...The master branch will sometimes have changes that are still in the process of being released in AWS CodeBuild. When you provide information to CodeBuild about the build environment, you specify the identifier of a Docker image in a supported repository type. These include the CodeBuild Docker image repository, publicly available images in Docker Hub, and Amazon Elastic Container Registry (Amazon ECR) repositories that your AWS account has permission to access. We recommend that you use Docker images stored in the CodeBuild Docker image repository, because they are optimized for use with the service.