Unable to "easily" enable docker registries

[zadigus]

As it currently is, the nexus manifest installs a nexus instance on Jelastic that is pretty difficult to work with, especially with docker. In order to be able to have a useable docker registry, I had to modify your installation as follows:

1. add an nginx-dockerized node (bl node group)
2. replace automatic ssl on the environment with lets encrypt on the load balancer
3. add ssl nginx configurations for the ports the various docker registries will listen to
4. configure my docker registries with http connectors
5. add the relevant firewall rules to both the bl and cp node groups

Those modifications of your installation may be too much, I don't know. At least, that's working. For example, if I install this fork of your repository, then, with the right docker repository configuration, done like this, then it works fine, i.e. I can run a regular docker login against the deployed jelastic environment.

I think it would be valuable that someone writes an add-on to enable docker registries. I don't know if there is a way to make docker registries on nexus work with the jelastic built-in ssl (ssl: true in the manifest). It'd be a pain if that wasn't the case, because that would mean that, in order for docker registries to work, one would need to attach an IP address and install lets encrypt. Whatever the solution is to make it work, however, I am pretty sure it is doable through an add-on. What do you think?