Azure AD B2C – Authentication Failures and Error Notifications– Mitigated

Summary of Impact: Between 09:13 and 10:22 UTC on 16 Mar 2022, a subset of end users of customers using Azure Active Directory B2C may have experienced failures and error notifications when attempting to authenticate. Retry attempts were likely to succeed during this incident. This issue is now mitigated.Preliminary Root Cause: An increased latency within underlying storage infrastructure, upon which our service depends on, led to a backlog of requests not being processed efficiently. This increased latency was due to an increased load on the North Europe datacenters. Typically, our systems scale to handle increased loads, however we exposed a bug due to which resources were not getting freed up as expected. This led to an exhaustion of processing resources in these datacenters.We detected the failures in less than 15 mins and by the 30-minute mark we had observed improvements. While we started drafting our initial communications to customers, we started observing a recovery for customers. As a result, the incident mitigated before we could send communications during the impact window.Mitigation: We performed a failover which mitigated this issue.Next Steps: We will continue to investigate to establish the full root cause and prevent future occurrences. You can stay informed about Azure service issues, maintenance events, or advisories by creating custom service health alerts (https://aka.ms/ash-videos for video tutorials and https://aka.ms/ash-alerts for how-to documentation) and you will be notified via your preferred communication channel(s).