[Feature request]: Enumerate policies in ResiliencePipelineRegistry

[IGx89]

Is your feature request related to a specific problem? Or an existing feature?

Hello! In Polly v7 we have health checks in our APIs that enumerate over policies in IReadOnlyPolicyRegistry, find the circuit breaker policies, and alert if any are not open. I'm working on porting that code to Polly.Core v8 and have run into a roadblock: ResiliencePipelineRegistry doesn't implement IEnumerable nor provides any way to get a list of the pipelines. Was that removed deliberately? If not, could that functionality be added back?

If my use case above makes no sense anymore in v8, please let me know too! The migration docs were silent on this topic.

Describe the solution you'd like

ResiliencePipelineRegistry implements IEnumerable or at least adds a GetPipelines() method or similar.

Additional context

No response

[martintmk]

Hey @IGx89

In Polly V8 there is no way to retrieve the circuit breaker state from an instance of ResiliencePipeline. Even if enumerating pipeline from registry was available it wouldn't help.

What you want to do is to keep registry of CircuitBreakerStateProvider as you are creating the pipelines. See this test that demonstrates your use-case:

// Arrange
var states = new ConcurrentBag<CircuitBreakerStateProvider>();
using var registry = new ResiliencePipelineRegistry<string>();

// Act
_ = registry.GetOrAddPipeline("A", builder =>
{
    var stateProvider = new CircuitBreakerStateProvider();
    builder.AddCircuitBreaker(new() { StateProvider = stateProvider });
    states.Add(stateProvider);
});

_ = registry.GetOrAddPipeline("B", builder =>
{
    var stateProvider = new CircuitBreakerStateProvider();
    builder.AddCircuitBreaker(new() { StateProvider = stateProvider });
    states.Add(stateProvider);
});

_ = registry.TryAddBuilder("C", (builder, _) =>
{
    var stateProvider = new CircuitBreakerStateProvider();
    builder.AddCircuitBreaker(new() { StateProvider = stateProvider });
    states.Add(stateProvider);
});

// Assert
states.Should().HaveCount(2);
registry.GetPipeline("C");
states.Should().HaveCount(3);

foreach (var state in states)
{
    state.CircuitState.Should().Be(CircuitState.Closed);
}

doesn't implement IEnumerable nor provides any way to get a list of the pipelines. Was that removed deliberately? If not, could that functionality be added back?

This was deliberate choice due to dynamic nature of registry. The pipelines are not explicitly added, instead these are created on demand when requested. Additionally, with the minimal nature of ResiliencePipeline there is now way to retrieve any information about strategies from it.

Also created a PR that adds this test: #1829

[IGx89]

Thanks a lot for the detailed explanation and code example! That's very helpful. I definitely have a lot more learning to do it looks :)