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Edge Subdomain vs. CDN Proxy

This is the documentation for Performance Edge. If you'd like access, please reach out to your Optimizely account manager.

Edge Subdomain is the recommended way of implementing Performance Edge, but there are some situations where a CDN proxy may make more sense. We’ll compare how they do across multiple categories.

Implementation Difficulty

To implement Edge Subdomain, you’ll need to:

  • Pick and setup a subdomain
  • Add a CNAME record to your DNS records
  • Wait for Optimizely to update our infrastructure to securely support requests from your subdomain
    • The time for Optimizely to do this is usually within 2 business days
  • Add a script tag to your page

To implement via a CDN proxy:

  • Configure CDN to be able to forward requests from your visitor’s browsers to our Edge Decider
  • Add a script tag to your page

The core step in each process is italicized. For most customers, it will be easier to set up a subdomain and add a CNAME to their DNS records than to configure their CDN to forward requests.

This is because the latter is a more complex process with more configuration options but also more room for error.

For this reason, most customers will find that implementing Edge Subdomain will be easier than setting up a CDN proxy.

Performance

Edge Subdomain enables your visitor’s browsers to make a request directly to our Edge Decider and receive a microsnippet back directly. The only part of your infrastructure that is used is DNS.

In the CDN proxy option, requests are first forwarded to your CDN provider and then forwarded onto our Edge Decider. Responses are similarly forwarded by your CDN provider.

In our testing, we have found that the Edge Subdomain option performs just as well if not better than the CDN proxy solution since it reduces the number of hops and the latency induced by translating requests and responses. However, your experience may differ; if you are considering implementing Performance Edge you can use Optimizely Rollouts or a similar service to do an experiment.

Security

Both methods of implementing Performance Edge are secure. Our Edge Decider only responds with a microsnippet to requests made over HTTPS encrypted with TLS 1.2.

Since Edge Subdomain enables requests to be made directly to our Edge Decider while the CDN proxy makes requests through another service, your CDN provider, there is technically a higher risk of compromise with the CDN proxy, but this difference is minimal. Security should not be a factor in determining between using Edge Subdomain versus a CDN proxy.

Cookies

On every request to a particular domain, browsers send all cookies that that domain has access to. What this means is that using your subdomain to make the request gives Optimizely’s Edge Decider access to all the cookies that your subdomain has access to.

For some customers, this may be unacceptable especially if some of these cookies contain personal identifiers (e.g. name, email, address). The only cookies that Optimizely reads and uses are listed here as well as any cookies you target an audience with, but the Edge Decider will still have access to all the cookies your subdomain has access to.

A CDN proxy however can filter the cookies that are forwarded to the Edge Decider. One can set up an allowlist or denylist to control which cookies are forwarded.


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