Editing Contour Ingress Controller (section)

== External Services ==
The power of the Ingress is that it can serve as a reverse proxy, allowing one entry point to be directed wherever is needed to serve the request based on the hostname being accessed ... but if the complete suite of services includes capabilities outside of the kubernetes cluster, special actions must be taken to include them in the cluster reverse proxy.  The key to this capability is that Contour establishes routes to a kubernetes Service -- it doesn't care what the service is or how it is defined.  That abstraction simplifies the problem to simply creating a Service that references the external service.

Kubernetes includes a special Service type called '[https://kubernetes.io/docs/concepts/services-networking/service/#externalname ExternalName]' that effectively creates a CNAME in the cluster internal DNS that points to a FQDN provided in the Service specification:

<pre>apiVersion: v1
kind: Service
metadata:
  name: my-service
  namespace: prod
spec:
  type: ExternalName
  externalName: my.database.example.com</pre>

The port number of the external service is specified in the Ingress (or HTTPProxy) definition, and the connection is just redirected to the external service.  If encrypted communications is needed, the HTTPProxy can be used as described above.