k8s ExternalName endpoint not found - but working

Question

I deployed a simple test ingress and an externalName service using kustomize. The deployment works and I get the expected results, but when describing the test-ingress it shows the error: <error: endpoints "test-external-service" not found>. It seems like a k8s bug. It shows this error, but everything is working fine.

Here is my deployment:

kustomization.yaml:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
namespace: platform
resources:
  - test-ingress.yaml
  - test-service.yaml
generatorOptions:
  disableNameSuffixHash: true

test-service.yaml:

apiVersion: v1
kind: Service
metadata:
  name: test-external-service
  namespace: platform
spec:
  type: ExternalName
  externalName: "some-working-external-elasticsearch-service"

test-ingress.yaml:

apiVersion: networking.k8s.io/v1beta1
kind: Ingress
metadata:
  name: test-ingress
  annotations:
    kubernetes.io/ingress.class: nginx-external
    nginx.ingress.kubernetes.io/configuration-snippet: |
      proxy_cache_bypass $http_upgrade;
spec:
  rules:
    - host: testapi.mydomain.com
      http:
        paths:
          - path: /
            backend:
              serviceName: test-external-service
              servicePort: 9200

Here, I connected the external service to a working elasticsearch server. When browsing to testapi.mydomain.com ("mydomain" was replaced with our real domain of course), I'm getting the well known expected elasticsearch results:

{
  "name" : "73b40a031651",
  "cluster_name" : "docker-cluster",
  "cluster_uuid" : "Xck-u_EFQ0uDHJ1MAho4mQ",
  "version" : {
    "number" : "7.10.1",
    "build_flavor" : "oss",
    "build_type" : "docker",
    "build_hash" : "1c34507e66d7db1211f66f3513706fdf548736aa",
    "build_date" : "2020-12-05T01:00:33.671820Z",
    "build_snapshot" : false,
    "lucene_version" : "8.7.0",
    "minimum_wire_compatibility_version" : "6.8.0",
    "minimum_index_compatibility_version" : "6.0.0-beta1"
  },
  "tagline" : "You Know, for Search"
}

So everything is working. But when describing the test-ingress, there is the following error:

test-external-service:9200 (<error: endpoints "test-external-service" not found>)

What is this error? Why am I getting it even though everything is working properly? What am I missing here?

Answer 1

This is how the kubectl describe ingress command works.
The kubectl describe ingress command calls the describeIngressV1beta1 function, which calls the describeBackendV1beta1 function to describe the backend.

As can be found in the source code, the describeBackendV1beta1 function looks up the endpoints associated with the backend services, if it doesn't find appropriate endpoints, it generate an error message (as in your example):

func (i *IngressDescriber) describeBackendV1beta1(ns string, backend *networkingv1beta1.IngressBackend) string {
    endpoints, err := i.client.CoreV1().Endpoints(ns).Get(context.TODO(), backend.ServiceName, metav1.GetOptions{})
    if err != nil {
        return fmt.Sprintf("<error: %v>", err)
    }
...

In the Integrating External Services documentation, you can find that ExternalName services do not have any defined endpoints:

ExternalName services do not have selectors, or any defined ports or endpoints, therefore, you can use an ExternalName service to direct traffic to an external service.