The canonical way to deploy Rails app to ECR with buildpacks

We are changing hosting platforms and due to time restrictions, we want to continue to build our Rails app with buildpacks rather than going fully to a Dockerfile.

We are aren’t looking to just push the code to AWS and build the image on CodeBuild.

What we are doing is installed pack CLI on the Circle side and trying to pack build the application with buildpacks and then docker push the image to ECR.

Is this a normal thing to do?

Some on our team I think are concerned about doing the build on the Circle CI because it would mean putting production env vars on Circle but I don’t think that’s any less safe than storing them on AWS. As far as I know the containers and VMs used for our pipelines are destroyed after jobs.