Elastic Whenever

Manage ECS scheduled tasks like Whenever gem.

Installation

Add this line to your application's Gemfile:

gem 'elastic_whenever'

And then execute:

$ bundle

Or install it yourself as:

$ gem install elastic_whenever

Usage

You can use it almost like Whenever. However, please be aware that you must specify an identifier.

$ elastic_whenever --help
Usage: elastic_whenever [options]
    -i, --update identifier          Clear and create scheduled tasks by schedule file
    -c, --clear identifier           Clear scheduled tasks
    -l, --list identifier            List scheduled tasks
    -s, --set variables              Example: --set 'environment=staging'
        --cluster cluster            ECS cluster to run tasks
        --task-definition task_definition
                                     Task definition name, If omit a revision, use the latest revision of the family automatically. Example: --task-deifinition oneoff-application:2
        --container container        Container name defined in the task definition
        --launch-type launch_type    Launch type. EC2 or FARGATE. Defualt: EC2
        --assign-public-ip           Assign a public IP. Default: DISABLED (FARGATE only)
        --security-groups groups     Example: --security-groups 'sg-2c503655,sg-72f0cb0a' (FARGATE only)
        --subnets subnets            Example: --subnets 'subnet-4973d63f,subnet-45827d1d' (FARGATE only)
        --platform-version version   Optionally specify the platform version. Default: LATEST (FARGATE only)
    -f, --file schedule_file         Default: config/schedule.rb
        --iam-role name              IAM role name used by CloudWatch Events. Default: ecsEventsRole
        --rule-state state           The state of the CloudWatch Events Rule (ENABLED or DISABLED), default: ENABLED
        --profile profile_name       AWS shared profile name
        --access-key aws_access_key_id
                                     AWS access key ID
        --secret-key aws_secret_access_key
                                     AWS secret access key
        --region region              AWS region
    -v, --version                    Print version
    -V, --verbose                    Run rake jobs without --silent

NOTE: Currently, Elastic Whenever supports the Whenever syntax partially. We strongly encourage to use dry-run mode for verifying tasks to be created.

$ elastic_whenever --cluster ecs-test --task-definition example:2 --container cron
cron(0 3 * * ? *) ecs-test example:2 cron bundle exec rake hoge:run

## [message] Above is your schedule file converted to scheduled tasks; your scheduled tasks was not updated.
## [message] Run `elastic_whenever --help' for more options.

Setting variables

Elastic Whenever supports setting variables via the --set option as Whenever does.

Example:

elastic_whenever --set 'environment=staging&some_var=foo'

if @environment == 'staging'
  every '0 1 * * *' do
    rake 'some_task_on_staging'
  end
elsif @some_var == 'foo'
  every '0 10 * * *' do
    rake 'some_task'
  end
end

Especially, @environment defaults to "production".

How it works

Elastic Whenever creates CloudWatch Events for every command. Each rule has a one to one mapping to a target. for example, the following input will generate two Rules each with one Target.

every '0 0 * * *' do
  rake "hoge:run"
  command "awesome"
end

The scheduled task's name is a digest value calculated from an identifier, commands, and so on.

NOTE: You should not use the same identifier across different clusters because CloudWatch Events rule names are unique across all clusters.

Compatibility with Whenever

job_type

Whenever supports custom job type with job_type method, but Elastic Whenever doesn't support it.

# [warn] Skipping unsupported method: job_type
job_type :awesome, '/usr/local/bin/awesome :task :fun_level'

env

Whenever supports environment variables with env method, but Elastic Whenever doesn't support it. You should use task definitions to set environment variables.

# [warn] Skipping unsupported method: env
env "VERSION", "v1"

:job_template

Whenever has a template to describe as cron, but Elastic Whenever doesn't have the template. Therefore, :job_template option is ignored.

set :job_template, "/bin/zsh -l -c ':job'" # ignored

Frequency

Elastic Whenever processes frequency passed to every block almost like Whenever.

# Whenever
#   0 15 * * * /bin/bash -l -c 'cd /home/user/app && RAILS_ENV=production bundle exec rake hoge:run --silent'
#
# Elastic Whenever
#   cron(0 15 * * ? *) ecs-test myapp:2 web bundle exec rake hoge:run --silent
#
every :day, at: "3:00" do
  rake "hoge:run"
end

# Whenever
#   0,10,20,30,40,50 * * * * /bin/bash -l -c 'awesome'
#
# Elastic Whenever
#   cron(0,10,20,30,40,50 * * * ? *) ecs-test myapp:2 web awesome
#
every 10.minutes do
  command "awesome"
end

However, handling of the day of week is partially different because it follows scheduled expression.

# Whenever
#   0 0 * * 1 /bin/bash -l -c 'awesome'
#
# Elastic Whenever
#   cron(0 0 ? * 2 *) ecs-test myapp:2 web awesome
#
every :monday do
  command "awesome"
end

Therefore, cron syntax is converted to scheduled expression like the following:

# cron(0 0 ? * 2 *) ecs-test myapp:2 web awesome
every "0 0 * * 1" do
  command "awesome"
end

Absolutely, you can also write scheduled expression.

# cron(0 0 ? * 2 *) ecs-test myapp:2 web awesome
every "0 0 ? * 2 *" do
  command "awesome"
end

:reboot

Whenever supports :reboot as a cron option, but Elastic Whenever doesn't support it.

# [warn] `reboot` is not supported option. Ignore this task.
every :reboot do
  rake "hoge:run"
end

Bundle commands

Whenever checks if the application uses bundler and automatically adds a prefix to commands. However, Elastic Whenever always adds a prefix on a premise that the application is using bundler.

# Whenever
#   With bundler    -> bundle exec rake hoge:run
#   Without bundler -> rake hoge:run
#
# Elastic Whenever
#   bundle exec rake hoge:run
#
rake "hoge:run"

If you don't want to add the prefix, set bundle_command to empty as follows:

set :bundle_command, ""

Rails

Whenever supports runner job with old Rails versions, but Elastic Whenever supports Rails 4 and above only.

# Whenever
#   Before them -> script/runner Hoge.run
#   Rails 3     -> script/rails runner Hoge.run
#   Rails 4     -> bin/rails runner Hoge.run
#
# Elastic Whenever
#   bin/rails runner Hoge.run
#
runner "Hoge.run"

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec 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.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/wata727/elastic_whenever.