Change set on update (#178)

Use a ChangeSet for stack updates.

docs/user-guide/cli.md

@@ -139,12 +139,19 @@ ELB failures which will result in instance replacements.
 
 ## `moonshot update`
 
-Update an environment with the latest local CloudFormation template,
-and any Parameter updates specified via `--answer-file` or
-`--parameter`. If there are new parameters in the template and they
-are not specified, the user will be prompted for their values, unless
-`--no-interactive` is specified, in which case an error will be
-displayed.
+Update an environment with the latest local CloudFormation template
+using a ChangeSet. Keep all existing parameters, unless they are
+specified by `--answer-file` and/or `--parameter`. If there are new
+parameters in the template and they are not specified, the user will
+be prompted for their values, unless `--no-interactive` is specified,
+in which case an error will be displayed.
+
+The user is prompted interactively to accept the ChangeSet, unless
+`--no-interactive` is set. `--force` can be specified to automatically
+accept the changes. If `--dry-run` is set, the changes are
+automatically rejected after being displayed, which can be useful for
+seeing what the impact of a template change might be in a given
+environment.
 
 ### Options
 
@@ -164,6 +171,17 @@ See [create][#moonshot-create].
 
 See [create][#moonshot-create].
 
+#### `--force`
+
+Automatically accept the ChangeSet that was generated, without
+prompting the user. The changes are still displayed in the log
+output.
+
+#### `--dry-run`
+
+Automatically reject the ChangeSet that was generated, after
+displaying the changes.
+
 ### Examples
 
 Update a single Stack parameter, using the latest template:

lib/moonshot.rb

@@ -54,8 +54,6 @@ module Plugins
   'stack_config',
   'stack_lister',
   'stack_events_poller',
-  'merge_strategy',
-  'default_strategy',
   'ask_user_source',
   'always_use_default_source',
 

lib/moonshot/change_set.rb

@@ -0,0 +1,100 @@
+module Moonshot
+  class ChangeSet
+    attr_reader :name
+    attr_reader :stack_name
+
+    def initialize(name, stack_name)
+      @name = name
+      @stack_name = stack_name
+      @change_set = nil
+      @cf_client = Aws::CloudFormation::Client.new
+    end
+
+    def confirm?
+      unless Moonshot.config.interactive
+        raise 'Cannot confirm ChangeSet when interactive mode is disabled!'
+      end
+
+      loop do
+        print 'Apply changes? '
+        resp = gets.chomp.downcase
+
+        return true if resp == 'yes'
+        return false if resp == 'no'
+        puts "Please enter 'yes' or 'no'!"
+      end
+    end
+
+    def valid?
+      @change_set.status == 'CREATE_COMPLETE'
+    end
+
+    def invalid_reason
+      @change_set.status_reason
+    end
+
+    def display_changes
+      wait_for_change_set unless @change_set
+
+      @change_set.changes.map(&:resource_change).each do |c|
+        puts "* #{c.action} #{c.logical_resource_id} (#{c.resource_type})"
+
+        if c.replacement == 'True'
+          puts ' - Will be replaced'
+        elsif c.replacement == 'Conditional'
+          puts ' - May be replaced (Conditional)'
+        end
+
+        c.details.each do |d|
+          case d.change_source
+          when 'ResourceReference', 'ParameterReference'
+            puts " - Caused by #{d.causing_entity.blue} (#{d.change_source})"
+          when 'DirectModification'
+            puts " - Caused by template change (#{d.target.attribute}: #{d.target.name})"
+          end
+        end
+      end
+    end
+
+    def execute
+      wait_for_change_set unless @change_set
+      @cf_client.execute_change_set(
+        change_set_name: @name,
+        stack_name: @stack_name)
+    end
+
+    def delete
+      wait_for_change_set unless @change_set
+      @cf_client.delete_change_set(
+        change_set_name: @name,
+        stack_name: @stack_name)
+    rescue Aws::CloudFormation::Errors::InvalidChangeSetStatus
+      sleep 1
+      retry
+    end
+
+    # NOTE: At the time of this patch, AWS-SDK native Waiters do not
+    # have support for ChangeSets. Once they add this, we can make
+    # this code much better.
+    def wait_for_change_set
+      start = Time.now.to_i
+
+      loop do
+        resp = @cf_client.describe_change_set(
+          change_set_name: @name,
+          stack_name: @stack_name)
+
+        if %w(CREATE_COMPLETE FAILED).include?(resp.status)
+          @change_set = resp
+          return
+        end
+
+        if Time.now.to_i > start + 30
+          raise 'ChangeSet did not complete creation within 30 seconds!'
+        end
+
+        sleep 0.25 # http://bit.ly/1qY1ZXJ
+      end
+    end
+  end
+end

lib/moonshot/commands/update.rb

@@ -8,22 +8,22 @@ class Update < Moonshot::Command
       self.usage = 'update [options]'
       self.description = 'Update the CloudFormation stack within an environment.'
 
-      def execute
-        controller.update
-      end
+      def parser
+        parser = super
 
-      private
+        parser.on('--dry-run', TrueClass, 'Show the changes that would be applied, but do not execute them') do |v| # rubocop:disable LineLength
+          @dry_run = v
+        end
 
-      def parameter_strategy_factory(value)
-        case value.to_sym
-        when :default
-          Moonshot::ParameterStrategy::DefaultStrategy.new
-        when :merge
-          Moonshot::ParameterStrategy::MergeStrategy.new
-        else
-          raise "Unknown parameter strategy: #{value}"
+        parser.on('--force', '-f', TrueClass, 'Apply ChangeSet without confirmation') do |v|
+          @force = v
         end
       end
+
+      def execute
+        @force = true unless Moonshot.config.interactive
+        controller.update(dry_run: @dry_run, force: @force)
+      end
     end
   end
 end

lib/moonshot/controller.rb

@@ -71,7 +71,7 @@ def create # rubocop:disable AbcSize
       end
     end
 
-    def update # rubocop:disable AbcSize
+    def update(dry_run:, force:) # rubocop:disable AbcSize
       # Scan the template for all required parameters and configure
       # the ParameterCollection.
       @config.parameters = ParameterCollection.from_template(stack.template)
@@ -119,7 +119,7 @@ def update # rubocop:disable AbcSize
       end
 
       run_hook(:deploy, :pre_update)
-      stack.update
+      stack.update(dry_run: dry_run, force: force)
       run_hook(:deploy, :post_update)
       run_plugins(:post_update)
     end

lib/moonshot/controller_config.rb

@@ -1,4 +1,3 @@
-require_relative 'default_strategy'
 require_relative 'ssh_config'
 require_relative 'task'
 require_relative 'ask_user_source'