1. Configuration

Project Dependencies

resilience4clj-circuitbreaker is distributed through Clojars with the identifier tessellator/resilience4clj-circuitbreaker. You can find the version information for the latest release at https://clojars.org/tessellator/resilience4clj-circuitbreaker.

The library has a hidden dependency on SLF4J, and you will need to include a dependency and related configuration for a specific logging implementation.

As an example, you could include the following in your project dependencies:

[org.slf4j/slf4j-log4j12 <VERSION>]

If you do not configure logging, you will see some SLF4J warnings output and will not receive logs the underlying circuit breaker library.

Configuration Options

The following table describes the options available when configuring circuit breakers as well as default values. A config is a map that contains any of the keys in the table. Note that a config without a particular key will use the default value (e.g., {} selects all default values).

Configuration Option	Default Value	Description
:failure-rate-threshold	50	The percentage over which the circuit breaker will trip open
:ring-buffer-size-in-half-open-state	10	The ring buffer size in the half-open state
:ring-buffer-size-in-closed-state	100	The ring buffer size in the closed state
:wait-duration-in-open-state	60000	The number of milliseconds to wait to transition from open to half-open
:automatic-transition-from-open-to-half-open-enabled	false	When true, no call is needed to occur to transition from open to half-open
:record-exceptions	[]	A vector of exception types which should count as failures
:ignore-exceptions	[]	A vector of exception types which should not count as failures
:record-failure	(constantly true)	A predicate that receives an exception and determines whether it should count as a failure

A config can be used to configure the global registry or a single circuit breaker when it is created.

Global Registry

This library creates a single global registry The registry may contain config values as well as circuit breaker instances.

configure-registry! overwrites the existing registry with one containing one or more config values. configure-registry! takes a map of name/config value pairs. When a circuit breaker is created, it may refer to one of these names to use the associated config. Note that the name :default (or "default") is special in that circuit breakers that are created without a providing or naming a config with use this default config.

The function circuit-breaker! will look up or create a circuit breaker in the global registry. The function accepts a name and optionally the name of a config or a config map.

(ns myproject.core
  (:require [resilience4clj.circuit-breaker :as cb])

;; The following creates two configs: the default config and the FailFaster
;; config. The default config uses only the defaults and will be used to create
;; circuit breakers that do not specify a config to use.
(cb/configure-registry! {"default"    {}
                         "FailFaster" {:failure-rate-threshold 20}})


;; create a circuit breaker named :name using the "default" config from the
;; registry and store the result in the registry
(cb/circuit-breaker! :name)

;; create a circuit breaker named :fail-faster using the "FailFaster" config
;; from the registry and store the result in the registry
(cb/circuit-breaker! :fail-faster "FailFaster")

;; create a circuit breaker named :custom-config using a custom config map
;; and store the result in the registry
(cb/circuit-breaker! :custom-config {:ring-buffer-size-in-closed-state 10})

Custom Circuit Breakers

While convenient, it is not required to use the global registry. You may instead choose to create circuit breakers and manage them yourself.

In order to create a circuit breaker that is not made available globally, use the circuit-breaker function, which accepts a name and config map.

The following code creates a new circuit-breaker with the default config options.

(ns myproject.core
  (:require [resilience4clj.circuit-breaker :as cb]))

(def my-breaker (cb/circuit-breaker :my-breaker {}))