How to register different services for different environments in ASP.NET MVC 6?

Question

What is the right way to configure services for different environments?

For example I want to add FakeService to services collection for DEV configuration and RealService for Release configuration.

public void ConfigureServices(IServiceCollection services)
{
    /* Need to check environment */
    services.AddSingleton<IService, FakeService>();
    ....
}

Answer 1

MVC 6 has a value that defines what environment it is, this can be set by the environment variable ASPNET_ENV. You can grab that value from IHostingEnvironment:

public void ConfigureServices(IServiceCollection services)
{
    var env = services.BuildServiceProvider().GetRequiredService<IHostingEnvironment>();
    if (env.IsDevelopment())
        Console.WriteLine("Development");
    else if (env.IsProduction())
        Console.WriteLine("Production");
    else if (env.IsEnvironment("MyCustomEnvironment"))
        Console.WriteLine("MyCustomEnvironment");
}

You can set the value in VS2015 on your project by Right-click > Properties > Debug > Environment Variables:

Here's some more info on configuring with environment variables.

Answer 2

It's just a matter of reading this from your configuration file, and making a decision in code accordingly:

bool isDev = Boolean.Parse(ConfigurationManager.AppSettings["IsDev"]);

if (isDev) {
    services.AddSingleton<IService, FakeService>();
} else {
    services.AddSingleton<IService, RealService>();
}

Another option is to use compiler directives:

if #DEBUG
    services.AddSingleton<IService, FakeService>();
#else
    services.AddSingleton<IService, RealService>();
#endif