Round #846

Implement an IHealthCheck that returns Healthy when a TCP socket on a remote host responds within 500ms, and Unhealthy otherwise.

**TCP Health Check Implementation** ===================================== Below is an example implementation of an `IHealthCheck` that checks the health of a remote host by attempting to establish a TCP connection within a specified timeout. ```csharp using Microsoft.Extensions.Diagnostics.HealthChecks; using System; using System.Net; using System.Net.Sockets; using System.Threading; using System.Threading.Tasks; public class TcpHealthCheck : IHealthCheck { private readonly string _host; private readonly int _port; private readonly int _timeoutMs; public TcpHealthCheck(string host, int port, int timeoutMs = 500) { _host = host; _port = port; _timeoutMs = timeoutMs; } public async Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken = default) { try { using var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); var endpoint = new IPEndPoint(IPAddress.Parse(_host), _port); var task = socket.ConnectAsync(endpoint); if (await Task.WhenAny(task, Task.Delay(_timeoutMs, cancellationToken)) != task) { return HealthCheckResult.Unhealthy("TCP connection timed out"); } await task; return HealthCheckResult.Healthy("TCP connection established successfully"); } catch (SocketException ex) { return HealthCheckResult.Unhealthy($"TCP connection failed: {ex.Message}"); } catch (Exception ex) { return HealthCheckResult.Unhealthy($"An error occurred: {ex.Message}"); } } } ``` **Example Usage** ----------------- To use this health check, you can register it in the `Startup.cs` file of your ASP.NET Core application: ```csharp public void ConfigureServices(IServiceCollection services) { services.AddHealthChecks() .AddCheck<TcpHealthCheck>("tcp-check", new TcpHealthCheck("example.com", 80)); } public void Configure(IApplicationBuilder app, IWebHostEnvironment env) { app.UseRouting(); app.UseEndpoints(endpoints => { endpoints.MapHealthChecks("/health"); }); } ``` In this example, the health check will attempt to establish a TCP connection to `example.com` on port 80. If the connection is successful within the specified timeout (500ms by default), the health check will return a healthy result. Otherwise, it will return an unhealthy result. You can then access the health check results by visiting the `/health` endpoint of your application.

```csharp using System; using System.Net.Sockets; using System.Threading; using System.Threading.Tasks; using Microsoft.Extensions.Diagnostics.HealthChecks; public class TcpHealthCheck : IHealthCheck { private readonly string _host; private readonly int _port; public TcpHealthCheck(string host, int port) { _host = host; _port = port; } public async Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken = default) { try { using var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); var task = socket.ConnectAsync(_host, _port, cancellationToken); if (await Task.WhenAny(task, Task.Delay(500, cancellationToken)) == task) { await task; return HealthCheckResult.Healthy(); } else { return HealthCheckResult.Unhealthy(); } } catch (Exception ex) { return HealthCheckResult.Unhealthy(ex.Message); } } } ``` To register this health check in the DI container, you can use the following code: ```csharp services.AddHealthChecks() .AddCheck<TcpHealthCheck>("TCP Health Check", new TcpHealthCheck("remote-host", 1234)); ``` This implementation creates a TCP socket and attempts to connect to the remote host within a 500ms timeout. If the connection is successful, it returns a healthy result; otherwise, it returns an unhealthy result. The `CheckHealthAsync` method is designed to be asynchronous to avoid blocking the calling thread. The `TcpHealthCheck` class takes the remote host and port as constructor parameters, making it reusable for different hosts and ports.