Microsoft Standard CDN, cache expires too soon causing frequent cache misses

Question

I'm using the standard microsoft CDN in front of an Azure Storage Static website.

The origin doesn't respond with any cache headers (not supported by Static Website), but I have configured in my endpoint rules engine with the following.

"Then 'Cache Expiration', Override, 90 days", which at least appears to set the cache-control header in the CDN response.

From the docs I've read, this 'Cache Expiration' setting should also inform the CDN POP to cache for 90 days. However, while testing I have noticed that in visits after 1 day, about 30% of requests are served as 'TCP_REMOTE_HIT' and another 30% as 'TCP_MISS'.

Is the setting for Cache Expiration correct, to specify the cache expiration at the POPs? Or is there some other reason for such quick evacuation of the cache at the POPs.

Answer 1

@Rem Thank you for your patience while we were looking into this issue.

1. Microsoft does code rollouts once a week in production and all services restart fresh i.e., Entire cache is gone.
2. If the item is not accessed frequently, the item gets evicted out of cache by more popular items. This behavior is expected.

Hope this helps. If you have any further questions/concerns, please do let us know. Thank you!