how it works health checks

Health Checks

Since the subsystems provide a mindmap for each dependency, it isn't necessary to discuss it here

What's important is to provide liveness and health check samples, as well as a diagram demonstrating the flow of the calls from the health checks ui

How It's Added and Mapped

Health checks are added to IHealthChecksBuilder and added to the services collection

// This isn't exactly how it's added in this codebase and is here for demonstration purposes
builder.Services.AddHealthChecks()
    .AddCheck(
        name: "self", 
        check: () => HealthCheckResult.Healthy(),
        tags: new[] { "self" });

Two endpoints are mapped for health checks, one for liveness [check on self] and one for health [check on self and all dependencies]

public static WebApplication MapCommonHealthChecks(this WebApplication app)
{
    app.MapHealthChecks(app.Configuration["HealthCheckEndpoint"]!, new HealthCheckOptions
    {
        ResponseWriter = UIResponseWriter.WriteHealthCheckUIResponse
    });

    app.MapHealthChecks(app.Configuration["LivenessCheckEndpoint"]!, new HealthCheckOptions
    {
        Predicate = healthCheckRegistration => healthCheckRegistration.Tags.Contains("self"),
        ResponseWriter = UIResponseWriter.WriteHealthCheckUIResponse
    });

    return app;
}

Samples

These are from the Mvc Frontend

Liveness

{
  "status": "Healthy",
  "totalDuration": "00:00:00.0001447",
  "entries": {
    "self": {
      "data": {},
      "duration": "00:00:00.0000154",
      "status": "Healthy",
      "tags": [
        "self"
      ]
    }
  }
}

Health

{
  "status": "Healthy",
  "totalDuration": "00:00:00.0237445",
  "entries": {
    "self": {
      "data": {},
      "duration": "00:00:00.0000061",
      "status": "Healthy",
      "tags": [
        "self"
      ]
    },
    "identityServer": {
      "data": {},
      "duration": "00:00:00.0236168",
      "status": "Healthy",
      "tags": []
    },
    "gateway": {
      "data": {},
      "duration": "00:00:00.0174471",
      "status": "Healthy",
      "tags": []
    }
  }
}

Sequence Diagram

One thing I wished was the case with the health checks ui is that it did the checks in parallel, but unfortunately it does it one after the other in the order it's defined in app settings

sequenceDiagram
    participant healthchecksui as Health Checks UI
    participant mvc as Mvc Frontend
    participant webbff as Web Backend-For-Frontend
    participant addressservice as Address Service
    participant addressworker as Address Worker
    participant identityservice as Identity Service
    participant orderservice as Order Service
    participant orderworker as Order Worker
    participant tyresservice as Tyres Service
    loop Every 30 seconds
        healthchecksui ->> mvc: /health/liveness
        mvc -->> healthchecksui: 200 OK 
        healthchecksui ->> webbff: /health/liveness
        webbff -->> healthchecksui: 200 OK 
        healthchecksui ->> addressservice: /health/liveness
        addressservice -->> healthchecksui: 200 OK 
        healthchecksui ->> addressworker: /health/liveness
        addressworker -->> healthchecksui: 200 OK 
        healthchecksui ->> identityservice: /health/liveness
        identityservice -->> healthchecksui: 200 OK 
        healthchecksui ->> orderservice: /health/liveness
        orderservice -->> healthchecksui: 200 OK 
        healthchecksui ->> orderworker: /health/liveness
        orderworker -->> healthchecksui: 200 OK 
        healthchecksui ->> tyresservice: /health/liveness
        tyresservice -->> healthchecksui: 200 OK 
        healthchecksui ->> mvc: /health
        mvc -->> healthchecksui: 200 OK 
        healthchecksui ->> webbff: /health
        webbff -->> healthchecksui: 200 OK 
        healthchecksui ->> addressservice: /health
        addressservice -->> healthchecksui: 200 OK 
        healthchecksui ->> addressworker: /health
        addressworker -->> healthchecksui: 200 OK 
        healthchecksui ->> identityservice: /health
        identityservice -->> healthchecksui: 200 OK 
        healthchecksui ->> orderservice: /health
        orderservice -->> healthchecksui: 200 OK 
        healthchecksui ->> orderworker: /health
        orderworker -->> healthchecksui: 200 OK 
        healthchecksui ->> tyresservice: /health
        tyresservice -->> healthchecksui: 200 OK
    end

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