Crowsnest

Introduction

Service discovery can be a challenge. Often the technique used in development will not be the one used on production. The methods used on Heroku may be different than the ones used on EC2.

Crowsnest is a Ruby library which sits on top of a number of different client libraries to provide service discovery. Ideally, one would use something like Zookeeper, but for testing, something like Moneta can be used instead.

Installation

gem install crowsnest

Usage

Environment variables

Set some of the following environment variables:

# For the "Env" adapter:
CROWSNEST_ENV_WEB='some.host;some.other.host'

# For the "Heroku" adapter:
HEROKU_API_KEY='1234'
HEROKU_APP_NAME='falling-water-255'

# For the "Moneta" adapter:
MONETA_URL='moneta://Memory?prefix=registrations%3A'

# For the "Zookeeper" adapter:
ZOOKEEPER_URL='localhost:2181'
ZOOKEEPER_PREFIX='/registrations'

# For the "Redis" adapter:
REDIS_URL='redis://localhost:6379'
REDIS_PREFIX='registrations'

Then from your Ruby code:

require 'crowsnest'

# Fetch some adapter based on environment variables set above.
adapter = Crowsnest.create

# Register this service.
adapter.register('web')
# You can also choose a key manually.
adapter.register('web', 'foo')

# If the process exits, try to deregister gracefully.
at_exit do
  adapter.deregister('web')
end

# If necessary, notify the discovery service periodically.
if adapter.heartbeat?
  Thread.new do
    loop do
      adapter.heartbeat('web')
      # Or...
      adapter.heartbeat('web', 'foo')

      sleep 5
    end
  end
end

# If you'd like to see what services are available:
adapter.list('web') #=> ['some.host']

Options

Set some of the following options:

# For the "Env" adapter:
options = nil

# For the "Heroku" adapter:
options = {
  heroku_api_key: '1234',
  heroku_app_name: 'falling-water-255'
}

# For the "Moneta" adapter:
options = {
  moneta_url: 'moneta://Memory?prefix=registrations%3A'
}

# For the "Zookeeper" adapter:
options = {
  zookeeper_url: 'localhost:2181',
  zookeeper_prefix: '/registrations'
}

# For the "Redis" adapter:
options = {
  redis_url: 'redis://localhost:6379',
  redis_prefix: 'registrations'
}

Then you can instantiate it like so:

require 'crowsnest'

adapter = Crowsnest.create(options)

Caveats

TODO: Fill this out

TODO

Fill out caveats.
Test prefixes for Redis and Zookeeper.
Show how to instantiate an adapter directly.

rjungemann / crowsnest