Provide info for using Docker Hub as a container registry

[mckeeh3]

Short description

Add some info about using Docker Hub in the

Details

In section 7.1. Build Docker image, add some guidance for using Docker Hub vs AWS Container Registry.

On page https://developer.lightbend.com/docs/akka-platform-guide/microservices-tutorial/grpc-service.html#_build_docker_image

[patriknw]

We prefer the ECR because most real apps till be private and then you don't have to be concerned with authentication from inside EKS.

That said, we could have a how-to or some note about Docker Hub. The way I have used it is with:

mvn -DskipTests -Ddocker.username=patriknw -Ddocker.registry=docker.io/patriknw -Ddocker.password=$DOCKER_PWD clean package docker:push

There are other (better) authentication methods described in http://dmp.fabric8.io/#authentication

[mckeeh3]

Agree that for real projects ECR is better. However, many developers using the guide will just be taking a look. I know from my past experience the use of container repos has been a major hassle, in some cases resulting in significant frustration and lost hours trying to get it to work. This is one area where developers that are new to K8 and repos will run into trouble.