The are multiple ways of configuring your Rails application for different
environments (e.g. staging, production, etc). One of the popular ones is
through environment variables. For example Heroku uses this type of
One of the benefits of it is that configuration values are never stored in the
source control system, which improves security (for sensitive configuration
parameters) and also makes it easier to try different configuration setups w/o
changing the sources or re-deploying the application.
On the other hand writing (ENV['PRIMARY_DOMAIN'] || "myapp.com") every time
you need your domain string becomes cumbersome pretty fast, not to mention
duplication and having the default repeated all over the place.
A competent programmer will of course only do this once, and re-use the value
everywhere. Something like this:
PRIMARY_DOMAIN = ENV['PRIMARY_DOMAIN'].presence || 'myapp.com'
S3_BUCKET = ENV['S3_BUCKET'] || raise 'missing S3_BUCKET'
ORDER_EXPIRATION_DAYS = (ENV['ORDER_EXPIRATION_DAYS'].presence || 1).to_i
But it quickly becomes complicated, and again, quite a bit of similarly looking
code that begs to be refactored out.
constfig is something I extracted from a
couple of my latest projects. It allows you to do just that, have a
configuration parameters stored in constants with values coming from
environment variables and ability to provide defaults or have required
parameters (i.e. fail if missing).
I just released version 0.0.1 of constfig
to rubygems. Sources are of course on
Add this line to your application's Gemfile:
And then execute:
Or install it yourself as:
There is only one function provided by the gem: define_config.
With a default (optional variable)
You can call it with a default, like this:
define_config :DEFAULT_DOMAIN, "astrails.com"
In which case it will first look if ENV['DEFAULT_DOMAIN'] is available, and
if not will use the 'astrails.com'. A constant DEFAULT_DOMAIN will be
Without a default (required variable)
Or you can call it without the default:
In which case it will raise exception Constfig::Undefined if
ENV['DEFAULT_DOMAIN'] is not available.
One last thing. Non-string variables are supported. If you provide a non-string
default (boolean, integer, float or symbol), the value that is coming from
ENV will be converted to the same type (using to_i, to_f, and
to_symbol). For the true/false types "true", "TRUE", and "1" will be
treated as true, anything else will be treated as false.
In the case of required variables, you can supply a Class in place of the
default, and it will be used for the type conversion. Like this:
define_config :EXPIRATION_DAYS, Fixnum
For boolean variables you can supply either TrueClass, or FalseClass.
This gem will not re-define existing constants, which can be used to define
defaults for non-production environments.
Rails on Heroku
There is one caveat with Rails on Heroku. By default Heroku doesn't provide
environment variables to your application during the rake assets:precompile
stage of slug compilation. If you don't take care of it your application will
fail to compile its assets and might fail to work in production. To take care
of it you can either use Heroku Labs
option, or (and this is what I'd recommend) you can use development defaults
For example in Rails you con do this:
if Rails.env.development? || Rails.env.test? || ARGV.join =~ /assets:precompile/
DEFAULT_DOMAIN = 'myapp.dev'
In development and test environments it will use 'myapp.dev' ad
PRIMARY_DOMAIN, but in production and staging environment it will fail unless
PRIMARY_DOMAIN is provided by environment.
NOTE: make sure those configuration variables are not actually used for asset
compilation. If they are, I'd go with user-env-compile.
You can use the dotenv gem to manage your ENV.