All 15 Health Checks questions
More in Health Checks
What is the ASP.NET Core Health Checks middleware, and what problem does it solve? What HTTP status code does the health check middleware return by default for each status (Healthy, Degraded, Unhealthy)? How do you customize the JSON response format of the health check endpoint, since the default output is just plain text status? How do you add pre-built health checks for common external dependencies like SQL Server, Redis, or a URL endpoint, using the community AspNetCore.Diagnostics.HealthChecks packages? How do health checks interact with dependency injection scoping, particularly for checks that need a scoped service like a DbContext? Why should the detailed /health endpoint (with full dependency status breakdown) generally not be exposed publicly on the internet, and how do you restrict access to it? How would you write an integration test verifying that your health check endpoint correctly reports Unhealthy when a dependency is down? How would you exclude health check endpoints from other cross-cutting middleware like authentication, logging, or rate limiting that shouldn't apply to frequent automated health polling? How do you differentiate liveness and readiness health checks using tags, and why does Kubernetes treat these two probe types differently? How would you implement a health check that reports Degraded (rather than a binary Healthy/Unhealthy) based on a performance threshold, like elevated database query latency?
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ASP.NET Core › Health Checks

How do you implement a custom health check by implementing IHealthCheck, such as checking database connectivity?

Intermediate

Answer

Implement IHealthCheck's single CheckHealthAsync method, returning HealthCheckResult.Healthy(), .Degraded(), or .Unhealthy() (each optionally with a description and data dictionary) based on whatever logic determines the dependency's status -- register it via AddHealthChecks().AddCheck<T>("name") or the inline AddCheck("name", () => ...) overload for simple synchronous checks.
public class DatabaseHealthCheck(AppDbContext db) : IHealthCheck {
    public async Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken ct = default) {
        try {
            await db.Database.CanConnectAsync(ct);
            return HealthCheckResult.Healthy("Database connection OK");
        } catch (Exception ex) {
            return HealthCheckResult.Unhealthy("Database connection failed", ex);
        }
    }
}

builder.Services.AddHealthChecks()
    .AddCheck<DatabaseHealthCheck>("database");
Real-world example An e-commerce API registers a custom DatabaseHealthCheck verifying it can actually connect to the database (not just that the connection string is configured), causing the /health endpoint to report Unhealthy during a database outage even while the app process itself is still running fine.

Common follow-ups: What's the difference between Degraded and Unhealthy, and how should consumers of the health endpoint react differently to each?;How do you set a timeout for an individual health check so a hanging dependency doesn't block the whole endpoint?

Configuration & Options Pattern;Dependency Injection
All 15 Health Checks questions