API Gateway as a RESTful Minimal API Facade

The API Gateway is engineered as a Minimal API facade.

You can hook up Authorization, Swagger etc. just like any Minimal API.

Packages	Version	Downloads
Veritas.AspNetCore.ApiGateway.Minimal
AspNetCore.ApiGateway.Client
ts-aspnetcore-apigateway-client

Features

• Swagger
• Authorization
• Load balancing
• Response caching
• Request aggregation
• Middleware service
• Logging
• Clients available in
  • .NET
  • Typescript

Your Gateway API is a minimal API host which exposes endpoints that are a facade over your backend API endpoints.

• HEAD
• GET
• POST
• PUT
• PATCH
• DELETE

Implementation

In the solution, there are 2 back end APIs : Weather API and Stock API.

For eg. To make a GET call to the backend API, you would set up an Api and a GET Route in your Gateway API's Api Orchestrator.

Then, the client app would make a GET call to the Gateway API which would make a GET call to the backend API using HttpClient.

In your Backend API

Let us say you have a GET endpoint like this.

• HTTP GET - /weatherforecast/forecast

In your Gateway API

You add a Route for the backend GET call in the Api Orchrestrator.

You create a backend API with ApiKey called weatherservice for eg. And, a Route with RouteKey called forecast for eg.

So, the call to the Gateway would become:

• HTTP GET - /weatherservice/forecast

Add a reference to the package and...

• Create an Api Orchestration.

  You create an Api (weatherservice) and add a Route (forecast).

public static class ApiOrchestration
{
    public static void Create(IApiOrchestrator orchestrator, IApplicationBuilder app)
    {
        var serviceProvider = app.ApplicationServices;

        var weatherService = serviceProvider.GetService<IWeatherService>();

        var weatherApiClientConfig = weatherService.GetClientConfig();

        orchestrator.AddApi("weatherservice", "https://localhost:5003/")
                            //Get
                            .AddRoute("forecast", GatewayVerb.GET, new RouteInfo { Path = "weatherforecast/forecast", ResponseType = typeof(IEnumerable<WeatherForecast>) })
                            //Head
                            .AddRoute("forecasthead", GatewayVerb.HEAD, new RouteInfo { Path = "weatherforecast/forecast" })
                            //Get with params
                            .AddRoute("typewithparams", GatewayVerb.GET, new RouteInfo { Path = "weatherforecast/types/{index}" })
                            //Get using custom HttpClient
                            .AddRoute("types", GatewayVerb.GET, new RouteInfo { Path = "weatherforecast/types", ResponseType = typeof(string[]), HttpClientConfig = weatherApiClientConfig })
                            //Get with param using custom HttpClient
                            .AddRoute("type", GatewayVerb.GET, new RouteInfo { Path = "weatherforecast/types/", ResponseType = typeof(WeatherTypeResponse), HttpClientConfig = weatherApiClientConfig })
                            //Get using custom implementation
                            .AddRoute("forecast-custom", GatewayVerb.GET, weatherService.GetForecast)
                            //Post
                            .AddRoute("add", GatewayVerb.POST, new RouteInfo { Path = "weatherforecast/types/add", RequestType = typeof(AddWeatherTypeRequest), ResponseType = typeof(string[]) })
                            //Put
                            .AddRoute("update", GatewayVerb.PUT, new RouteInfo { Path = "weatherforecast/types/update", RequestType = typeof(UpdateWeatherTypeRequest), ResponseType = typeof(string[]) })
                            //Patch
                            .AddRoute("patch", GatewayVerb.PATCH, new RouteInfo { Path = "weatherforecast/forecast/patch", ResponseType = typeof(WeatherForecast) })
                            //Delete
                            .AddRoute("remove", GatewayVerb.DELETE, new RouteInfo { Path = "weatherforecast/types/remove/", ResponseType = typeof(string[]) })
                    .AddApi("stockservice", "https://localhost:5005/")
                            .AddRoute("stocks", GatewayVerb.GET, new RouteInfo { Path = "stock", ResponseType = typeof(IEnumerable<StockQuote>) })
                            .AddRoute("stock", GatewayVerb.GET, new RouteInfo { Path = "stock/", ResponseType = typeof(StockQuote) });
    }
}

