Use kubernetes-client and Kubernetes Service Discovery Enhancements

[ogmaresca]

A re-do of #231 that uses https://github.com/kubernetes-client/csharp

• Add support for service annotations to override the defaults on a per-service basis:

• HealthChecksPath: Override the health check path.
• HealthChecksPort: Override the health check port if it isn't using the first defined port.
• HealthChecksScheme: Override the URI scheme (for HTTPS support).

• Add support for limiting the service discovery to specified namespaces.
• Intelligent kubernetes client config loading. If the pre-existing Host and Token config fields are not defined, then it'll use the in-cluster config if running in a pod and use the ~/.kube/config file otherwise.
• Add IPv6 support for ClusterIP addresses.
• Add ExternalName service type support
• Add an example for role based access in the README.

[CarlosLanderas]

@ggmaresca this is great!. No further need to add the kubernetes client. Im gonna review this and we merge this and the k8s operator.

[CarlosLanderas]

@ggmaresca I've been testing the PR and looks great :). Can you address the review points?

Thanks!

[ogmaresca]

@CarlosLanderas I've split out services.AddKubernetesServiceDiscovery();.

[CarlosLanderas]

Oh, I've spelled it wrong, it should be
AddKubernetesDiscoveryService to match the appsettings. My fault. Could you change it and add the services null check that produces crashes when no services are found?

With that this should be reeeeeady

[ogmaresca]

Did the method rename. What do you mean by the service null check?

[sungam3r]

Perhaps check this IServiceCollection services parameter on null.

[CarlosLanderas]

What is more correct? visible or reachable?

[CarlosLanderas]

This crashed while testing the branch as no services were found. services NullReference Exception. This should be checked.

[CarlosLanderas]

Did the method rename. What do you mean by the service null check?

services in services.Items might be null and crash. I've suffered it while testing the branch. It's not your fault, it was already like that but if we fix it we merge this without further thoughts ;)

AspNetCore.Diagnostics.HealthChecks/src/HealthChecks.UI/Core/Discovery/K8S/KubernetesDiscoveryHostedService.cs

Line 71 in 5d19839

foreach (var item in services.Items)

[CarlosLanderas]

@ggmaresca thanks for the contribution!. It is finally merged ;)