After service recovery, the Microsoft Azure team is providing more detail regarding the service disruption that occurred on May 2, 2019.

Here is that detail directly from Microsoft:

Network Connectivity - DNS Resolution

Summary of impact: Between 19:43 and 22:35 UTC on 02 May 2019, customers may have experienced intermittent connectivity issues with Azure and other Microsoft services (including M365, Dynamics, DevOps, etc). Most services were recovered by 21:30 UTC with the remaining recovered by 22:35 UTC.

Preliminary root cause: Engineers identified the underlying root cause as a nameserver delegation change affecting DNS resolution and resulting in downstream impact to Compute, Storage, App Service, AAD, and SQL Database services. During the migration of a legacy DNS system to Azure DNS, some domains for Microsoft services were incorrectly updated. No customer DNS records were impacted during this incident, and the availability of Azure DNS remained at 100% throughout the incident. The problem impacted only records for Microsoft services.

Mitigation: To mitigate, engineers corrected the nameserver delegation issue. Applications and services that accessed the incorrectly configured domains may have cached the incorrect information, leading to a longer restoration time until their cached information expired.

Next steps: Engineers will continue to investigate to establish the full root cause and prevent future occurrences. A detailed RCA will be provided within approximately 72 hours.