Automatic Retry and Circuit Breaker made easy

Polly library logoIf you do not know Polly, you are missing out! I did not know about it until a couple of days ago and you properly never heard about it either, as this wonderful little library only has 63 downloads on NuGet at the time of writing.

Polly is an easy to use retry and circuit breaker pattern implementation for .Net – let me show you.
Start by specifying the policy – what should happen when an exception thrown:

  var policy = Policy
    .Handle<SqlException(e => e.Number == 1205) // Handling deadlock victim
    .Or<OtherException>()
    .Retry(3, (exception, retyCount, context) =>
    {
      // Log...
    });

The above policy specifies a SqlExeption with number 1205 or OtherException should be retried three times – if it still fails log and bobble the original exception up the call stack.

  var result = policy.Execute(() => FetchData(p1, p2));

It is also possible to specify the time between retries – e.g. exponential back off:

  var policy = Policy
    .Handle<MyException>()
    .WaitAndRetry(5, retryAttempt =>
      TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)
    );

Or the circuit breaker safeguarding against the same error occurs again and again if an external system is temporarily unavailable:

  var policy = Policy
    .Handle<TimeoutException>()
    .CircuitBreaker(2, TimeSpan.FromMinutes(1));

Go get it – I’m already using it 🙂

  • Patrick McElreavy

    What exactly is going on in the last example? Is it trying once, waiting for a minute, then trying a second time? Or is it trying twice, waiting for a minute, then looping back and trying twice again, then waiting for a minute, etc?

    • Break the circuit after two exceptions and keep circuit broken for one minute.