HealthChecks state

[lkurzyniec]

Idea

Currently, there is no way to retrieve the current health checks state directly.

To get the status/state, it is necessary to resolve the HealthCheckService from the DI container and call CheckHealthAsync().

If either IHealthCheckPublisher is registered, or a health check endpoint is configured (e.g., endpoints.MapHealthChecks("/healthz/ready", Predicate = healthCheck => healthCheck.Tags.Contains("ready"))) and integrated with a Kubernetes readiness probe, the current state is already available as one of the above "calculate" it by invoking HealthCheckService.CheckHealthAsync() on their own.

The proposed approach is to register as singleton a transfer object (ie HealthChecksState) and stores there a RefreshDate and the HealthReport.

That would make a way to easly get the health checks state as well as reduce number of calls to registered health check endpoints (as those are made by either IHealthCheckPublisher and/or readiness probe).

Motivation

1. Infrastructure Health Validation Before Job Processing
   A HostedService queries the database every 5 seconds to retrieve pending jobs. Before processing each batch, I would like to have an option to verify the health state of infrastructure dependencies (e.g., database, Redis) and proceed with job execution only when the health check status is Healthy.

2. Deployment Coordination with Kubernetes Readiness Probes
   The Kubernetes readiness probe is configured with a 90-second initial delay due to the service's startup time. During deployment, both the old and new pod instances run concurrently. I would like to pause the HostedService execution loop until the readiness probe indicates Healthy, ensuring the old pod has terminated and only the new pod is active.

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I think, I can contribute on that, as this seems to be quite easy.