Hi there, I did it on DO with default k8s way
https://kubernetes.io/docs/tasks/configure-pod-container/pull-image-private-registry/

Has anyone had any success configuring Amazon ECR as a private registry?

Look at Helm charts (package management for Kubernetes solution sets).

An example of setting up a registry on K8s can be seen here in step 3: https://www.katacoda.com/javajon/courses/kubernetes-serverless/openfaas

A UI can be added to this using the above headless registry: https://medium.com/quiq-blog/docker-registry-ui-874c890d2c9b

You can also utilize registry vendors and their community editions that offer container registries as a plugin (container registries are just one type of registry) to their wide array of registry solutions.

https://github.com/helm/charts/tree/master/stable/sonatype-nexus
https://github.com/helm/charts/tree/master/stable/artifactory

Later, you may also want to use these solutions for hosting Helm charts, jars, npm dependencies, etc.

Also:

http://port.us.org/

A large HA enterprise option is Quay that can run privately on K8s. Has very nice account and staging features and also support Helm chart repositories.

Add a security scanner to the registry with Clair.