fix: Set the default DB adapter to sqlite3

Currently, if no DB adapter is set, both in stack JSON file, and application (no RDS resource
attached), the application crashes with `"There is no supported Db driver for given configuration."`
exception. This is not wanted behavior, as the main goal of this cookbook is to work in
zero-configuration environment. The fix resolves that problem, by simply setting the default DB
adapter to `sqlite3`.

README.md

@@ -78,8 +78,7 @@ for you.
 
 * `app['database']['adapter']`
   * **Supported values:** `mariadb`, `mysql`, `postgresql`, `sqlite3`
-  * **Note:** There is no default database adapter if a RDS resource is not
-    defined in your stack.
+  * **Default:** `sqlite3`
   * ActiveRecord adapter which will be used for database connection.
 * `app['database']['username']`
   * Username used to authenticate to the DB

attributes/default.rb

@@ -21,6 +21,11 @@
   nginx::http_stub_status_module
 )
 
+# database
+## common
+
+default['defaults']['database']['adapter'] = 'sqlite3'
+
 # scm
 ## common
 

libraries/drivers_db_base.rb

@@ -58,7 +58,8 @@ def app_engine
       end
 
       def node_engine
-        node['deploy'][app['shortname']]['database'].try(:[], 'adapter')
+        node['deploy'][app['shortname']]['database'].try(:[], 'adapter') ||
+          node['defaults'].try(:[], 'database').try(:[], 'adapter')
       end
 
       private

libraries/drivers_db_factory.rb

@@ -13,7 +13,8 @@ def self.detect_engine(app, node, options)
         Drivers::Db::Base.descendants.detect do |db_driver|
           db_driver.allowed_engines.include?(
             options.try(:[], :rds).try(:[], 'engine') ||
-            node.try(:[], 'deploy').try(:[], app['shortname']).try(:[], 'database').try(:[], 'adapter')
+            node.try(:[], 'deploy').try(:[], app['shortname']).try(:[], 'database').try(:[], 'adapter') ||
+            node.try(:[], 'defaults').try(:[], 'database').try(:[], 'adapter')
           )
         end
       end