Docker is used to package up our applications with all of the parts they need, such as libraries and other dependencies, and enable us to ship it all out as one package. Our repositories hosted in AWS CodeCommit are automatically built by AWS CodeBuild on changes (resulting from Pull Requests being approved) and these are stored in the the EC2 Container Registry (ECR) before being approved for deployment to the Amazon EC2 Container Service in a zero-downtime, staged upgrade. We also provide development instances of our Apps, which are also hosted in Docker containers.