resque-retry

A Resque plugin. Requires Resque 1.8.0 & resque-scheduler

resque-retry provides retry, delay and exponential backoff support for resque jobs.

Features

• Redis backed retry count/limit.
• Retry on all or specific exceptions.
• Exponential backoff (varying the delay between retrys).
• Small & Extendable - plenty of places to override retry logic/settings.

Usage / Examples

Just extend your module/class with this module, and your ready to retry!

Customisation is pretty easy, the below examples should give you some ideas =), adapt for your own usage and feel free to pick and mix!

Retry

Retry the job once on failure, with zero delay.

require 'require-retry'

class DeliverWebHook
  extend Resque::Plugins::Retry
  @queue = :web_hooks

  def self.perform(url, hook_id, hmac_key)
    heavy_lifting
  end
end

When a job runs, the number of retry attempts is checked and incremented in Redis. If your job fails, the number of retry attempts is used to determine if we can requeue the job for another go.

Custom Retry

class DeliverWebHook
  extend Resque::Plugins::Retry
  @queue = :web_hooks

  @retry_limit = 10
  @retry_delay = 120

  def self.perform(url, hook_id, hmac_key)
    heavy_lifting
  end
end

The above modification will allow your job to retry upto 10 times, with a delay of 120 seconds, or 2 minutes between retry attempts.

Alternatively you could override the retry_delay method to do something more special.

Exponential Backoff

Use this if you wish to vary the delay between retry attempts:

class DeliverSMS
  extend Resque::Plugins::ExponentialBackoff
  @queue = :mt_messages

  def self.perform(mt_id, mobile_number, message)
    heavy_lifting
  end
end

Default Settings

key: m = minutes, h = hours

              no delay, 1m, 10m,   1h,    3h,    6h
@backoff_strategy = [0, 60, 600, 3600, 10800, 21600]

The first delay will be 0 seconds, the 2nd will be 60 seconds, etc... Again, tweak to your own needs.

The number if retrys is equal to the size of the backoff_strategy array, unless you set retry_limit yourself.

Retry Specific Exceptions

The default will allow a retry for any type of exception. You may change it so only specific exceptions are retried using retry_exceptions:

class DeliverSMS
  extend Resque::Plugins::Retry
  @queue = :mt_messages

  @retry_exceptions = [NetworkError]

  def self.perform(mt_id, mobile_number, message)
    heavy_lifting
  end
end

The above modification will only retry if a NetworkError (or subclass) exception is thrown.

Customise & Extend

Please take a look at the yardoc/code for more details on methods you may wish to override.

Some things worth noting:

Job Identifier/Key

The retry attempt is incremented and stored in a Redis key. The key is built using the identifier. If you have a lot of arguments or really long ones, you should consider overriding identifier to define a more precise or loose custom identifier.

The default identifier is just your job arguments joined with a dash -.

By default the key uses this format: resque-retry:<job class name>:<identifier>.

Or you can define the entire key by overriding redis_retry_key.

class DeliverSMS
  extend Resque::Plugins::Retry
  @queue = :mt_messages

  def self.identifier(mt_id, mobile_number, message)
    "#{mobile_number}:#{mt_id}"
  end

  self.perform(mt_id, mobile_number, message)
    heavy_lifting
  end
end

Retry Arguments

You may override args_for_retry, which is passed the current job arguments, to modify the arguments for the next retry attempt.

class DeliverViaSMSC
  extend Resque::Plugins::Retry
  @queue = :mt_smsc_messages

  # retry using the emergency SMSC.
  def self.args_for_retry(smsc_id, mt_message)
    [999, mt_message]
  end

  self.perform(smsc_id, mt_message)
    heavy_lifting
  end
end

Install

$ gem install resque-retry