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A Tentative Comparison of Fault Tolerance Libraries on the JVM

If you're implementing microservices or not, the chances are that you're calling HTTP endpoints. With HTTP calls, a lot of things can go wrong. Experienced developers plan for this and design beyond just the happy path. In general, fault tolerance encompasses the following features:

  • Retry
  • Timeout
  • Circuit Breaker
  • Fallback
  • Rate Limiter to avoid server-side 429 responses
  • Bulkhead: Rate Limiter limits the number of calls in a determined timeframe, while Bulkhead limits the number of concurrent calls

A couple of libraries implement these features on the JVM. In this post, we will look at Microprofile Fault Tolerance, Failsafe, and Resilience4J.

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Iterate/Aggregate Fault Handling in WSO2 EI

In WSO2, we can implement the Splitter and Aggregator EIP using the Iterate and Aggregate mediators. With the Splitter pattern, we can split a message composed by different elements that need to be processed individually, and then we use the Aggregator pattern to aggregate the results of each individual call and then perform some processing over the aggregated results.

Happy Path Example

In a happy path example, all the requests and processing done inside the iterate mediator will occur with no failures, and the aggregate mediator will handle the results of all the requests made. We can see that in the proxy below: