breaker_box

Circuit breakers in ruby

Usage

Persistence Factories

There are two persistence factories to choose from. In-memory storage and redis storage. To use one or the other you just need to include them:

include 'breakerbox/persistence_factories/memory'
include 'breakerbox/persistence_factories/redis'

You can also create your own. Here is the memory factory as a simple example:

class PersistenceFactory
  @storage = {}

  def self.storage_for(name)
    @storage[name] ||= BreakerBox::Storage::Memory.new
  end

  def self.reset!
    @storage = {}
  end
end

BreakerBox.persistence_factory = PersistenceFactory

The classes that storage_for returns must conform to the persistence interface. Specifically, the classes will need these methods:

• fail!: Called when a breaker task fails
• clear!: Clears all previous failures
• all_since: Returns an array of failures that happen after a timestamp
• last_failure_time: returns the last time a failure occured on this breaker

Please looks in BreakerBox::MemoryStorage for an example implmentation.

BreakerBoxes

To use a breaker box, call BreakerBox.circuit_for(name). This will return a breaker that can wrap a task. Call your task with the breaker box like so:

  breaker = BreakerBox.circuit_for(:testing)
  breaker.run SendEmail

Failure Callbacks

If a task fails and you want some action, you can assign a failure callback to a breaker:

  breaker = BreakerBox.circuit_for(:testing)
  breaker.failure_callback = lambda { |e| Logger.alert('Email failed to send!') }
  breaker.run SendEmail

If you don't provide a failure callback, any exceptions raised by the task will be rethrown.

Breaker options

Breakers have the following default options:

• They trip by default after two failures within two minutes
• They retry after one hour

You can change these options by passing them into the breaker:

  breaker.options = {:failure_threshold_count => 10, :failure_threshold_time => 240, :retry_after => 60 * 60 * 2}

Tasks

Tasks are objects that do work and are passed into a breaker's run method. This object must have a .call method on it (so it could be a lambda or proc). If it fails, it should raise an exception.