Bits of .NET

🏥 Health Checks = Monitoring

Apps fail silently. Health checks monitor app health. Database, cache, services — all in one.

📝 Health Check Setup

# Install package
dotnet add package Microsoft.AspNetCore.Diagnostics.HealthChecks

# Program.cs
var builder = WebApplication.CreateBuilder(args);

// Add health checks
builder.Services.AddHealthChecks()
    .AddDbContextCheck()
    .AddUrlGroup(new Uri("https://api.example.com"), "External API")
    .AddCheck("Custom")
    .AddCheck("Memory", new MemoryHealthCheck(512));

var app = builder.Build();

// Map health check endpoint
app.MapHealthChecks("/health");
app.MapHealthChecks("/health/ready", new HealthCheckOptions
{
    Predicate = _ => true
});
app.MapHealthChecks("/health/live", new HealthCheckOptions
{
    Predicate = _ => false
});

// Custom health check
public class CustomHealthCheck : IHealthCheck
{
    public Task CheckHealthAsync(
        HealthCheckContext context,
        CancellationToken cancellationToken = default)
    {
        var isHealthy = CheckSomething();
        
        if (isHealthy)
        {
            return Task.FromResult(HealthCheckResult.Healthy("Everything is working"));
        }
        
        return Task.FromResult(HealthCheckResult.Unhealthy("Something is wrong"));
    }
}

🎯 Health Check Types

// Database health
services.AddHealthChecks()
    .AddSqlServer(connectionString)
    .AddNpgSql(connectionString)
    .AddMySql(connectionString);

// Cache health
services.AddHealthChecks()
    .AddRedis(connectionString)
    .AddMemoryCache();

// HTTP health
services.AddHealthChecks()
    .AddUrlGroup(new Uri("https://api.example.com"))
    .AddUrlGroup(new Uri("https://cdn.example.com"));

// Custom health with DI
public class DatabaseHealthCheck : IHealthCheck
{
    private readonly AppDbContext _context;
    
    public DatabaseHealthCheck(AppDbContext context)
    {
        _context = context;
    }
    
    public async Task CheckHealthAsync(
        HealthCheckContext context,
        CancellationToken cancellationToken)
    {
        try
        {
            await _context.Database.CanConnectAsync(cancellationToken);
            return HealthCheckResult.Healthy("Database is healthy");
        }
        catch (Exception ex)
        {
            return HealthCheckResult.Unhealthy("Database is unhealthy", ex);
        }
    }
}

// Health Check Tips
- Check all critical dependencies
- Use separate endpoints (liveness/readiness)
- Monitor in Kubernetes
- Log health check results
- Set appropriate timeouts

💡 Health Check Tips

• Check all critical dependencies
• Use separate endpoints (liveness/readiness)
• Monitor in Kubernetes
• Log health check results
• Set appropriate timeouts