Rethink building SNI for multizone MeshService

[jakubdyszkiewicz]

Description

The current way is a bit hacky
#10451 (comment)
While it works, we should consider something more robust.

Options that come to my mind:

1. More labels
2. Put SNI in MeshService and sync it cross zone. This is nice but how to handle splits?

xref #10435

[jakubdyszkiewicz]

xref #10918

[lahabana]

@jakubdyszkiewicz does this cover the implem of MADR-59?

[jakubdyszkiewicz]

yes, it's basically implem of https://github.com/kumahq/kuma/blob/master/docs/madr/decisions/059-sni-in-the-resource.md

[lahabana]

Put SNI in MeshService and sync it cross zone. This is nice but how to handle splits?

Do we agree that we decided to not do splits?

[lahabana]

Also we agree that the format is agreed on and this change would be just to remove the zone CP to "make up" the format for remote access to services?

In other words this is an improvement but there wouldn't be a breaking change in implementing this (just if the SNI is in the MeshService object use this instead)

[jakubdyszkiewicz]

Do we agree that we decided to not do splits?

Yes, we do not do splits anymore

[lahabana]

The code for computing the SNI is in:

kuma/pkg/core/resources/apis/meshservice/api/v1alpha1/helpers.go

Lines 74 to 95 in 4d8c12d

	// todo(jakubdyszkiewicz) strongly consider putting this in MeshService object to avoid problems with computation
	func (t *MeshServiceResource) SNIName(systemNamespace string) string {
	displayName := t.GetMeta().GetLabels()[mesh_proto.DisplayName]
	namespace := t.GetMeta().GetLabels()[mesh_proto.KubeNamespaceTag]
	origin := t.GetMeta().GetLabels()[mesh_proto.ResourceOriginLabel]
	if origin == string(mesh_proto.GlobalResourceOrigin) {
	// we need to use original name and namespace for services that were synced from another cluster
	sniName := displayName
	if namespace != "" {
	// when we sync resources from universal to kube, when we retrieve it has KubeNamespaceTag as label value
	if systemNamespace == "" || systemNamespace != namespace {
	sniName += "." + namespace
	}
	}
	return sniName
	}
	if systemNamespace == "" && origin == string(mesh_proto.ZoneResourceOrigin) && namespace != "" {
	// when namespace label was added to Universal MeshService to have a copy of Kubernets MeshService
	return t.GetMeta().GetName() + "." + namespace
	}
	return t.GetMeta().GetName()
	}