Service externalName: IP?

General Discussions
1

Can I set IP instead of dns name?
Somethig like this

kind: Service
apiVersion: v1
metadata:
  name: external-grafana
  namespace: kube-system
spec:
  type: ExternalName
  externalName: 207.244.95.62
  ports:
  - port: 3000
2

You can indeed, here is an example I just tested:

apiVersion: v1
kind: Service
metadata:
  name: google-dns
spec:
  type: ExternalName
  externalName: 8.8.8.8
  ports:
    - port: 53
      protocol: UDP

listing services

$ kubectl get svc
NAME         TYPE           CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
google-dns   ExternalName   <none>       8.8.8.8       53/UDP    2m
kubernetes   ClusterIP      10.96.0.1    <none>        443/TCP   1d

nslookup from within a container

 # nslookup google-dns.default.svc.cluster.local

Name:      google-dns.default.svc.cluster.local
Address 1: 8.8.8.8 google-public-dns-a.google.com
3

Oddly I can’t get mine to work. I am using CoreDNS, do you know if that might affect it?
I can get it working if I create a Service with no selectors and manually create the Endpoints.

4

I tested it with an instance of CoreDNS and it did not seem to impact it, but ExternalName should not use any selectors or additional endpoints referenced, its meant to point to an external entity whether it be a dns name or ip address – pretty much setting it manually in the service definition.

5

Below is my exact YAML file for creating the externalName Service, can you see anything wrong with it? Any ideas on what I can check next? Thanks by the way!

apiVersion: v1
kind: Service
metadata:
  name: kafka
spec:
  type: ExternalName
  externalName: 10.59.208.211
  ports:
    - name: kafka
      port: 9092
      protocol: TCP
    - name: zookeeper
      port: 2181
      protocol: TCP
6

At this point my guess is there might be something else afoot. I was able to create the service you posted both in minikube and another cluster (both running 1.10.x)

$ kubectl describe service kafka
apiVersion: v1
kind: Service
metadata:
  creationTimestamp: 2018-05-23T17:54:20Z
  name: kafka
  namespace: default
  resourceVersion: "61858"
  selfLink: /api/v1/namespaces/default/services/kafka
  uid: 51b77866-5eb2-11e8-b3dc-0800279f676b
spec:
  externalName: 10.59.208.211
  ports:
  - name: kafka
    port: 9092
    protocol: TCP
    targetPort: 9092
  - name: zookeeper
    port: 2181
    protocol: TCP
    targetPort: 2181
  sessionAffinity: None
  type: ExternalName
status:
  loadBalancer: {}
8

I have just read this in K8 docs:

Note:

ExternalName accepts an IPv4 address string, but as a DNS name comprised of digits, not as an IP address. ExternalNames that resemble IPv4 addresses are not resolved by CoreDNS or ingress-nginx because ExternalName is intended to specify a canonical DNS name. To hardcode an IP address, consider headless services.

9

Not sure what your question is. Can you please elaborate?

In any case, think of service external name as a DNS cname. Does that help? If not, please share your question :slight_smile:

1 Like
10

For those who still comes to this thread, here’s a link with 3 scenarios to map external services:


In short, use a combination of Service and Endpoints.

I have successfully tested an externalName with an IP address on GKE but I prefer to use the correct way to do it.

Terraform documentation for Kubernetes provider on Endpoints: https://www.terraform.io/docs/providers/kubernetes/r/endpoints.html

11

The Kubernetes best practices: mapping external services post is redirecting to another one. The original can be read in archive.org.

Inline video is Mapping External Services - YouTube.

1 Like