Whenever::Elasticbeanstalk

Whenever-elasticbeanstalk is an extension gem to Whenever that automatically ensures that one instance in an AWS Elastic Beanstalk environment is set as leader. This allows you to run cron jobs on all instances, or just on the leader. This is required since Elastic Beanstalk may start or stop any instance as it scales up or down.

Installation

Add this line to your application's Gemfile:

gem 'whenever-elasticbeanstalk'

And then execute:

$ bundle

Or install it yourself as:

$ gem install whenever-elasticbeanstalk

Getting started

$ cd /apps/my-great-project
$ wheneverize-eb .

This will create an initial config/schedule.rb file for you with the ensure_leader job set to run every minute. It will also create a .ebextensions/cron.config file that will automatically choose a leader on environment initialization, and start up Whenever with the correct leader role. Lastly, it creates the config/whenever-elasticbeanstalk.yml file that will contain your AWS credentials for retrieving your environment information.

Manually updating schedule

If you are already using Whenever, running wheneverize-eb . won't overwrite your config/schedule.rb file. You'll need to add the following lines in order for your environment to always have one leader.

every 1.minute do
  command "cd /var/app/current && bundle exec ensure_one_cron_leader"
end

Create AWS IAM user

In order for the scripts to work, you need to supply AWS credentials for a user with access to EC2 instances and tags. It is recommended to create a new user with limited access.

Example policy:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": [
        "ec2:DescribeInstanceAttribute",
        "ec2:DescribeInstanceStatus",
        "ec2:DescribeInstances",
        "ec2:DescribeTags",
        "ec2:CreateTags"
      ],
      "Resource": [
        "*"
      ],
      "Effect": "Allow"
    }
  ]
}

Then add the credentials to your config/whenever-elasticbeanstalk.yml file.

staging:
    access_key_id: 'your access key'
    secret_access_key: 'your secret access key'

Make sure to add the RAILS_ENV environment variable to your environment if you haven't already done so. This variable is not created automatically by AWS. You can add the following line to your .elasticbeanstalk/optionsettings.appname-env file:

RAILS_ENV=staging

Usage

For config/schedule.rb usage, please see the documentation for the Whenever gem.

Run a task on only one instance

To run a task only on one instance, assign the task to the leader role.

every :day, :at => "12:30am", :roles => [:leader] do
    runner "MyModel.task_to_run_nightly_only_on_one_instance"
end

Run a task on all instances

To run a task on all instance, omit the roles option.

every 1.minute do
    command "touch /opt/elasticbeanstalk/support/.cron_check"
end

Contributing

Fork it
Create your feature branch (git checkout -b my-new-feature)
Commit your changes (git commit -am 'Add some feature')
Push to the branch (git push origin my-new-feature)
Create new Pull Request