Fault Tolerant Capistrano

Imagine you have hundreds of hosts in Capistrano, and you'd like to allow specific command to fail on 5% of your hosts. The gem brings fault tolerant commands to Capistrano DSL:

on roles(:web), failure_tolerance: 0.05 do
  within release_path do
    execute "./script-that-may-fail-sometimes"
  end
end

Add this line to your application's Gemfile:

# it's important to set `require: false`
gem 'capistrano-fault-tolerant', require: false

You'll also need the edge version of SSHKit which includes the commit:

gem 'sshkit', github: 'capistrano/sshkit'

And then execute:

$ bundle

Add to Capfile:

require 'capistrano-fault-tolerant'

Now you can use failure_tolerance option with any command:

on roles(:web), failure_tolerance: 0.05 do
  within release_path do
    execute "./script-that-may-fail-sometimes"
  end
end

If > 5% of web hosts will fail, Capistrano will continue to deploy.

When < 5% of web hosts will fail, Capistrano will stop with an exception as it usually does with failed commands.

The gem can also call a callback on new failed host:

# config/deploy.rb
CapistranoFaultTolerant.on_failed_host = ->(host) {
  # notify someone about failed host
  puts "HOST FAILED: #{host}"
}

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/[USERNAME]/capistrano-fault-tolerant.

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