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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.

This gem supports Ruby on Rails 5.x, 6.x and 7.x.

Contributing

Read the CONTRIBUTING.md file.

Changelog

Read the CHANGELOG.md file.

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) 2017-2022 Miquel Sabat