A circuit breaker monitors the number of failed requests and decides to delay sending further requests based on configurable threshold. Read more about circuit breakers. Failure threshold, delay time, failure criteria, and event listeners are configurable in config file and code.

Our solution has been powering Scala services in production. It's battle tested and proven.

build.sbt

resolvers += Resolver.jcenterRepo // Adds Bintray to resolvers
libraryDependencies ++= Seq("com.hootsuite" %% "scala-circuit-breaker" % "1.x.x")

Use CircuitBreakerBuilder to initialize circuit breaker:

Configure circuit breaker in reference.conf

circuit-breaker {
  fail-limit = 5 # maximum number of consecutive failures before the circuit breaker is tripped (opened)
  retry-delay = 10 seconds # duration until an open/broken circuit breaker lets a call through to verify whether or not it should be reset
}

Optionally, define the following:

• a partial function that determines what should be considered as failures

• a partial function that determines what exceptions that should NOT be considered as failures

• listeners that will be notified when the circuit breaker changes state (open <--> closed)

• listeners that will be notified whenever the circuit breaker handles a method/function call

def circuitBreakerBuilder(name: String): CircuitBreakerBuilder = {
    new CircuitBreakerBuilder(
      name = name,
      failLimit = config.getInt("circuit-breaker.fail-limit"),
      retryDelay = Duration(config.getDuration("circuit-breaker.retry-delay", TimeUnit.SECONDS), TimeUnit.SECONDS))
      .withNonFailureExceptionCases {
        // Ignore 4xx level responses
        case _: BadRequest => true
        case _: Unauthorized => true
        case _: NotFound => true
      }
      .withStateChangeListeners(stateChangeListeners)
      .withInvocationListeners(invocationListeners)
  }

See scala-circuit-breaker-example

Contribute by submitting a PR and a bug report in GitHub.

Diego Alvarez @d1egoaz

Andres Rama @andres_rama_hs

Steve Song @ssongvan

Tatsuhiro Ujihisa @ujm

Johnny Bufu

scala-circuit-breaker is Open Source and available under the Apache 2 License.

This project took inspiration from Sentries which has a BSD 2-Clause License, our solution includes ability to fine-tune what should be considered as failures. It also has hooks when circuit breaker states change.