Dynalock

Dynalock is a distributed lock that uses DynamoDB.

At Tourlane we were running cronjobs through Amazon ECS. Once the cluster became too big, CloudWatch was scheduling tasks, even if the same task was already present. Dynalock solves this issue, ensuring that any new task exits and fails before starting the real work.

The first assumption is that something like this should exist, but normally not as a command line program (if you found any, please let us know). So we created our own.

Add this line to your application's Gemfile:

gem 'dynalock'

And then execute:

$ bundle

Or install it yourself as:

$ gem install dynalock

You need to create a table in DynamoDB with "id" as a primary key, and "expires" as expires. The default table name is "locks".

Set the following environment variables to their proper values:

AWS_ACCESS_KEY_ID
AWS_REGION
AWS_SECRET_ACCESS_KEY

require 'dynalock'

include Dynalock::Lock

acquire_lock(context: "my_lock", table: TABLE, owner: @owner, expire_time: 10)
refresh_lock(context: "my_lock", table: TABLE, owner: @owner, expire_time: 10)
with_lock(context: "my_lock", table: TABLE, owner: @owner) { "Only run this" }

Most of the paramenters are optional

acquire_lock(context: "my_lock")
refresh_lock(context: "my_lock")
with_lock(context: "my_lock") { "Only run this" }

$ dynalock my_program

This will try to acquire a lock in DynamoDB for 10 seconds, and refresh it every 5 seconds and run your program. The command will be context.

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.

By default, the test suite will try to connect to AWS DynamoDB.

To work locally instead, you can use the local version of DynamoDB via Docker:

docker run -p 8000:8000 amazon/dynamodb-local

Then instruct the test suite to create the table & target that local instance:

DYNAMODB_CREATE_TEST_TABLE=1 DYNAMODB_ENDPOINT=http://localhost:8000 bundle exec rake

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

Everyone interacting in the Dynalock project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.