Knifeswitch

Yet another circuit breaker gem. This one strives to be as small and simple as possible. In the effort to remain simple, it currently only supports Rails with MySQL.

Usage

# Instantiate circuit
circuit = Knifeswitch::Circuit.new(
  namespace:       'whatever',
  exceptions:      [TimeoutExceptionToCatch, Timeout::Error],
  error_threshold: 5,
  error_timeout:   60
)

response = circuit.run { client.request(...) }
# 'run' will raise Knifeswitch::CircuitOpen if its error_threshold has
# been exceeded. In this case: when a timeout occurs 5 times in a row.
# 
# The error threshold counter is shared among all Knifeswitch::Circuit
# instances with the same namespace. The counters are stored in the db,
# so the state is fully distributed among all your workers/webservers.
#
# After the circuit opens, it will close back down after 60 seconds of
# rejecting requests (by raising Knifeswitch::CircuitOpen).
#
# When closed, it will just run the block like normal and return the result.

Installation

Add this line to your application's Gemfile:

gem 'knifeswitch'

And then execute:

$ bundle

Finally, generate migrations:

$ rake knifeswitch:create_migrations

Testing

Have Docker installed?

$ bin/dockertest

Manually, without docker

You'll need to set up the test Rails app's database. Edit test/dummy/config/database.yml as you see fit, and run:

$ rake knifeswitch:create_migrations db:create db:migrate

inside of the test/dummy directory.

After that you can run:

$ bin/test

in the project root with no problem. If you end up changing the migration generation rake task, you'll have to clean up and re-run it manually.

Limitations

To keep the gem simple, Knifeswitch depends on Rails. Technically, it should be pretty simple to make Knifeswitch work without the Rails dependency, but for us since we use Rails it's easier to just keep it as is.

Knifeswitch also softly depends on MySQL, in that it uses MySQL's ON DUPLICATE KEY UPDATE syntax.