Allow setting of AutoRollback instance refresh preference (#10)

* Allow setting of `AutoRollback` instance refresh preference

* Update context name

README.md

@@ -106,6 +106,12 @@ set :asg_wait_for_instance_refresh, true
 set :asg_instance_refresh_polling_interval, 30 # default
 ```
 
+Enable or disable auto-rollback on instance refreshes (default: false):
+
+```ruby
+# config/deploy.rb 
+set :asg_instance_refresh_auto_rollback, true
+
 ## Usage
 
 Specify the Auto Scaling Groups with the keyword `autoscale` instead of using the `server` keyword in Capistrano's stage configuration. Provide the name of the Auto Scaling Group and any properties you want to pass to the server:

lib/capistrano/asg/rolling/autoscale_group.rb

@@ -55,6 +55,10 @@ def min_healthy_percentage
           properties.fetch(:min_healthy_percentage, nil)
         end
 
+        def auto_rollback
+          properties.fetch(:asg_instance_refresh_auto_rollback, nil)
+        end
+
         def max_healthy_percentage
           properties.fetch(:max_healthy_percentage, nil)
         end
@@ -73,7 +77,8 @@ def start_instance_refresh(launch_template)
               instance_warmup: instance_warmup_time,
               skip_matching: true,
               min_healthy_percentage: min_healthy_percentage,
-              max_healthy_percentage: max_healthy_percentage
+              max_healthy_percentage: max_healthy_percentage,
+              auto_rollback: auto_rollback
             }.compact
           ).instance_refresh_id
         rescue Aws::AutoScaling::Errors::InstanceRefreshInProgress => e

spec/capistrano/asg/rolling/autoscale_group_spec.rb

@@ -85,6 +85,22 @@
     end
   end
 
+  describe '#auto_rollback' do
+    subject(:group) { described_class.new('test-asg', asg_instance_refresh_auto_rollback: false) }
+
+    it 'returns the value set in the configuration' do
+      expect(group.auto_rollback).to be false
+    end
+
+    context 'when no value is set' do
+      subject(:group) { described_class.new('test-asg', {}) }
+
+      it 'returns `nil`' do
+        expect(group.auto_rollback).to be_nil
+      end
+    end
+  end
+
   describe '#min_healthy_percentage' do
     context 'when no value is set' do
       it 'returns nil' do