resilience

Resilience Patterns (Polly v8)

Reference for building fault-tolerant .NET services using Polly v8 and Microsoft.Extensions.Resilience. Used by dnp-planner and dnp-tdd-developer-hard.

Package Reference

<PackageReference Include="Microsoft.Extensions.Resilience" Version="9.*" />
<!-- For HTTP clients: -->
<PackageReference Include="Microsoft.Extensions.Http.Resilience" Version="9.*" />

Breaking change from Polly v7: the Policy.Handle<>().Retry() API is gone. Use ResiliencePipelineBuilder exclusively.

Core Concepts

Strategies execute in the order they are added. Outer strategies wrap inner ones — add timeout last to apply it per-attempt, or first to apply it to the whole pipeline.

DI Registration

builder.Services.AddResiliencePipeline("database", pipeline =>
    pipeline
        .AddRetry(new RetryStrategyOptions
        {
            MaxRetryAttempts = 3,
            Delay = TimeSpan.FromSeconds(1),
            BackoffType = DelayBackoffType.Exponential,
            UseJitter = true,
            ShouldHandle = new PredicateBuilder()
                .Handle<SqlException>()
                .Handle<TimeoutException>(),
            OnRetry = args =>
            {
                // args.Context, args.AttemptNumber, args.Outcome available
                Console.WriteLine($"Retry {args.AttemptNumber} after {args.RetryDelay}");
                return ValueTask.CompletedTask;
            }
        })
        .AddCircuitBreaker(new CircuitBreakerStrategyOptions
        {
            FailureRatio = 0.5,
            SamplingDuration = TimeSpan.FromSeconds(30),
            MinimumThroughput = 5,
            BreakDuration = TimeSpan.FromSeconds(15)
        })
        .AddTimeout(TimeSpan.FromSeconds(5)));