Section 5 of 6

Health Checks

🎯 What You'll Learn

What are health checks
Basic health checks
Database health checks
Custom health checks
Health check UI

What are Health Checks?

Health checks monitor the health of your application and its dependencies (database, external APIs, etc.) to ensure everything is working correctly.

Basic Health Check

Program.cs C#

builder.Services.AddHealthChecks();

var app = builder.Build();

app.MapHealthChecks("/health");

Test Health Check Bash

curl https://localhost:5001/health

Database Health Check

Install Package Bash

dotnet add package AspNetCore.HealthChecks.SqlServer

Program.cs C#

builder.Services.AddHealthChecks()
    .AddSqlServer(builder.Configuration.GetConnectionString("DefaultConnection"));

Custom Health Check

StockHealthCheck.cs C#

public class StockHealthCheck : IHealthCheck
{
    private readonly InvenTrackDbContext _context;

    public StockHealthCheck(InvenTrackDbContext context)
    {
        _context = context;
    }

    public async Task<HealthCheckResult> CheckHealthAsync(
        HealthCheckContext context, 
        CancellationToken cancellationToken = default)
    {
        try
        {
            var lowStockCount = await _context.Products
                .CountAsync(p => p.Quantity < p.ReorderLevel, cancellationToken);

            if (lowStockCount > 10)
            {
                return HealthCheckResult.Degraded(
                    $"{lowStockCount} products have low stock");
            }

            return HealthCheckResult.Healthy("Stock levels are good");
        }
        catch (Exception ex)
        {
            return HealthCheckResult.Unhealthy("Stock check failed", ex);
        }
    }
}

builder.Services.AddHealthChecks()
    .AddCheck<StockHealthCheck>("stock_check");

Health Check Response

Custom Response Writer C#

using Microsoft.Extensions.Diagnostics.HealthChecks;

app.MapHealthChecks("/health", new HealthCheckOptions
{
    ResponseWriter = async (context, report) =>
    {
        context.Response.ContentType = "application/json";
        
        var result = JsonSerializer.Serialize(new
        {
            status = report.Status.ToString(),
            checks = report.Entries.Select(e => new
            {
                name = e.Key,
                status = e.Value.Status.ToString(),
                description = e.Value.Description
            })
        });
        
        await context.Response.WriteAsync(result);
    }
});

Health Check UI

Install Package Bash

dotnet add package AspNetCore.HealthChecks.UI
dotnet add package AspNetCore.HealthChecks.UI.InMemory.Storage

Program.cs C#

builder.Services.AddHealthChecksUI().AddInMemoryStorage();

app.MapHealthChecksUI();

appsettings.json JSON

{
  "HealthChecksUI": {
    "HealthChecks": [
      {
        "Name": "InvenTrack",
        "Uri": "https://localhost:5001/health"
      }
    ],
    "EvaluationTimeInSeconds": 10
  }
}

Access UI at: https://localhost:5001/healthchecks-ui

Key Takeaways

Health checks: Monitor application health
AddHealthChecks(): Register service
MapHealthChecks(): Expose endpoint
Database checks: AddSqlServer()
Custom checks: Implement IHealthCheck
Health Check UI: Visual dashboard