Explore Microsoft's safe deployment process (SDP)
Once a build has passed all required testing and review, it's ready to be introduced for production use. New builds are released through a "safe deployment process" (SDP), which is a gradual, staged roll out to increasingly large percentages of the service. Each stage is called a "ring," beginning with "Ring 0" and expanding outwards. Builds run in each ring for an appropriate number of high-load periods, such as workdays, to ensure stability before proceeding to the next ring. The exact definition, size, and composition of the rings varies by service and the requirements of each service. For Microsoft Online Services, the rings are defined as follows:
Ring 0 is comprised of the development team responsible for that service. This ring exposes the build to Microsoft employees most responsible for the affected service.
Ring 1 is comprised of all Microsoft employees. This ring exposes the build to more users for thorough testing prior to customer release.
Ring 2 is the first exposure of the build to users outside Microsoft. This ring is often called a SIP, or "Slice In Production." A SIP is typically a unit of capacity about an order of magnitude larger than Ring 1.
Ring 3-N, where N represents the final deployment ring, exposes the build to progressively larger percentages of the total service until the entire service has been updated. Because the build has already been exercised at scale in prior rings, the build progresses through these rings more quickly, waiting long enough to ensure stability before deploying the next unit of capacity.