Create Gateway Service with .NET

// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
    services.AddCors();

    services.AddControllers().AddJsonOptions(options=>
    {
            options.JsonSerializerOptions.IgnoreNullValues = true;
    });

    services.AddHealthChecks();
    services.AddControllersWithViews();
}

// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{

    ProductsController.Config();

    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }

    app.UseCors(builder => builder
            .AllowAnyOrigin ()
            .AllowAnyHeader ()
            .AllowAnyMethod ());

    app.UseHealthChecks("/health");

    app.UseRouting();
    app.UseDefaultFiles();
    app.UseStaticFiles();

    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllers();
        endpoints.MapControllerRoute(
            name: "default",
            pattern: "{controller=Home}/{action=Index}/{id?}");
    });

}

[ApiController]
[Route("api/[controller]")] (1)
public class ProductsController : ControllerBase
{
    [HttpGet]
    public IEnumerable<Products> Get()
    {
        private static HttpClient catalogHttpClient = new HttpClient(); (4)
        private static HttpClient inventoryHttpClient = new HttpClient();

        try
        {
            // get the product list
            IEnumerable<Products> productsList = GetCatalog(); (2)

            // update each item with their inventory value
            foreach(Products p in productsList) (3)
            {
                Inventory inv = GetInventory(p.ItemId);
                if (inv != null)
                    p.Availability = new Availability(inv);
            }

            return productsList;
        }
        catch(Exception e)
        {
            Console.WriteLine("Using Catalog service: " + catalogApiHost + " and Inventory service: " + inventoryApiHost);
            Console.WriteLine("Failure to get service data: " + e.Message);
            // on failures return error
            throw e;
        }
    }

    private IEnumerable<Products> GetCatalog()
    {
        var data = catalogHttpClient.GetStringAsync("/api/catalog").Result;
        return JsonConvert.DeserializeObject<IEnumerable<Products>>(data);
    }

    private Inventory GetInventory(string itemId)
    {
        var data = inventoryHttpClient.GetStringAsync("/api/inventory/" + itemId).Result;
        return JsonConvert.DeserializeObject<Inventory>(data);
    }

}

[ {
  "itemId" : "329299",
  "name" : "Red Fedora",
  "desc" : "Official Red Hat Fedora",
  "price" : 34.99,
  "availability" : {
    "quantity" : 35
  }
},
...
]

public static void Config()
{
    try
    {
        // discover the URL of the services we are going to call
        catalogApiHost = "http://" +
            Environment.GetEnvironmentVariable("CATALOG_COOLSTORE_SERVICE_HOST") + ":" +
            Environment.GetEnvironmentVariable("CATALOG_COOLSTORE_SERVICE_PORT");

        inventoryApiHost = "http://" +
            Environment.GetEnvironmentVariable("INVENTORY_COOLSTORE_SERVICE_HOST") + ":" +
            Environment.GetEnvironmentVariable("INVENTORY_COOLSTORE_SERVICE_PORT");

        // set up the Http conection pools
        inventoryHttpClient.BaseAddress = new Uri(inventoryApiHost);
        catalogHttpClient.BaseAddress = new Uri(catalogApiHost);
    }