CConfig

CConfig (Container Config) is a container-aware configuration management gem. This is useful for applications that want to keep a reference configuration and add modifications to it in two different ways:

An alternative configuration file that lists all the modifications.
A list of environment variables that follow a given naming policy.

Basic usage

Let's assume that our application has a config.yml file that contains all the possible configurable values with their defaults:

option:
  enabled: true

another:
  value: 5

Then, you will have the following (irb prompt):

>> require "cconfig/cconfig"
>> cfg = ::CConfig::Config.new(default: "config.yml", local: "", prefix: "")
>> obj = cfg.fetch
>> puts obj
=> {"option"=>{"enabled"=>true}, "another"=>{"value"=>5}}

Moreover, this gem also adds an enabled? method to this hash returned by #fetch. With this method, configurable values with an enabled boolean value will have this shorthand available. For example:

>> obj.enabled?("option")
=> true
>> obj.enabled?("another")
=> false

This also works for embedded configurable options. From the above example, let's assume that we update the config.yml file with these contents:

option:
  enabled: true

  embedded:
    enabled: false

another:
  value: 5

Let's also add an alternative configuration file with these contents:

option:
  embedded:
    enabled: true

Then we have the following:

>> cfg = ::CConfig::Config.new(default: "config.yml", local: "config-local.yml", prefix: "")
>> obj = cfg.fetch
=> {"option"=>{"enabled"=>true, "embedded"=>{"enabled"=>true}}, "another"=>{"value"=>5}}
>> obj.enabled?("option.embedded")
=> true

As you can see, the contents from the config-local.yml file that are available in the config.yml have been overwritten.

That being said, mounting a volume for changing some default values inside of a Docker container is a bit of an overkill. So, instead you can use environment variables. In the above example we can add an environment variable (shell prompt):

$ export APPLICATION_ANOTHER_VALUE=2

Then (irb prompt):

>> cfg = ::CConfig::Config.new(default: "config.yml", local: "config-local.yml", prefix: "application")
>> cfg.fetch
=> {"option"=>{"enabled"=>true, "embedded"=>{"enabled"=>true}}, "another"=>{"value"=>2}}

Moreover, the environment variable value takes precedence over the config-local.yml file.

Ruby on Rails integration

This gem also provides a Railtie, so it can be better used inside of a Ruby on Rails application.

First of all, this Railtie will initialize a global constant named APP_CONFIG automatically with the merged contents of the configuration files and environment variables. Some notes:

The prefix is taken from the Rails' application name. If you don't want this, set the CCONFIG_PREFIX environment variable.
The file with the default values has to be located in config/config.yml from your Ruby on Rails root directory. Moreover, the other file is located in config/config-local.yml, but this can be changed by setting the #{prefix}_LOCAL_CONFIG_PATH environment variable.

Last but not least, this Railtie also offers a rake task called cconfig:info. This rake task prints to standard output the evaluated configuration.

License

This project is based on work I did for the Portus project. I've extracted my code into a gem so it can be also used for other projects that might be interested in this.

Copyright (C) 2017 Miquel Sabaté Solà <[email protected]>

CConfig is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

CConfig is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU Lesser General Public License
along with CConfig.  If not, see <http://www.gnu.org/licenses/>.