c# - How do I use the new resilience strategy in polly.core to a fallback strategy with custom action? - Stack Overflow

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I have an older policy that fallsback to a custom action.

// Several other overloads including one that's synchronous and has `void` as a return type. 
// Required as some of our older services have not been asyncified yet
public void RetryWithPolicy(Action action) { 
    var policy = Policy.Handle<BrokenCircuitException>()
                                 .Fallback(_ => action())
                                 .Wrap(someCircuitBreakerPolicy)
                                 .Wrap(someWaitAndRetryPolicy);

    policy.Execute(action);
}

I'm unable to find a way to do this using the new resilience strategy properly? Is the correct way to add a hedging strategy that allows the callback to be re-executed? Looking at the fallback strategy, I wasn't able to find a way to execute the callback?

I have an older policy that fallsback to a custom action.

// Several other overloads including one that's synchronous and has `void` as a return type. 
// Required as some of our older services have not been asyncified yet
public void RetryWithPolicy(Action action) { 
    var policy = Policy.Handle<BrokenCircuitException>()
                                 .Fallback(_ => action())
                                 .Wrap(someCircuitBreakerPolicy)
                                 .Wrap(someWaitAndRetryPolicy);

    policy.Execute(action);
}

I'm unable to find a way to do this using the new resilience strategy properly? Is the correct way to add a hedging strategy that allows the callback to be re-executed? Looking at the fallback strategy, I wasn't able to find a way to execute the callback?

• c#
• -core
• fallback
• polly
• retry-logic

Share Improve this question Follow edited Feb 25 at 9:17 Peter Csala 22.8k1616 gold badges4848 silver badges9292 bronze badges asked Feb 25 at 2:15 SamIAmSamIAm 2,48977 gold badges3838 silver badges5555 bronze badges 1

• @SamlAm Did my proposed solution help you to solve your issue? Do you have further questions? – Peter Csala Commented Feb 27 at 8:02

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1 Answer 1

Sorted by: Reset to default 0

In case of V8 the top-level data structure is the ResiliencePipeline. In order to create a pipeline, you should use the ResiliencePipelineBuilder to register multiple changed strategies. (In V8 the resilience patterns are called strategies, whereas in V7 they are called policies.) So, there is no Wrap{Async} concept in V8.

Here is an example how to chain together a fallback and retry: (I've omitted the circuit breaker from the setup for the sake of simplicity.)

public static void Main()
{
    var shouldHandle= new PredicateBuilder<HttpResponseMessage>()
        .HandleResult(r => r.StatusCode == HttpStatusCode.InternalServerError);

    var pipeline = new ResiliencePipelineBuilder<HttpResponseMessage>()
        .AddFallback(new()
        {
            ShouldHandle = shouldHandle,
            FallbackAction = static args => Outcome.FromResultAsValueTask(ResolveFallbackResponse(args.Outcome))
        })
        .AddRetry(new()
        {
           ShouldHandle = shouldHandle,
           MaxRetryAttempts = 3,
           Delay = TimeSpan.FromSeconds(0.5),
        })
        .Build();

    var result = pipeline.Execute(() => new HttpResponseMessage(HttpStatusCode.InternalServerError));
    result.StatusCode.Dump();
}

static HttpResponseMessage ResolveFallbackResponse(Outcome<HttpResponseMessage> outcome)
    => new HttpResponseMessage(HttpStatusCode.RequestTimeout);

• I've extracted the predicate when to trigger retry and fallback
• The fallback action is also extracted into a dedicated method ResolveFallbackResponse
• A retry and a fallback are chained together

I suggest checking the following documentation pages where we have tried to easy to use examples:

• https://www.pollydocs./pipelines/index.html
• https://www.pollydocs./strategies/index.html
• https://www.pollydocs./migration-v8.html#migrating-policy-wrap
• https://www.pollydocs./strategies/retry.html
• https://www.pollydocs./strategies/fallback.html

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