Polly

Polly Documentation

Polly is a .NET resilience and transient-fault-handling library that allows developers to express resilience strategies such as Retry, Circuit Breaker, Hedging, Timeout, Rate Limiter and Fallback in a fluent and thread-safe manner.

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Quick start

To use Polly, you must provide a callback and execute it using resilience pipeline. A resilience pipeline is a combination of one or more resilience strategies such as retry, timeout, and rate limiter. Polly uses builders to integrate these strategies into a pipeline.

To get started, first add the Polly.Core package to your project by running the following command:

dotnet add package Polly.Core

You can create a ResiliencePipeline using the ResiliencePipelineBuilder class as shown below:

// Create a instance of builder that exposes various extensions for adding resilience strategies
var builder = new ResiliencePipelineBuilder();

// Add retry using the default options
builder.AddRetry(new RetryStrategyOptions());

// Add 10 second timeout
builder.AddTimeout(TimeSpan.FromSeconds(10));

// Build the resilience pipeline
ResiliencePipeline pipeline = builder.Build();

// Execute the pipeline
await pipeline.ExecuteAsync(async token =>
{
    // Your custom logic here
});

Dependency injection

If you prefer to define resilience pipelines using IServiceCollection, you’ll need to install the Polly.Extensions package:

dotnet add package Polly.Extensions

You can then define your resilience pipeline using the AddResiliencePipeline(...) extension method as shown:

var services = new ServiceCollection();

// Define a resilience pipeline with the name "my-pipeline"
services.AddResiliencePipeline("my-pipeline", builder =>
{
    builder
        .AddRetry(new RetryStrategyOptions())
        .AddTimeout(TimeSpan.FromSeconds(10));
});

// Build the service provider
IServiceProvider serviceProvider = services.BuildServiceProvider();

// Retrieve ResiliencePipelineProvider that caches and dynamically creates the resilience pipelines
var pipelineProvider = serviceProvider.GetRequiredService<ResiliencePipelineProvider<string>>();

// Retrieve resilience pipeline using the name it was registered with
ResiliencePipeline pipeline = pipelineProvider.GetPipeline("my-pipeline");

// Execute the pipeline
await pipeline.ExecuteAsync(async token =>
{
    // Your custom logic here
});

Resilience strategies

Strategy Reactive Premise AKA How does the strategy mitigate?
Retry Yes Many faults are transient and may self-correct after a short delay. Maybe it’s just a blip Allows configuring automatic retries.
Circuit-breaker Yes When a system is seriously struggling, failing fast is better than making users/callers wait.

Protecting a faulting system from overload can help it recover.		 Stop doing it if it hurts

Give that system a break		 Breaks the circuit (blocks executions) for a period, when faults exceed some pre-configured threshold.
Timeout No Beyond a certain wait, a success result is unlikely. Don’t wait forever Guarantees the caller won’t have to wait beyond the timeout.
Rate Limiter No Limiting the rate a system handles requests is another way to control load.

This can apply to the way your system accepts incoming calls, and/or to the way you call downstream services.		 Slow down a bit, will you? Constrains executions to not exceed a certain rate.
Fallback Yes Things will still fail - plan what you will do when that happens. Degrade gracefully Defines an alternative value to be returned (or action to be executed) on failure.
Hedging Yes Things can be slow sometimes, plan what you will do when that happens. Hedge your bets Executes parallel actions when things are slow and waits for the fastest one.

Visit the resilience strategies section to understand their structure and explore various configuration methods.

Topics

Topics (previous Polly versions)

Samples

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