Polly-Samples

This repository provides sample implementations of using the Polly library in a .NET application.

The intent of this project is to help newcomers kick-start the use of Polly within their own projects.

The samples demonstrate the policies in action, against faulting endpoints.

Projects

The solution contains three applications and one class library:

• PollyTestWebApi: This application is a web API with several endpoints. (Further information)
• PollyDemos: This library contains the Polly demos. (Further information)
• PollyTestClientConsole: This application provides a CLI to walk through the demos. (Further information)
• PollyTestClientWpf: This application provides a GUI to walk through the demos. (Further information)

flowchart LR
    console{{PollyTestClientConsole}}
    wpf{{PollyTestClientWPF}}
    lib>PollyDemos]
    api[/PollyTestWebApi\]

    console -- uses --> lib
    wpf -- uses --> lib
    lib -- invokes --> api

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Demos

General information

• The demos run against an example 'faulting server'.
  • To simulate failure, the dummy server rejects more than 3 calls in any five-second period.
• Be sure to read the <summary> at the top of each demo.
  • This explains the intent of that demo, and what resilience it adds to its handling of the calls to the 'faulting server'.
• Sometimes the <summary> also highlights what this demo doesn't achieve, which is often picked up in the following demo.
• Explore the demos in sequence for best understanding.

Sequence

#	Description	Link
00	No strategy	Code
01	Retry N times	Code
02	Wait and retry N times	Code
03	Wait and retry N times, N big enough to guarantee success	Code
04	Wait and retry forever	Code
05	Wait and retry with exponential back-off	Code
06	Wait and retry nesting circuit breaker	Code
07	Wait and retry chaining with circuit breaker by using Pipeline	Code
08	Fallback, Retry, and CircuitBreaker in a Pipeline	Code
09	Fallback, Timeout, and Retry in a Pipeline	Code
10	Without isolation: Faulting calls swamp resources, also prevent good calls	Code
11	With isolation: Faulting calls separated, do not swamp resources, good calls still succeed	Code
12	Hedging in latency mode	Code
13	Hedging in fallback mode: retry only	Code
14	Hedging in fallback mode: retry with fallback	Code
15	Hedging in parallel mode	Code
16	Entity Framework with retry N times	Code

Want further information?

• For any questions about the operation of the demos, ask on this repo with an issue.
• For any questions about Polly, ask in the Polly repository.
• For full Polly syntax, see Polly repository and the Polly documentation.

Slide decks

View the slides presented at NDC, DevIntersections and other conferences.

You are welcome to use and adapt this presentation for not-for-profit presentations of Polly to co-workers, user groups and similar, subject to the condition that references to the .NET Foundation, App-vNext and the individual members of the Polly team are retained.