PR to fix this is welcome.

Hello,

I've spent some time looking into this issue and have some conclusions.

I've reproduced this issue "e.map is not a function",
but I'm wondering if it's not due to a fact of misuse of HealthCheck URL and HealthCheckUI back-end URL.

app.UseHealthChecks("/health", new HealthCheckOptions { ResponseWriter = UIResponseWriter.WriteHealthCheckUIResponse });

This line configures the HealthCheck URL. So when you call /health you get a Health Check Result, also a ResponseWriter is specificed so it's formatted as nice JSON. All good.

app.MapHealthChecksUI(o => { o.UseRelativeApiPath = true; o.ApiPath = "/health"; });

This line configures HealthCheckUI back-end URL. This is the back-end URL front-end is polling to get summary of all Health Checks displayed by the UI. In this scenario, there is only one Health Check but there could be more. That's why the expected response is an array of HealthCheck results.

Please see the comparison of Health Check response vs Health Check UI back-end response

{
  "status": "Healthy",
  "totalDuration": "00:00:00.0018501",
  "entries": { /* ... */ }
}

[
    {
        "id": 1,
        "status": "Healthy",
        "onStateFrom": "2023-07-26T10:37:56.660717+02:00",
        /* ... */
     }
]

In the setup provided in the issue, identical URL is used as both Health Check URL and Health Check UI back-end URL which is incorrect.

Health Check UI back-end is iterating over all configured Health Checks and combines them in a single response (with multiple Health Check Results).

The issue can be mitigated by using any different Health Check UI back-end URL. For example:

app.MapHealthChecksUI(o => { o.UseRelativeApiPath = true; o.ApiPath = "/health-all"; });

Could you try this solution @zorgoz?

I don't think it's a bug in this package, but you can prove me wrong 😄 .

cc @sungam3r

Sorry, almost all UI stuff is out of my scope for now. So far I am not ready to discuss this area.

Hi again @zorgoz,

Any chance you could have a look if the provided answer/solution works for you?

Thanks 👍🏽

ping @zorgoz