Metallb --lb-class cmd arg to support multiple LoadBalancer implementations

[Seal1998]

What type of PR is this?

/kind feature

What this PR does / why we need it:
In this PR, I tried using the new Metallb feature (effective from version 0.13.2), which is the ability to specify the --lb-class command line argument. This argument instructs MetalLB to listen exclusively for the loadBalancerClass defined in the .spec.loadBalancerClass of the LoadBalancer manifest.

In my scenario, this enhancement is very beneficial as I'm operating a cluster with multiple controllers that have the capability to monitor and manage the LoadBalancer service. Among these controllers are the cloud controller provided by my cloud provider and MetalLB respectively.

With this little change, I have configured MetalLB to strictly monitor a specific type of LoadBalancer, while delegating the management of all other LoadBalancer entities to the cloud controller.
Which issue(s) this PR fixes:

Not related to any particular issue

Special notes for your reviewer:
Thank you for your hard work! Version 2.23.0 is functioning smoothly. I'd really like to be able to specify loadBalancerClass in future releases
Does this PR introduce a user-facing change?:

Metallb --lb-class cmd arg to support multiple LoadBalancer implementations 

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: Seal1998 (688cce8, 7a1e078)

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[yankay]

/ok-to-test

[yankay]

Thanks @Seal1998

Is is better to define the loadbalancer_class at the https://github.com/kubernetes-sigs/kubespray/blob/v2.23.0/roles/kubernetes-apps/metallb/defaults/main.yml#L4 instead of the metallb_config .

The same as the metallb_port :-)

[Seal1998]

Hey @yankay, thanks for review! I have changed the condition and role defaults accordingly. Unfortunately, to my understanding, we cannot have the --lb-class flag defined by default, similar to --port. This is because it would instruct MetalLB to listen for a specific class of LoadBalancer. However, Kubernetes does not have any "default" class to listen for, as per its documentation. The loadBalancerClass is undefined by default on all LoadBalancer services. (https://kubernetes.io/docs/concepts/services-networking/service/#load-balancer-class)

By default, .spec.loadBalancerClass is not set and a LoadBalancer type of Service uses the cloud provider's default load balancer implementation if the cluster is configured with a cloud provider using the --cloud-provider component flag.

In my opinion, we should keep --lb-class undefined until the user specifically sets the metallb_loadbalancer_class variable to something meaningful. In this way, MetalLB will act as the 'default' LoadBalancer implementation until we specifically set --lb-class

Official metallb helmchart also uses this approach

{{- if .Values.loadBalancerClass }}
        - --lb-class={{ .Values.loadBalancerClass }}
{{- end }}

Please review

[yankay]

Thanks @ Seal1998 for the PR very much
/approve

[MrFreezeex]

Thanks for your contribution! :D
/lgtm

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: MrFreezeex, Seal1998, yankay

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