Health checks

The rule

Two questions, two endpoints, in every template that runs a web host.

Both are anonymous and answer with plain text, because Docker, load balancers and orchestrators call them without a token. Neither is traced (telemetry). The Docker image's HEALTHCHECK calls /health/live. Infrastructure owns the checks for what it talks to (AddInfrastructureHealthChecks in src/Infrastructure/DependencyInjection.cs); Presentation maps the endpoints. The Lambda template has no health endpoints, because Lambda manages its own lifecycle.

Steps

1. New external dependency in Infrastructure (a queue, another database)? Add its check inside AddInfrastructureHealthChecks and pass the tags through, so it lands on readiness.
2. Keep liveness free of dependency checks. A database outage shouldn't get the container restarted.
3. Test both endpoints with a real request (integration-tests).

Example

// src/Infrastructure/DependencyInjection.cs
public static IHealthChecksBuilder AddInfrastructureHealthChecks(this IHealthChecksBuilder builder, params string[] tags)
{
    return builder.AddDbContextCheck<MovieReviewsDbContext>("MovieReviewsDatabase", HealthStatus.Unhealthy, tags);
}

Don't

• Put a dependency check on /health/live.
• Require authentication on either endpoint.
• Return version or configuration details from a health endpoint. Anyone can call it; the version is on every span, metric and log as service.version, and behind auth at the version endpoint.

Check

dotnet test --filter "FullyQualifiedName~Health"