Add /health endpoint for container health checks

[nanotaboada]

Description

Introduce a standardized health check endpoint to expose the application’s health status for monitoring and orchestration purposes. This endpoint will:

• Report overall application health and availability.
• Validate critical subsystems (e.g., database connectivity).
• Support liveness and readiness probes.
• Provide a JSON payload with detailed health information.
• Optionally integrate with a UI dashboard for visual monitoring.
• Allow unauthenticated access for monitoring tools.

Suggested Approach

1. Register health check services
   In Program.cs, add the health check services:

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddHealthChecks();

2. Map the health check endpoint
   Configure the middleware pipeline to expose /health:

var app = builder.Build();
app.MapHealthChecks("/health");
app.Run();

3. Add dependency-specific checks
   Chain additional checks for critical dependencies:

builder.Services.AddHealthChecks()
    .AddSqlServer(builder.Configuration.GetConnectionString("DefaultConnection"), name: "sql");

4. Customize JSON response
   Use HealthCheckOptions.ResponseWriter to output a structured JSON payload:

app.MapHealthChecks("/health", new HealthCheckOptions
{
    ResponseWriter = async (context, report) =>
        await CustomJsonResponseWriter(context, report)
});

5. Enable anonymous access
   Update endpoint routing or authorization policies to allow unauthenticated probes on /health (per Steve Gordon’s pattern):

app.MapHealthChecks("/health").AllowAnonymous();

6. (Optional) Integrate UI dashboard
   Add the UI viewer package and configure its endpoint for real‑time health metrics:

builder.Services.AddHealthChecksUI();
app.MapHealthChecksUI();

Acceptance Criteria

• /health responds with HTTP 200 when all checks are Healthy, and HTTP 503 when any check is Degraded or Unhealthy.
• Response includes structured JSON output with fields like status, totalDuration, and individual check details.
• At least one dependency (e.g., SQL Server) is checked and reflected in the health response.
• The /health endpoint is accessible without authentication.
• Health check configuration is manageable via appsettings.json.
• Automated tests validate Healthy, Degraded, and Unhealthy responses.

References

• 🔗 ASP.NET Core Health Checks Documentation
• 🔗 Code Maze: Health Checks in ASP.NET Core
• 🔗 Steve Gordon: Exposing Health Checks Without Authentication
• 🔗 Custom JSON ResponseWriter Example
• 🔗 AspNetCore.HealthChecks.UI GitHub