Understanding Polly: The .NET Resilience Library

Polly, a robust .NET library, plays a crucial role in enhancing the resilience of applications. It adeptly manages transient faults and downturns, providing developers with a suite of strategies like Retry, Circuit Breaker, Hedging, Timeout, Rate Limiter, and Fallback. These strategies help in maintaining the performance and stability of applications in the face of failures.

?What is Polly

Polly is a part of the .NET Foundation, reflecting its significance in the .NET ecosystem. It offers a fluent and thread-safe approach to applying various resilience strategies, thereby enabling applications to handle failures in an efficient manner.

Capabilities of Polly

Polly is not just about retrying failed operations. It encompasses a broader spectrum of strategies:

1. Retry: For transient problems, retrying can be an effective solution.
2. Circuit Breaker: This strategy ceases attempts when a system is broken or overloaded, aiding in recovery.
3. Timeout: This helps in aborting operations that take excessively long, freeing up resources.
4. Rate Limiter: It regulates the number of requests made or accepted, aiding in load management.
5. Fallback: Provides alternative solutions when operations fail, enhancing user experience.
6. Hedging: Executes multiple operations concurrently, choosing the fastest for better responsiveness.

Getting Started with Polly

Installing and using Polly is straightforward. By following the getting started guide, developers can integrate Polly into their projects seamlessly.

Rich Documentation

Polly's documentation is comprehensive, covering:

• Resilience Strategies: Various strategies for system improvement.
• Resilience Pipelines: Combining strategies for flexibility and reusability.
• Telemetry and Monitoring: Analyzing data generated by Polly.
• Dependency Injection: Integrating Polly with various frameworks.
• Performance: Optimization tips for best performance.
• Testing: Ensuring the reliability of resilience pipelines.
• Chaos Engineering: Using Polly for fault injection and testing system resilience.
• Extensibility: Custom strategies and extensions.
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Community Resources

Polly has a strong community presence:

• Samples: Practical examples for beginners and advanced users.
• Polly-Contrib: Enhancements and extensions from the community.
• Libraries and Contributions: Key dependencies and contributors.
• Microsoft’s eShopOnContainers: Demonstrating Polly in a .NET Microservices architecture.
• Git Workflow: Guidelines for contributing to Polly.

Practical Usage

Using Polly involves defining a callback and executing it through a resilience pipeline, which may combine strategies like retry, timeout, and rate limiter.

Example: Creating a Resilience Pipeline 

dotnet add package Polly.Core

ResiliencePipeline pipeline = new ResiliencePipelineBuilder()
    .AddRetry(new RetryStrategyOptions())
    .AddTimeout(TimeSpan.FromSeconds(10))
    .Build();

await pipeline.ExecuteAsync(static async token => { /* Custom logic */ }, cancellationToken);

Dependency Injection with Polly

For integration with IServiceCollection, use the Polly.Extensions package: 

dotnet add package Polly.Extensions

var services = new ServiceCollection();
services.AddResiliencePipeline("my-pipeline", builder =>
{
    builder.AddRetry(new RetryStrategyOptions()).AddTimeout(TimeSpan.FromSeconds(10));
});

Conclusion

Polly is an indispensable tool for .NET developers, significantly enhancing the robustness of applications. Its flexible strategies and comprehensive documentation make it a go-to library for managing transient faults and system slowdowns effectively.