TLS encryption for CDN traffic

  • Updated
  • Optimizely Web Experimentation
  • Optimizely Personalization

Optimizely Web Experimentation and Optimizely Personalization use Transport Layer Security (TLS) for 100% of CDN traffic to protect against Man In The Middle attacks and meet customer compliance requirements. 

Performance and security

Optimizely works to minimize the impact of TLS on both CPU and performance. For more details, see TLS has exactly one performance problem: it is not used widely enough.

Optimizely TLS encryption is highly secure, maintaining an A grade from SSLLabs.


Optimizely's CDN sends the HSTS header. This header informs clients to connect to over HTTPS regardless of whether it is using the http:// or https:// URL. Performance impact should be negligible, due to the TLS optimizations in use.


Customers who have PCI-enabled accounts and load their assets from have all of their assets served over TLS.


Ciphersuites are reviewed at least annually and updated to address security risks and meet PCI compliance requirements for TLS.

Opting out of TLS

Optimizely has an alternative CDN available at for customers who want to opt-out of TLS. This domain points to Optimizely's same primary CDN but does not send the HSTS header. To transition to this CDN, change your URLs to point to

For information on how to change your URLS to cdn-s-optional, see Implement the one-line JavaScript snippet and change <script src="// to <script src="//

If you have any questions, contact your Customer Success Manager.