Test ExternalName Service across Namespaces

We will create two namespaces, mesh, which is where the service mesh resides, and the blue namespace where our apps reside.

We will create a service in the mesh namespace called mesh, and a corresponding service of type ExternalName in the blue namespace called mesh-external, representing the mesh service in the mesh namespace.

Setup namespaces

kubectl create ns mesh 
kubectl create ns blue

Create the Mesh Pod/Service in the Mesh Namespace

kubectl run mesh --image=nginx:alpine --port=80 -n mesh 
kubectl expose pod/mesh -n mesh --type=LoadBalancer # important because the Service itself needs an IP

Create the ExternalName Service in the Blue Namespace

kubectl apply -f -<<EOF
kind: Service
apiVersion: v1
metadata:
  name: mesh-external
  namespace: blue
spec:
  type: ExternalName
  ports:
  - name: http
    port: 80
    protocol: TCP
    targetPort: 80
  externalName: mesh.mesh.svc.cluster.local
EOF

Create the curler pod

kubectl run curler --image=nginx:alpine -n blue

Curl against the externalName service

kubectl exec -it curler -n blue -- curl mesh-external

output

<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

Wait & Create Route

# Wait for IP to be present
until [ -n "$(kubectl get svc/mesh -n mesh -o jsonpath='{.status.loadBalancer.ingress[0].ip}')" ]; do
    sleep 7
done

kubectl apply -f -<<EOF
apiVersion: route.openshift.io/v1
kind: Route
metadata:
  name: mesh-external
  namespace: blue
spec:
  host: $(kubectl get svc mesh -n mesh -ojsonpath='{.status.loadBalancer.ingress[0].ip}')
  port:
    targetPort: http
  to:
    kind: Service
    name: mesh-external
EOF

Curl against OpenShift Route

curl $(kubectl get route mesh-external -n blue -ojsonpath='{.spec.host}')

output

<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

Clean Up

kubectl delete po,svc mesh --force -n mesh --grace-period=0

kubectl delete svc mesh-external -n blue --force --grace-period=0
kubectl delete pod/curler -n blue --force --grace-period=0
kubectl delete route --all -n blue

kubectl delete ns blue
kubectl delete ns mesh

cmwylie19/ExternalName.md

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