Remove externalTrafficPolicy from template for service type ClusterIP

[birke-kb]

Add a condition to specify externalTrafficPolicy in the apisix-gateway service spec only for service types LoadBalancer and NodePort. Adding the field for service type ClusterIP leads to configuration errors in Kubernetes.

[eedeebee]

Hi apisix folks - thanks for making and maintaining this chart!

Is there anything else needed for this PR to get reviewed?

It addresses #755 and #780 which have been open for 2 years. I'm happy to help or add whatever it takes to get it in.

[martin-mat]

Confirming this is still needed on the current chart (apisix 2.17.0, APISIX 3.18.0). With service.type: ClusterIP, the install fails on Kubernetes 1.35:

Error: INSTALLATION FAILED: 1 error occurred:
	* Service "apisix-gateway" is invalid: spec.externalTrafficPolicy: Invalid value: "Cluster": may only be set for externally-accessible services

The template sets externalTrafficPolicy unconditionally, and the API server accepts it only on LoadBalancer and NodePort Services. This PR renders it for exactly those two types, so a ClusterIP gateway installs and the other types are unchanged. Fronting the gateway with an Ingress or a cloud load balancer is a common reason to want ClusterIP, as #755 and #780 describe.

The workaround in the meantime, for anyone landing here, is service.externalTrafficPolicy: null in the values.

Could a maintainer review this? It fixes #755, open since May 2024. Earlier attempts at the same fix (#792, #816) went stale without review.