rezilience is a ZIO-native collection of policies for making asynchronous systems more resilient to failures, inspired by Polly, Resilience4J and Akka.

It consists of these policies:

Policy Reactive/Proactive Description
CircuitBreaker Reactive Temporarily prevent trying calls after too many failures
RateLimiter Proactive Limit the rate of calls to a system
Bulkhead Proactive Limit the number of in-flight calls to a system
Retry Reactive Try again after transient failures
Timeout Reactive Interrupt execution if a call does not complete in time

Features / Design goals

  • Type-safety: all errors that can result from any of the rezilience policies are encoded in the method signatures, so no unexpected RuntimeExceptions.
  • Support for your own error types (the E in ZIO[R, E, A]) instead of requiring your effects to have Exception as error type
  • Lightweight: rezilience uses only ZIO fibers and will not create threads or block
  • Switchable at runtime with two transition modes
  • Resource-safe: built on ZIO’s ZManaged, any allocated resources are cleaned up safely after use.
  • Interrupt safe: interruptions of effects wrapped by rezilience policies are handled properly.
  • Thread-safe: all policies are safe under concurrent use.
  • ZIO integration: some policies take for example ZIO Schedules and rezilience tries to help type inference using variance annotations
  • Metrics: all policies (will) provide usage metrics for monitoring purposes
  • Composable: policies can be composed into one overall policy
  • Discoverable: no syntax extensions or implicit conversions, just plain scala


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Add to your build.sbt:

libraryDependencies += "nl.vroste" %% "rezilience" % "<version>"

Rezilience is available for ZIO 2 and Scala 2.13, Scala 3 and Scala.JS.

Usage example

Limit the rate of calls:

import zio._
import zio.duration._
import nl.vroste.rezilience._

def myCallToExternalResource(someInput: String): ZIO[Any, Throwable, Int] = ???

val rateLimiter: ZIO[Scope, Nothing, RateLimiter] = RateLimiter.make(max = 10, interval = 1.second)

ZIO.scoped {
  rateLimiter.flatMap { rateLimiter =>
    val result: ZIO[Any, Throwable, Int] =
      rateLimiter(myCallToExternalResource("some input"))