• Hook up in Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    //Hook up GatewayHub using SignalR
    services.AddCors(options => options.AddPolicy("CorsPolicy", builder =>
    {
        builder
            .AllowAnyMethod()
            .AllowAnyHeader()
            .AllowAnyOrigin();
    }));

    services.AddTransient<IWeatherService, WeatherService>();

    //services.AddSingleton<IApiGatewayConfigService, ApiGatewayConfigService>(); 

    //Api gateway
    services.AddApiGateway(options =>
    {
        options.UseResponseCaching = false;
        options.ResponseCacheSettings = new ApiGatewayResponseCacheSettings
        {
            Duration = 60, //default for all routes
            Location = ResponseCacheLocation.Any,
            //Use VaryByQueryKeys to vary the response for each apiKey & routeKey
            VaryByQueryKeys = new[] { "apiKey", "routeKey" }
        };
    });

    services.AddEndpointsApiExplorer(); // Required for Minimal APIs
    services.AddSwaggerGen(c =>
    {
        c.SwaggerDoc("v1", new OpenApiInfo
        {
            Title = "My Minimal API Gateway",
            Description = "A simple example of ASP.NET Core Minimal API with Swagger",
            Version = "v1"
        });
    });

    services.AddMvc();            
}

public void Configure(IApplicationBuilder app)
{
    app.UseSwagger();
    app.UseSwaggerUI(c =>
    {
        c.SwaggerEndpoint("/swagger/v1/swagger.json", "My Minimal API Gateway V1");
        // Optional: set the UI to load at the app root URL
        // c.RoutePrefix = string.Empty; 
    });

    //webApplication.
    app.UseCors("CorsPolicy");

    //Api gateway
    app.UseApiGateway(orchestrator => ApiOrchestration.Create(orchestrator, app));

    app.UseHttpsRedirection();

    app.UseRouting();

    app.UseAuthorization();

    app.UseEndpoints(endpoints =>
    {
        // Api Gateway Minimal API
        endpoints.MapApiGatewayHead();
        endpoints.MapApiGatewayGet();
        endpoints.MapApiGatewayPost();
        endpoints.MapApiGatewayPut();
        endpoints.MapApiGatewayDelete();
        endpoints.MapApiGatewayPatch();
        endpoints.MapApiGatewayGetOrchestration();

        // Maps all the endpoints
        //endpoints.MapAllApiGatewayEndpoints();
    });
}

The Gateway Swagger appears as shown below:

To call the forecast Route on the weather service Api,

you can enter the Api key and Route key into Swagger as below:

This will hit the weatherforecast/forecast endpoint on the backend Weather API.

Using appsettings.json

If you want, you can keep the ApiKey, RouteKey, backend API base urls and Route path,

in the appsettings.json, read it using a Config Service,

and pass it to the Api Orchestrator in the Create method.

Read more.

Deployment to Prod

As with any Web API, when there is any code change, the API Gateway too is published and deployed using Blue/Green deployment.

This is available in Azure & AWS.

In Azure App Service, you use deployment slots etc.

• Read more.
• Read more.

Azure Kubernetes Service (AKS) also supports Blue/Green deployment. Read more.

In AWS, you use Elastic Beanstalk. Read more.

So, there is no down time.

Verbs usage & Routing

You can check out how the Api Gateway supported Verbs are used & Routing below.

Verbs Usage & Routing

Customizations

• Create a new or customize the default HttpClient used by all the routes, to hit the backend Api.
• Create a new or customize the default HttpClient which each route uses to hit the backend Api.
• Use your own custom implementation to hit the backend Api.

For Request aggregation, see this section.

Customizations

Load Balancing

Load Balancing

Response Caching

Response Caching

Middleware Service

Middleware Service

Clients

The Api Gateway supports a fixed set of endpoints.

All routes go through these endpoints.

The Client application has to talk to these endpoints of the Api Gateway.

A Client library is provided for:

• .Net

• Typescript

Making requests to Minimal API Gateway

These Tests show how to make calls to the Minimal API Gateway.