AspNetCore.Live.Api.HealthChecks.Server 1.6.0

LiveHealthChecks

Real-Time Api Health Check Monitoring

Packages	Version & Downloads
AspNetCore.Live.Api.HealthChecks.Server
AspNetCore.Live.Api.HealthChecks.Client

Background

An Asp Net Core Web Api has a Health Checks system built into it.

This project taps into that system & makes the generated Health Report,

available to Monitoring applications, in real-time.

The Client package, installed in the Api, runs the Health Check periodically,

and uploads the generated Health Report to the Server SignalR Hub.

The Hub sends a web socket push notification to the connected clients,

notifying them of the Health Report in real-time.

System Architecture

The system can comprise of multiple APIs & multiple Monitoring Apps.

All connecting to the same Server Hub.

Each Api Client has a ReceiveMethod & SecretKey.

The ReceiveMethod is the method, the Monitoring apps have to listen to.

All Health Reports of that Api are published to this ReceiveMethod.

The Server has to be set up for each Api Client's ReceiveMethod & SecretKey.

When a connection request is made to the Server, the ReceiveMethod & SecretKey have to be provided in custom headers.

All connections to the Server (from the Api Client & Monitoring apps) are authorized using ReceiveMethod & SecretKey.

Server

You can use a Console app as a Health Checks Server.

Just create one with Web Sdk (project file):

<Project Sdk="Microsoft.NET.Sdk.Web">

Then, plug in the Server package.

var builder = WebApplication.CreateBuilder();

builder.Services.AddSignalR();

//Load the Clients dynamically
builder.Services.AddScoped<IClientsService, ClientsService>();
builder.Services.AddLiveHealthChecksServer();

var app = builder.Build();

app.UseRouting();
app.UseEndpoints(endpoints =>
{
    endpoints.MapHub<LiveHealthChecksHub>("/livehealthcheckshub");
});

app.Run();

A Client (Api) with a ReceiveMethod & SecretKey are set up in the Server.

The Api publishes to the Server with this information.

The Server sends push notification to the ReceiveMethod, if the Client's SecretKey matches that on the Server.

You implement Server interface IClientsService to get the list of Clients.

The list can be stored in a database table (for eg.).

You could fetch the list from the database & cache it.

This way you do not need a Server shutdown to add a new Client Api to the system.

Sample ClientsService

    public class ClientsService : IClientsService
    {
        public async Task<ClientSettings[]> GetClientsAsync()
        {
            //The Clients list below is hard-coded but,
            //You can fetch the Clients from a database (for eg.) and
            //You can cache the Clients too.
            return await Task.FromResult(new ClientSettings[]
            {
                new ClientSettings
                {
                    ReceiveMethod = "SampleApiHealth",
                    SecretKey = "43bf0968-17e0-4d22-816a-6eaadd766692"
                },
                //Optional
                //Monitoring app connecting with ReceiveMethod *
                //will receive notifications for all ReceiveMethods in the system.
                new ClientSettings {
                    ReceiveMethod = "*",
                    SecretKey = "f22f3fd2-687d-48a1-aa2f-f2c9181364eb"
                }
            });
        }
    }

Asp Net Core Api

In your Api add the Client Nuget package.

then

builder.Services.AddHealthChecks() //Required - add all your health checks
                .AddLiveHealthChecksClient(settings =>
                {
                    //You can set the health check interval
                    //by a Cron Expression. 
                    settings.HealthCheckIntervalCronExpression = "0 * * * *";
                    //Or in minutes
                    //settings.HealthCheckIntervalInMinutes = 60;
                    //Providing ClientId is optional. Good for tracking in the logs.
                    settings.ClientId = "SampleApi";
                    settings.ReceiveMethod = "SampleApiHealth";
                    settings.HealthCheckServerHubUrl = "https://localhost:5001/livehealthcheckshub";
                    settings.SecretKey = "43bf0968-17e0-4d22-816a-6eaadd766692";
                    settings.PublishOnlyWhenNotHealthy = false;
                    //Optional - transform your health report to as you want it published.
                    settings.TransformHealthReport = healthReport => new
                    {
                        status = healthReport.Status.ToString(),
                        results = healthReport.Entries.Select(e => new
                        {
                            key = e.Key,
                            value = e.Value.Status.ToString()
                        })
                    };
                });

The ReceiveMethod is the SignalR method that Monitoring app needs to listen to.

The SecretKey must be the same between Server & Api.

Set PublishOnlyWhenNotHealthy to true if you want to publish anomalies,

ie those Health Reports with not Healthy status.

The Server sends the Health Report as a real-time push notification.

Note:- You can host a Server & Client in the same Api too.

Monitoring app

In your Monitoring app, create a SignalR connection to the Server Hub.

Then, start listening to the set ReceiveMethod ie "SampleApiHealth".

Set the Headers as shown. Use the same ReceiveMethod & SecretKey.

var connection = new HubConnectionBuilder()
                        .WithUrl("https://localhost:5001/livehealthcheckshub", o =>
                        {
                            o.Headers.Add("LiveHealthChecks-ReceiveMethod", "SampleApiHealth");
                            o.Headers.Add("LiveHealthChecks-SecretKey", "43bf0968-17e0-4d22-816a-6eaadd766692");
                            //Optional - value can be anything you want. good for tracking in the logs.
                            o.Headers.Add("LiveHealthChecks-ClientId", "Monitoring App 1");
                        })
                        .WithAutomaticReconnect()
                        .Build();

connection.On<string>("SampleApiHealth", report =>
{
    Console.WriteLine(report);
});

await connection.StartAsync();

If you want to receive notifications for all ReceiveMethods in the system, on the same connection,

set the ReceiveMethod header to * & use the SecretKey set in the Server.

var connection = new HubConnectionBuilder()
                        .WithUrl("https://localhost:5001/livehealthcheckshub", o =>
                        {
                            o.Headers.Add("LiveHealthChecks-ReceiveMethod", "*");
                            o.Headers.Add("LiveHealthChecks-SecretKey", "f22f3fd2-687d-48a1-aa2f-f2c9181364eb");
                            //Optional - value can be anything you want. good for tracking in the logs.
                            o.Headers.Add("LiveHealthChecks-ClientId", "Monitoring App 1");
                        })
                        .WithAutomaticReconnect()
                        .Build();

connection.On<string>("SampleApiHealth", report =>
{
    Console.WriteLine(report);
});

connection.On<string>("SampleApi2Health", report =>
{
    Console.WriteLine(report);
});

await connection.StartAsync();

Live - Trigger & publish Health Checks

Besides, the Client package running the Health Check on the Api itself, periodically,

you can run a Health Check and publish the Health Report to the Server.

You can trigger a Health Check, at any point, from anywhere, in your API,

by injecting the Client package's IMyHealthCheckService interface and,

calling the CheckHealthAsync method.

This method is a wrapper around the built-in Health Check system's HealthCheckService.

and then, publish the generated Health Report to the Server yourself,

by calling the PublishHealthReportAsync method.