In this blog I will try to explain how one can create clean and effective policies to retry API calls and have fallbacks when requests are failing. With Polly it is possible to create complex and advanced scenarios for error handling with just a few lines of code.

This week I was connecting an eCommerce web application to an ERP system with REST APIs. There are multiple endpoints, all authenticated with OAuth. To make sure all calls to the APIs will have a high success rate I had to implement retry mechanisms for different scenarios.

For this kind of scenarios there is a very cool library: Polly which I have been using for some years now (together with Refit ) and I am just deeply in love with both libraries.

Although there are abundant resources about Polly on the web I wanted to write a post with a lot of sample code to provide a quick and practical example of how easy it is to use Polly to create advanced exception handling with APIs. I am using Refit because it is quick and easy to use with REST APIs but Polly can be used with any kind of C# code.

Disclaimer: this article and sample code have nothing to do with the work I did for the eCommerce website. It was just a trigger for me to write about Polly . Also, the shown code might not always show the best way to implementat things, it is just an example to explain some use cases of Polly .

What is Polly?

From the Polly repository : Polly is a .NET resilience and transient-fault-handling library that allows developers to express policies such as Retry, Circuit Breaker, Timeout, Bulkhead Isolation, and Fallback in a fluent and thread-safe manner.

How a simple API call can get way too complex

Let’s say I have a micro service with an API endpoint to retrieve products: