Kubernetes ExternalName services and Kubernetes services with Endpoints let you create a local DNS alias to an external service. This DNS alias has the same form as the DNS entries for local services, namely <service name>.<namespace name>.svc.cluster.local. DNS aliases provide location transparency for your workloads: the workloads can call local and external services in the same way.
https://istio.io/latest/docs/tasks/traffic-management/egress/egress-kubernetes-services/
ExternalName
Services of type ExternalName map a Service to a DNS name, not to a typical selector such as my-service or cassandra. You specify these Services with the spec.externalName parameter.
This Service definition, for example, maps the my-service Service in the prod namespace to my.database.example.com:
apiVersion: v1
kind: Service
metadata:
name: my-service
namespace: prod
spec:
type: ExternalName
externalName: my.database.example.comhttps://kubernetes.io/docs/concepts/services-networking/service/#externalname