ServiceVariables

Service-wide Redis backed configuration variables which can be edited while your application is running. This is particularly useful for 12 factor apps which can scale arbitrarily but need centralized configuration. Data types, defaults and boundaries can all be specified.

Note: this was implemented on Redis 3.

Install

gem install service_variables

Usage

You will want to create a configuration object where you can configure the Redis endpoint and the define configuration variables.

require 'service_variables'

module App
  class Config
    extend ServiceVariables

    # redis_client [Required] Give the ServiceConfig object a Redis client to store values.
    # redis_key    [Optional] Specify a redis key if you have multiple of these
    #                         objects using the same Redis instance.
    # failure_mode [Optional] Sepcify a failure mode to fall back on if redis is unavailable.
    #                         Defaults to :raise_exception
    configure redis_client: Redis.new(url: ENV.fetch('REDIS_URL')),
              redis_key: 'special_key',
              failure_mode: :raise_exception

    boolean_option :foo, default: false, failure_mode: :use_last_value
    integer_option :bar, default: 10, min: 1, max: 100, failure_mode: :use_default
    float_option   :baz, default: 3.0, min: 1.0, max: 5.0
    string_option  :boo, default: 'fizz', enum: ['fizz', 'fuzz']

    # If the default param is not given, `nil` is assumed.
    # If boundary or enum params are not given, these checks are ignored.
  end
end

In your application you can then call or edit values.

App::Config.foo #=> false
App::Config.foo = true
App::Config.foo #=> true

App::Config.bar = 1_000 #=> throws InvalidValueError, 'Value too large. max = 1000'

Failure Modes

To protect against redis connection failures you can specify a designated failure mode when you create your configuration object or on a configuration variable granularity.

failure_mode: :raise_exception #=> raise an exception if cannot connect to Redis
failure_mode: :use_default #=> use the default value provided at configuration
failure_mode: :use_last_value #=> use the last value that was read from Redis

Testing

# spin up redis locally
docker run --rm -d -p 6379:6379 redis

# run spec
bundle exec rspec spec

Contributing

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

License

The gem is available open source under the terms of the Apache 2.0 License.