DaemonRunner

This is a library that will assist you in writing long running services that are composed of discrete tasks. For example you may want to check that a service is running, or run some command and send it's output somewhere.

The basic design consists of a list of tasks that loop forever. The user is responsible to defining what those tasks are and what they do in a subclass.

Add this line to your application's Gemfile:

gem 'daemon_runner'

And then execute:

$ bundle

Or install it yourself as:

$ gem install daemon_runner

In order to use this gem you must subclass DaemonRunner::Client and add a few methods:

• tasks - This is an array of tasks to run (required)

[
  [ClassName1, method_name, args],
  [ClassName2, method_name, args]
]

• wait - Setup hook to run before starting tasks (optional)

• options - Options hash to pass to initialize (required)

  • :loop_sleep_time - Number of seconds to sleep before starting tasks again (optional, default: 5 seconds)
  • :error_sleep_time - Number of seconds to sleep before retying a failed task (optional, default: 5 seconds)
  • :post_task_sleep_time - Number of seconds to sleep after each task (optional, default: 1 seconds)

• schedule - How often the task should run. See Scheduling below. (optional)

#!/usr/bin/env ruby

require_relative '../lib/daemon_runner'

class MyService
  class Tasks
    class Foo
      def run!
        puts 'foo'
        'foo'
      end
    end
  end
end

class MyService
  class Tasks
    class Bar
      def run!(name)
        puts name
        name
      end
    end
  end
end

class MyService
  class Tasks
    class Baz
      class << self
        def run!(args)
          name = args[0]
          reason = args[1]
          puts name
          puts reason
          name
        end
      end
    end
  end
end

class MyService
  class Client < DaemonRunner::Client
    def tasks
      [
        [::MyService::Tasks::Foo.new, 'run!'],
        [::MyService::Tasks::Bar.new, 'run!', 'bar'],
        [::MyService::Tasks::Baz, 'run!', 'baz', 'because']
      ]
    end
  end
end

options = {}
service = MyService::Client.new(options)
service.start!

Tasks can define the schedule that they run on and how their schedule is executed. To do this, define a method named schedule with an array formatted as:

  [:schedule_type, duration]

For example, if you wanted your task to run every 5 minutes, you would do the following:

#!/usr/bin/env ruby

class MyService
  class Tasks
    class Quiz
      def schedule
        [:every, '5m']
      end

      def run!(args)
        puts args
        args
      end
    end
  end
end

This would execute the run! method every 5 minutes. Duration can be defined as a string in the '<number>s/m/h/d/w' format or as a number of seconds. Schedule types are :in, :at, :every, :cron, :interval. See rufus-scheduler's README for more information.

The default for tasks that don't explicitly define a schedule is

def schedule
  [:interval, options[:loop_sleep_time]]
end

Simple interface to retry requests that are known to fails sometimes. To add a retry wrap the code like this:

DaemonRunner::RetryErrors.retry do
  my_not_so_good_network_service_that_fails_sometimes
end

• options - Options hash to pass to retry (optional)
  • :retries - Number of times to retry an exception (optional, default: 3)
  • :exceptions - Array of exceptions to catch and retry (optional, default: [Faraday::ClientError])

Locking can be done either via an exclusive lock or a semaphore lock. The major difference is that with a semaphore lock you can define how many nodes can obtain the lock.

TBD

For an example of how to implement semaphore locking take a look at the manual locking example and the slightly more automatic version.

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/rapid7/daemon_runner. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

The gem is available as open source under the terms of the MIT License.