Support of allowEmptyServices in TraefikService

[jeromeguiard]

What does this PR do?

This PR fix issue #9423 related to flag not taken into account for traefik service

Motivation

It is a bug in the configBuilder object that doesn't represent expected code behavior

Fixes #9423

More

• Added/updated tests
• Added/updated documentation

[ldez]

Hello,

can you explain the draft state of this PR?

Because if it's a draft we will not review it.

[jeromeguiard]

Hello,

The draft status was because I wanted to make sure about the tests. I added one instead of changing an existing one.

It is done now.

Thanks

[rtribotte]

Hello @jeromeguiard,

We thought about the changes and about the use case, and here are our takes:

• We do agree that the propagation of the allowEmptyServices option all along TraefikServices is missing. So we are moving the PR to the review state.

• Regarding Canary or Blue/Green deployment scenarios, we think that propagating the allowEmptyServices option would help if weights of the WRR are correctly managed. Indeed, propagating the allowEmptyServices makes it possible to build a WRR with some services that have servers and some others that don't. This would make a fraction of requests (depending on the weight) end up with a 503 status code.

• Nonetheless, because the allowEmptyServices option is a provider option, it would impact all services discovered by the IngressRouteCRD provider. Having to leverage it to support properly Blue/Green deployments may not fit in every situation. Hence, we may lack an alternative, for instance, ignoring zero-weight WRR services (that will, anyway, never handle the traffic).

[rtribotte]

Thanks 👍

[kevinpollet]

Thanks 👍