What technique is used to send changes to a percentage of servers and observe their behavior?

Canary testing is a technique utilized to introduce changes to a small percentage of servers in a controlled manner, enabling developers and operations teams to observe the behavior of the system before a full rollout. The term comes from the practice of sending a canary bird into coal mines; if the bird showed signs of distress, it indicated potential danger to the miners. Similarly, in canary testing, the "canary" servers help identify issues or unexpected behaviors in a software release, allowing teams to validate performance, functionality, and stability with minimal risk.

By deploying the new changes to a subset of servers, teams can monitor performance metrics, user interactions, and any potential errors or failures, making it easier to roll back changes if necessary or address any issues before a wider deployment. This approach essentially allows for real-world testing without subjecting all users to potential risks simultaneously, leading to increased confidence in software updates.