) Tail the logs for debugging when accessing workers deployed on Cloudflare:
    wrangler tail -f pretty

Additional resources