Here’s a root analysis provided by Microsoft:
The Microsoft Azure Team has investigated the issue reported and we have identified it was due to a dependency that the Azure Web App service takes on Azure Storage.
In this specific scenario, a storage cluster experienced a larger than normal network traffic volume. Engineers initially triaged this to be due to a possible increased traffic load. Thus, the first mitigation performed was to modify a configuration setting to allow for an additional volume increase. However, this change alleviated some of the pressure but did not solve the underlying problem. Additional troubleshooting determined that the majority of the remaining impact was due to a lock contention in the storage volume, primarily due to the cluster being overloaded from the initial traffic increase.
After mitigating the issue, engineers were able to solve the issue of the increased traffic volume by putting in place mechanisms that would distribute the volume for the specific scenario that resulted in this incident. Additionally, future improvements are planned to address the interaction between storage cluster dependencies and network volume fluctuations.
We apologize for any inconvenience.
The Microsoft Azure Team