# Chef Data Region ## Description Chef Data Region extends the `Chef::DSL::DataQuery` module's `data_bag_item` method with the ability to dynamically expand the data bag name in a configurable, environment-specific manner. ## Motivation This gem exists to address the following scenario: An organization maintains data in Chef data bag items. The data is deployed to several data center environments and is stored in data bags whose names reference the environments. The organization wants to write environment-agnostic recipes that access the data bags without explicitly referencing the data bags by their environment names. As a concrete example, imagine the organization maintains encrypted data for three deployment environments: development, staging, and production. It maintains this data in three data bags, one for each environment, with data for services named `gadget` and `widget` in items: | Environment | Bag | Item | |-------------+----------------+--------| | Development | secure-dev | gadget | | Development | secure-dev | widget | | Production | secure-prod | gadget | | Production | secure-prod | widget | | Staging | secure-staging | gadget | | Staging | secure-staging | widget | The items are encrypted with a key unique to that environment to maximize security. Now consider how a recipe would access these bags. When then recipe is running, it needs to know the data center environment in order to construct the bag name. The organization would most likely assign the enviroment name to a node attribute. In a naive implementation, each recipe would include logic that examined the attribute's value to determine which bag to load. This would obviously duplicate code. Imagine instead that the organization wants to reference the bag by the name `secure` and rely on an _abstraction_ to translate `secure` into the environment-specific bag name. This gem provides that abstraction. ## Features This gem overrides the `data_bag_item` method with configurable logic that dynamically decides which bag to load. It retains API compatibility with `Chef::DSL::DataQuery#data_bag_item`, so existing recipes that call `data_bag_item` work without modification. The gem imposes no constraints on data bag item structure. ## Configuration Assign the region name to a node attribute that varies by environment: node.default['local'][region'] = 'staging' Add the following configuration to Chef Client's `client.rb` file. * Require the gem: require 'chef/data_region' * Configure the gem with a hash that maps a bag name to an expansion pattern: Chef::DataRegion.add( 'secure', { attribute: %w(local region), pattern: 'secure-%<attribute>s' } ) ## Bag name expansion The gem expands bag names using Ruby's `format` method. _More pending..._