How to ensure API is "warmed up" before first request?

Question

I have a xamarin android app that makes requests to an api hosted on .net core (on IIS on Windows Server). Initial requests ALWAYS take a long time to load (presumably because of some warmup process). How do I ensure that the API is ready to go by the time the user needs to make a request?

Do I just make rapid async get/post requests on app startup? This seems in-efficient...

Answer 1

You need to use health check for your API:

public class ExampleHealthCheck : IHealthCheck
{
    public ExampleHealthCheck()
    {
        // Use dependency injection (DI) to supply any required services to the
        // "warmed up" check.
    }

    public Task<HealthCheckResult> CheckHealthAsync(
    HealthCheckContext context, 
         CancellationToken cancellationToken = default(CancellationToken))
    {
        // Execute "warmed up" check logic here.

        var healthCheckResultHealthy = true;

        if (healthCheckResultHealthy)
        {
            return Task.FromResult(
            HealthCheckResult.Healthy("The check indicates a healthy result."));
        }

        return Task.FromResult(
        HealthCheckResult.Unhealthy("The check indicates an unhealthy result."));
    }
}

Add your service to health check services:

public void ConfigureServices(IServiceCollection services)
{
    services.AddHealthChecks()
        .AddCheck<ExampleHealthCheck>("example_health_check");
}

In Startup.Configure, call UseHealthChecks in the processing pipeline with the endpoint URL:

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.UseHealthChecks("/health");
}

Link to documentation: https://learn.microsoft.com/ru-ru/aspnet/core/host-and-deploy/health-checks?view=aspnetcore-2.2