Enable publish-service for ClusterIP type service. fixes #4461

[rtnpro]

What this PR does / why we need it:

This pull request enables publishing the ClusterIP for nginx-ingress-controller service when the service's type is ClusterIP.

Which issue this PR fixes
fixes #4461

[k8s-ci-robot]

Welcome @rtnpro!

It looks like this is your first PR to kubernetes/ingress-nginx 🎉. Please refer to our pull request process documentation to help your PR have a smooth ride to approval.

You will be prompted by a bot to use commands during the review process. Do not be afraid to follow the prompts! It is okay to experiment. Here is the bot commands documentation.

You can also check if kubernetes/ingress-nginx has its own contribution guidelines.

You may want to refer to our testing guide if you run into trouble with your tests not passing.

If you are having difficulty getting your pull request seen, please follow the recommended escalation practices. Also, for tips and tricks in the contribution process you may want to read the Kubernetes contributor cheat sheet. We want to make sure your contribution gets all the attention it needs!

Thank you, and welcome to Kubernetes. 😃

[k8s-ci-robot]

Hi @rtnpro. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: rtnpro
To complete the pull request process, please assign aledbf
You can assign the PR to them by writing /assign @aledbf in a comment when ready.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[rtnpro]

I have tested this PR in my Kubernetes cluster, and it's able to publish the ClusterIP of the nginx-ingress-controller ClusterIP type service to the associated ingress objects.

If this change is desirable, then I can go ahead with adding tests for this fix.

[aledbf]

@rtnpro I am sorry but ClusterIP addresses are not routable outside the cluster. That's the reason why
this is not supported. What are you trying to do exactly?

[rtnpro]

On Sun, Aug 18, 2019 at 9:41 AM Manuel Alejandro de Brito Fontes ***@***.***> wrote: @rtnpro I am sorry but ClusterIP addresses are not routable outside the cluster. That's the reason why this is not supported. What are you trying to do exactly?

@aledbf I have setup OpenVPN inside my Kubernetes cluster using https://github.com/helm/charts/tree/master/stable/openvpn and have exposed the OpenVPN service via `NodePort` type service. So, once I connect to this VPN, I have access to all cluster IPs in my cluster. All that was remaining is to create DNS entries for cluster IPs for certain services. This can be achieved by `external-dns` only if the ingress gets `endpoints` published to them. This is a valid use case in cloud providers like Digitalocean where they do not offer private load balancers. So, in this way, I can create a secure internal network for certain internal applications in my kubernetes cluster along with DNS resolutions for the internal hostnames. I hope that this makes sense.

[rtnpro]

@aledbf ping!

[rtnpro]

@aledbf Hey, I have written a blog post explaining why we need this feature: https://rtnpro.com/enabling-publish-service-for-clusterip-nginx-ingress-controller-service/

Let me know what you think about it.