Understanding the problem
The Vercel CDN was designed to carefully perform new releases of your application without downtime. Therefore, once a new production deployment is ready, we will purge our cache globally and replace the current deployment being served at your production domain with the new version.
If you use a CDN on top of Vercel, you may experience issues since our infrastructure cannot control those providers. A new release on Vercel can cause other CDNs to serve stale content referencing files that no longer exist. You can see an example of the issue below:
![Overview of possible issues sites using another CDN on top of Vercel may introduce to users.](/_next/image?url=https%3A%2F%2Fimages.ctfassets.net%2Fe5382hct74si%2F5yFXqVYWUGq3s7Wq8O13FA%2F4b00e85960ac9a8e8fada65485e7ac8c%2Fswimlanes-053b18bb5dcec8a714f9c9c8f9ae5ae7.png&w=3840&q=75&dpl=dpl_E2GZsUUM4EyvuYCes3krYpYUWFdo)
A common symptom of the issue described above can be an increase in errors reported by your users after a production deployment is created. The stale HTML is returned by the 3rd party CDN but other assets were purged from it, returning a 404. For that reason, we recommend users to either configure the 3rd party CDN with a very short TTL in the cache or disable it completely.
For more information, see Can I use a proxy on top of my Vercel Deployment?