[loki-distributed] Add 'grpclb' port to query-frontend service

[Tristan971]

Fixes #801, albeit not necessarily the right way about it...

From a maintenance perspective it's fragile to just add a duplicate port like that, and from a BC perspective we can't necessarily just rename the old one either.

There's definitely something that needs to happen, but I'm not sure this is it, even though it does the trick.

[torstenwalter]

@Tristan971 please update the docs.
For me this looks good. I was just thinking if we should also update the targetPort to make it easier to drop the existing (old) grpc port when making a breaking change e.g. a 1.0.0 release.

@unguiculus what do you think about the PR?

[Tristan971]

For the target port name change, I would certainly not mind, but was similarly thinking "technically breaking change" if someone made their own service for some reason, so refrained from touching it

I guess we could introduce an extra named port on the deployment rather than renaming the existing?

Will get docs fixed in a second

[torstenwalter]

Makes sense so we could leave the targetPort as is.

[Tristan971]

Had never tried, and can't find any doc to explain it, but it would seem that you cannot have 2 portMappings on a single container that have the same number/protocol but different names...

At least on the k8s version I'm on (1.21.5) it just discards one of them.

I'm afraid we'll need to stick to it being 'grpc' at the pod level until 1.0 hits

[Tristan971]

Any updates on this?

[Whyeasy]

LGTM!