We are running a setup consisting:
- S3 web app in UK South
- S2 failover in UK West
- 200DTU Elastic Pool with around 25 databases
- Redis server
Several times this week, we have had periods where Redis has stopped hitting and missing data, and no additional items are being added to the cache. In effect the caching completely ceases being available.
Flushing the cache does not make any difference to the issue - nothing is added, nothing is hit or even missed.
The only way to re-enable is to restart the web app itself. After which everything is back to normal.
I have attached an example showing gaps between around 11am-1pm where cache suddenly stopped functioning, and the effect of a restart can be seen.
Our developers are looking into potential causes in our codebase, but I wonder if anyone has any ideas on how to diagnose or solve this issue.