Strategies

• rolling deployment with replacement: replace instances and redirect user traffic in batches (one or more).
• blue-green deployment: deploy all new instances at once and redirect traffic immediately.
• canary deployment: deploy a single instance, redirect to it and pause deployment to compare metrics between the new version ("canary") and any old version ("control"). If newer code performs as expected compared to older code resume deployment using any strategy, otherwise abort. A good approach is to hide new features behind toggles and first compare the deployment without them to check for any differences.

Picking a strategy depends on how important it is that all instances run the same code at once. If it's necessary use blue-green, if your code needs and allows gradual testing of the new features use canary, otherwise rolling will suffice.

Artifact promotion

When deploying an artifact, a common approach is to gradually introduce it into the environments. In such process each step is called an artifact promotion:

• dev environment, where tests are run.
• stage environment, where artifact is deployed to the testing infrastructure.
• prod environment, where artifact becomes available to users.