https://www.bleepingcomputer.com/news/microsoft/massive-microsoft-365-outage-caused-by-faulty-ecs-deployment/

In a preliminary post-incident report, Microsoft has revealed that this week's 5-hour-long Microsoft 365 worldwide outage was triggered by a faulty Enterprise Configuration Service (ECS) deployment that led to cascading failures and availability impact across multiple regions.

ECS is an internal central configuration repository designed to enable Microsoft services to make wide-scope dynamic changes across multiple services and features, as well as targeted ones such as specific configurations per tenant or user.