Link: Configuring your release pipelines for safe deployments

“Also, it is recommended to not deploy to all production environments in one go, exposing all the customers to the changes. A gradual rollout that exposes the changes to customers over a period, thereby implicitly validating the changes in production with a smaller set of customers at a time… As an example, for an application is deployed in 12 regions with US regions (4) having a high load, European regions (4) having a medium load and Asian regions (4) having a relatively lighter load, following would be the order of rollout.”
Original source: Configuring your release pipelines for safe deployments