Canary Testing, also known as canary deployments, incremental, staged, or phased rollouts, is a powerful approach in software development that aims to reduce risk and validate new software releases. The idea behind canary testing is to release the software to a small percentage of users first, allowing you to deliver it in stages to specific groups. This process serves as a safety net, allowing you to quickly detect and address any issues with the new software before it affects a broader audience. Canary testing has become a best practice in the world of DevOps and software development.

The Origin of Canary Testing

The term “Canary in the coal mine” has its origins in coal mining, where miners used to bring a caged canary bird into the mine. The canary, being more sensitive to toxic gases than humans, would show signs of distress or even die if the gas levels became dangerous. This served as an early warning system for the miners to evacuate the mine promptly. In the context of software development, canary testing acts as a preventive measure to ensure new software does not lead to catastrophic consequences but instead improves the overall user experience.

How to Do Canary Testing

Blue-Green Deployments

One way to conduct canary testing is through the use of blue-green deployments. This method involves splitting traffic at the server-level and gradually redirecting it from the older version of the application to the newer one, using a traffic router. This incremental approach helps you monitor the software’s behavior and performance in a controlled manner.

Feature Flags

Alternatively, canary testing can be done more granularly at the feature level using feature flags. These flags allow teams to separate code release from feature enablement, making it possible to turn features on and off remotely for specific groups or percentages of users. This level of control allows teams to limit the release to just 1% of users initially and closely monitor key metrics such as error rates and latency to ensure a smooth deployment.

Benefits of Canary Testing

Minimizing Risk and Validation

By releasing new code or features to a small subset of users first, canary testing allows teams to identify and resolve issues early on. This controlled release minimizes the potential impact of bugs or glitches, validating the functionality and performance of the software before rolling it out to a larger audience.

Testing in Production

Canary testing is particularly useful because development and staging environments may not fully replicate the production environment. By testing with a small percentage of production users, teams can uncover issues that may have been missed during development and staging.

Easy Rollback with Feature Flags

The use of feature flags in canary testing makes it easy to disable a new feature or code if issues are detected during the deployment process. This ability to quickly rollback helps prevent major downtimes, revenue loss, and negative customer experiences.

Canary Testing and Continuous Delivery

Canary testing is closely aligned with the principles of continuous delivery. In the world of software development, continuous delivery allows software to be released to production at any time. Canary testing fits seamlessly into this methodology, enabling teams to safely release new features and code changes at scale.

Companies like Facebook, renowned for their best-in-class continuous delivery systems, integrate deep monitoring and automated testing into their canary testing process. If a feature fails during the canary deployment, it will automatically roll back, ensuring a smooth user experience.