Rolling deployment is a technique that's used to gradually replace the current application with the newer version of it.

This kind of deployment technique allows you to have no downtime during the update, but also requires you to have the old and the new versions of the application running at the same time. This is only possible with data model compatibility.

Here are three diagrams depicting the beginning, the process, and the final stage of the deployment. At first, one instance of the new version of the application is deployed:

Once the new version of the application is ready to be used, which means that readiness and health checks are passed successfully, one instance of the old version is scheduled to be destroyed:

In the final stage, once the last expected instance of the new version of the application is ready to use, the last instance of the old version is destroyed, and only the new version is available: