In the context of software deployment, what does canary testing refer to?

Canary testing refers to the practice of deploying software changes to a small subset of users or servers prior to a wider rollout. The approach allows development teams to monitor and evaluate the new changes in a controlled setting before making them available to the larger population.

In the context of your response, the option that refers to sending changes to a single server and then scaling up accurately encapsulates this methodology. By first deploying to a single instance, teams can observe any issues or performance impacts in a real-world scenario while minimizing risk. If the initial deployment performs satisfactorily, the changes can then be gradually scaled up to a larger number of servers or users. This incremental approach helps identify bugs, performance issues, or negative impacts before wider release, ensuring a more stable and reliable product.

The other choices do not reflect the principles of canary testing accurately. Deploying changes without monitoring disregards the crucial observation phase central to canary testing. Releasing features to all servers simultaneously would not allow for targeted observation of potential issues. Finally, testing a new feature globally contradicts the essence of canary testing, which seeks to limit exposure initially to ensure a smooth transition for all users.