Kubernetes StatefulSets: External DNS

Question

Kubernetes StatefulSets create internal DNS entries with stable network IDs. The docs describe this here:

Each Pod in a StatefulSet derives its hostname from the name of the StatefulSet and the ordinal of the Pod. The pattern for the constructed hostname is $(statefulset name)-$(ordinal). The example above will create three Pods named web-0,web-1,web-2. A StatefulSet can use a Headless Service to control the domain of its Pods. The domain managed by this Service takes the form: $(service name).$(namespace).svc.cluster.local, where “cluster.local” is the cluster domain. As each Pod is created, it gets a matching DNS subdomain, taking the form: $(podname).$(governing service domain), where the governing service is defined by the serviceName field on the StatefulSet.

I am experimenting with headless services, and this works great for communication between individual services i.e web-0.web.default.svc.cluster.local can connect and communicate with web-1.web.default.svc.cluster.local just fine.

Is there any way that I can configure this to work outside of the cluster network as well, where "cluster.local" is replaced with something like "clustera.com"?

I would like to give another kubernetes cluster, lets call it clusterb.com, access to the individual services of the original cluster (clustera.com); I'm hoping it would look something like clusterb simply hitting endpoints like web-1.web.default.svc.clustera.com and web-0.web.default.svc.clustera.com.

Is this possible? I would like access to the individual services, not a load balanced endpoint.

Answer 1

I would suggest you to test the following solutions and check if they can help you to achieve your goal in your particular scenario:

• The first one is for sure the easiest and I believe that you didn't implemented it for some reason and you did not reported in the question why.

  I am talking about Headless services Without selectors CNAME records for ExternalName-type services.

  ExternalName: Maps the service to the contents of the externalName field (e.g. foo.bar.example.com), by returning a CNAME record with its value. No proxying of any kind is set up. This requires version 1.7 or higher of kube-dns

  Therefore if you need to point a service of an other cluster you will need to register a domain name pointing to the relative IP of clusterb.

• The second solution that I have never tested, but I believe it can apply to your case is to make use of a Federated Cluster whose reason why to use it is accordinding to the documentation:

  Cross cluster discovery: Federation provides the ability to auto-configure DNS servers and load balancers with backends from all clusters. For example, you can ensure that a global VIP or DNS record can be used to access backends from multiple clusters.