SampleController.cs

[Produces("application/json")]
[Route("api/Sample")]
public class SampleController : Controller
{
    private readonly IHystrixCommand _hystrixCommand;

    public SampleController(IHystrixCommandFactory hystrixCommandFactory)
    {
        _hystrixCommand = hystrixCommandFactory.GetHystrixCommand("GrupoTeste", "ComandoTeste");
    }

    [HttpGet]
    public async Task<IActionResult> Get()
    {
        var result = await _hystrixCommand.ExecuteAsync(
            async () =>
            {
                var rnd = new Random();
                await Task.Delay(rnd.Next(500, 1000));

                if (rnd.Next(4) == 0) // Quando o valor for zero falha a retorna o fallback ao invés de cair na exception e retorar um server error
                {
                    throw new Exception("Exception, pode logar, porém cairá no fallback e o processo continuará normalmente...");
                }

                return "Resultado Válido";
            },
            () => Task.FromResult("Resultado Fallback"),
            new CancellationTokenSource());

        return Ok($"Hello! Resultado: {result}");
    }
}