Microsoft Azure outage, 18 July 2024

Azure Central US storage allow-list outage (18 July 2024). The disruption lasted about 24 hours 20 minutes, according to Microsoft Azure’s own timeline.

What happened. A routine update to the storage ‘allow list’ of VM host addresses was generated while some source file servers were unreachable, and the workflow didn’t notice the missing files. The incomplete list was pushed to all Storage scale units in the region without zone sequencing, so storage rejected disk I/O from many VM hosts.

What changes. Microsoft fixed allow-list generation to halt on incomplete data and now deploys it serialized by Availability Zone over 24 hours.

Questions

What caused the Microsoft Azure outage in July 2024?

A routine update to the storage ‘allow list’ of VM host addresses was generated while some source file servers were unreachable, and the workflow didn’t notice the missing files.

Which services were affected?

Azure Storage, Virtual Machines, SQL Database, Cosmos DB, App Service, Entra ID and many more; Microsoft 365, Dynamics 365.

Read how shared dependencies spread a failure in why one cloud outage can break unrelated apps, or browse the outage archive.