What's the best way to manage real-time configuration variables with Ruby on Rails?
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12-09-2019 - |
Question
I'm aware of YAML and plugins like rails-settings, but neither of these is useful for configuration settings that need to be changed in real time.
For instance, say I have MAX_ALLOWED_REGISTERED_USERS set at 2000, but I want to up it to 2300. With a typical "configuration" or YAML solution, this would involve changing a config file and redeploying. I'd prefer a database-backed RESTful approach where I could just change a key/value pair.
Thoughts?
Solution
I use a Configuration model similar to this:
# == Schema Information
# Schema version: 20081015233653
#
# Table name: configurations
#
# id :integer not null, primary key
# name :string(20) not null
# value :string(255)
# description :text
#
class InvalidConfigurationSym < StandardError; end
class Configuration < ActiveRecord::Base
TRUE = "t"
FALSE = "f"
validates_presence_of :name
validates_uniqueness_of :name
validates_length_of :name, :within => 3..20
# Enable hash-like access to table for ease of use.
# Raises InvalidConfigurationSym when key isn't found.
# Example:
# Configuration[:max_age] => 80
def self.[](key)
rec = self.find_by_name(key.to_s)
if rec.nil?
raise InvalidConfigurationSym, key.to_s
end
rec.value
end
# Override self.method_missing to allow
# instance attribute type access to Configuration
# table. This helps with forms.
def self.method_missing(method, *args)
unless method.to_s.include?('find') # skip AR find methods
value = self[method]
return value unless value.nil?
end
super(method, args)
end
end
Here's how I use it:
class Customer < ActiveRecord::Base
validate :customer_is_old_enough?
def customer_is_old_enough?
min_age = Date.today << (Configuration[:min_age].to_i * 12)
self.errors.add(:dob, "is not old enough") unless self.dob < min_age
end
end
One thing I'm not quite happy with is having to call #to_i
like in the sample, but since it works for me so far, I haven't put too much thought in redesigning it.
OTHER TIPS
Moneta may suit your needs, it is a key/value storage system with configurable backends:
http://yehudakatz.com/2009/02/12/initial-release-of-moneta-unified-keyvalue-store-api/
If you're running a multi-server application, mutable configuration needs to be stored centrally (unless you don't mind different servers having different configurations)
As posted above, Moneta is a decent choice, though I'd wager mecached is more widely-deployed alongside Rails applications.
Here's a naive suggestion: make a DB table, migration and ActiveRecord-model and treat your config like any other entity in the database, minus a controller and view. Just a thought.
Perhaps put this data in memcached, and have it expire frequently enough if you are too worried about disturbing the database.