Hi everyone,
Just recently we started having issues in our integration environment with publicly available well known files not being fetched properly by the Apple CDN. The CDN keeps returning an SWCERR00301 Timeout fault.
I noticed a very similar thread around the same time it went wrong with us as well: https://developer.apple.com/forums/thread/821908
However, the fault is ever so slightly different.
Note that for security reasons, the actual domain has been redacted and replaced by the generic "domain.com"
When calling the command
curl -i https://app-site-association.cdn-apple.com/a/v1/domain.com
The following is returned
HTTP/1.1 404 Not Found
Server: AppleHttpServer/2caa77a6bc2e755fca0e0f63e4d67e53390f9184
Date: Thu, 21 May 2026 10:44:08 GMT
Content-Type: text/plain; charset=utf-8
Content-Length: 10
Apple-Failure-Details: {"cause":"Connection timed out"}
Apple-Failure-Reason: SWCERR00301 Timeout
Apple-From: https://domain.com/.well-known/apple-app-site-association
Apple-Try-Direct: true
Cache-Control: max-age=3600,public
Vary: Accept-Encoding
X-B3-TraceId: eb38e1901a83ad9b
Strict-Transport-Security: max-age=31536000
Expires: Thu, 21 May 2026 10:44:18 GMT
Age: 712
Via: http/1.1 defra2-vp-vst-004.ts.apple.com (acdn/302.16436), https/1.1 defra2-vp-vfe-007.ts.apple.com (acdn/302.16436), https/1.1 nlams2-edge-lx-007.ts.apple.com (acdn/302.16436), https/1.1 nlams2-edge-bx-021.ts.apple.com (acdn/302.16436)
X-Cache: hit-fresh, hit-stale, hit-stale, hit-stale
CDNUUID: 859e620c-7e2c-438c-a43d-68b6344e890c-1593129103
Connection: keep-alive
Not Found
Where other issues on the forum specifically target "waiting on headers", it does not in our case.
We checked our internal infrastructure, we clearly see incoming requests from the ASAA-bot requesting the well known file. These requests hit our backends as they should and return a 200 OK. All within a couple of milliseconds. Again - nothing changed here.
After this validation, I read the Tech notes: TN3155: Debugging universal links | Apple Developer Documentation but it does not provide anything we did not already check. Besides on our side, hosting wise and content-wise, nothing changed. This is not new material.
I ultimately enabled developer mode on my test device, pushed the Integration app version causing the issues.
- When keeping the entitlements asis, the apple CDN is called from the iOS device (verified through ProxyMan) but the redirects do not work (as the CDN contains 404 Not Found)
- When changing the entitlements, and adding "?mode=developer", the CDN is of course skipped and our backend is called directly (as verified through ProxyMan). Now the redirects work as intended, the universal links were fetched properly.
(the embedded universal link tester on the iOS device in settings - Developer still did not validate the universal link correctly though. But this seems an issue in the tool. The working production universal link also does not validate while it definitely works)
To make sure our backend is not too 'slow' (internal logging shows requests are handled within 100 ms), I checked against UAT. Same processing times, there no issues with CDN.
We conducted a very thorough investigation on our side and I do not see any reason as to why the CDN should be throwing timeout exceptions.
As we cannot flush the CDN cache and do not see issues on our side, there is no way for us to validate why this is going wrong.
Does anyone have any clues on what else I can do?
Thanks
