A network maintenance error separated an Azure West data center from the internet for hours

Several Microsoft Azure services hosted in its West US region went down for hours Thursday after a routine networking maintenance procedure inadvertently wound up isolating the region from the rest of the internet.

According to a "preliminary post incident review" posted late Thursday, Microsoft engineers were preparing to conduct maintenance on some networking devices Thursday morning. Standard operating procedure during such events involves re-routing network traffic away from the devices that need a tune-up by making sure requests for that network path have another place to go.