ConsulApplicationSettings

This gem is deprecated and all functionality has been moved to SettingsReader See More: https://github.com/matic-insurance/settings_reader

This gem that simplifies usage of Consul (via Diplomat gem) to host application settings.

Except reading value from Consul the gem also:

• Fallbacks to YAML if value is missing in consul
• Resolve actual value from other sources to facilitate overriding via ENV, storing secret values in Vault,
  or executing small ERB snippets

Default values in YAML also can be considered as a way to communicate structure of settings to other engineers. Default values also support local settings to allow override on local environment or deployment in production.

Add this line to your application's Gemfile:

gem 'consul_application_settings'

At the load of application:

ConsulApplicationSettings.configure do |config|
  # Specify path to the base settings YML. Default: 'config/app_settings.yml' 
  config.base_file_path = Rails.root.join('config/app_settings.yml')
  # Specify path to the local settings YML, which overrides the base file. Default: 'config/app_settings.local.yml'
  config.local_file_path = Rails.root.join('config/app_settings.local.yml')
  # Specify whether exception should be thrown on Consul connection errors. Default: false
  config.disable_consul_connection_errors = true
  # Specify setting providers. Default: [ConsulApplicationSettings::Providers::ConsulPreloaded, ConsulApplicationSettings::Providers::LocalStorage]
  config.settings_providers = [
    ConsulApplicationSettings::Providers::Consul,          
    ConsulApplicationSettings::Providers::LocalStorage          
  ]
  # Specify how values will be additionally resolved. Default: [ConsulApplicationSettings::Resolvers::Env] 
  config.value_resolvers = [
    ConsulApplicationSettings::Resolvers::Erb,
    ConsulApplicationSettings::Resolvers::Env,
  ]
end

# Specify path to settings both in YML files and Consul
AUTH_SETTIGNS = ConsulApplicationSettings.load('my_cool_app')
# Load at root without any prefix: APP_SETTINGS = ConsulApplicationSettings.load

NOTE For rails you can add this code to custom initializer console_application_settings.rb in app/config/initializers

NOTE Diplomat gem should be configured before requesting any settings

Assuming your defaults file in repository config/application_settings.yml looks like:

my_cool_app:
  app_name: 'MyCoolApp'
  hostname: 'http://localhost:3001'
  
  integrations:
    database:
      domain: localhost
      user: app
      password: password1234
    slack:
      enabled: false
      webhook_url: 'https://hooks.slack.com/services/XXXXXX/XXXXX/XXXXXXX'

And consul has following settings

{
  "my_cool_app": {
   "hostname": "https://mycoolapp.com",
   "integrations": {
      "database": {
        "domain": "194.78.92.19",
        "password": "*************"
      },
      "slack": {
        "enabled": "true"
      }
    }
  }
}

Anywhere in your code base, after initialization, you can use previously loaded settings to query any key by full path

APP_SETTINGS['app_name']                           # "MyCoolApp"
APP_SETTINGS.get(:hostname)                     # "https://mycoolapp.com"

APP_SETTINGS.get('integrations/database/user')  # "app"
APP_SETTINGS['integrations/slack/enabled']      # true

Assuming some part of your code needs to work with smaller part of settings - gem provides interface to avoid duplicating absolute path

# You can load subsettings from root object
db_settings = APP_SETTINGS.load('integrations/database') # ConsulApplicationSettings::Reader
db_settings.get(:domain)                  # "194.78.92.19"
db_settings['user']                       # "app"

#if you try to get subsettings via get - error is raised
APP_SETTINGS.get('integrations/database') # raise ConsulApplicationSettings::Error

Providers controls how and in which order settings are retrieved. When application asks for specific setting - gem retrieves them from every provider in order of configuration until one returns not nil value.

Default order for providers is:

1. ConsulApplicationSettings::Providers::ConsulPreloaded
2. ConsulApplicationSettings::Providers::LocalStorage

List of built in providers:

• ConsulApplicationSettings::Providers::ConsulPreloaded - Retrieves all settings from consul on every .load
• ConsulApplicationSettings::Providers::Consul - Retrieves setting every time .get method is called
• ConsulApplicationSettings::Providers::LocalStorage - Retrieves all settings from local files on every .load

Custom provider can be added as long as it support following interface:

class CustomProvider
  #constructor
  def initialize(base_path, config)
  end
  
  # get value by `base_path + '/' + path`
  def get(path)
  end
end

Once value is retrieved - it will be additionally processed by resolvers. This allows for additional flexibility like getting values from external sources. While every resolver can be implemented in a form of a provider - one will be limited by the structure of settings, while other system might not be compatible with this.

When value is retrieved - gem finds first provider that can resolve value and resolves it. Resolved value is returned to application.

Default list of resolvers:

• ConsulApplicationSettings::Resolvers::Env

List of built in resolvers

• ConsulApplicationSettings::Resolvers::Env - resolves any value by looking up environment variable. Matching any value that starts with env://. Value like env://TEST_URL will be resolved as ENV['TEST_URL']
• ConsulApplicationSettings::Resolvers::Erb - resolves value by rendering it via ERB. Matching any value that contains <% and %> in it. Value like <%= 2 + 2 %> will be resolved as 4

You can configure gem with block:

ConsulApplicationSettings.configure do |config|
  config.local_file_path = 'config/config.yml'
end

or one option at a time

ConsulApplicationSettings.config.local_file_path = 'config/config.yml'

All Gem configurations

1. Run bin/setup to install dependencies
2. Run docker-compose up to spin up dependencies (Consul)
3. Run tests rspec
4. Add new test
5. Add new code
6. Go to step 3
7. Create PR

Bug reports and pull requests are welcome on GitHub at https://github.com/matic-insurance/consul_application_settings. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

The gem is available as open source under the terms of the MIT License.

Everyone interacting in the ConsulApplicationSettings project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.