Add --yes-param option for single-param update auto-confim on apply

lib/stack_master/cli.rb

@@ -42,6 +42,7 @@ def execute!
         c.description = "Creates or updates a stack. Shows a diff of the proposed stack's template and parameters. Tails stack events until CloudFormation has completed."
         c.example 'update a stack named myapp-vpc in us-east-1', 'stack_master apply us-east-1 myapp-vpc'
         c.option '--on-failure ACTION', String, "Action to take on CREATE_FAILURE. Valid Values: [ DO_NOTHING | ROLLBACK | DELETE ]. Default: ROLLBACK\nNote: You cannot use this option with Serverless Application Model (SAM) templates."
+        c.option '--yes-param PARAM_NAME', String, "Auto-approve stack updates when only parameter PARAM_NAME changes"
         c.action do |args, options|
           options.defaults config: default_config_file
           execute_stacks_command(StackMaster::Commands::Apply, args, options)

lib/stack_master/commands/apply.rb

@@ -13,6 +13,7 @@ def initialize(config, stack_definition, options = Commander::Command::Options.n
         @from_time = Time.now
         @options = options
         @options.on_failure ||= nil
+        @options.yes_param ||= nil
       end
 
       def perform
@@ -59,7 +60,11 @@ def use_s3?
 
       def diff_stacks
         abort_if_review_in_progress
-        StackDiffer.new(proposed_stack, stack).output_diff
+        differ.output_diff
+      end
+
+      def differ
+        @differ ||= StackDiffer.new(proposed_stack, stack)
       end
 
       def create_or_update_stack
@@ -125,12 +130,20 @@ def update_stack
           halt!(@change_set.status_reason)
         end
 
+        if differ.single_param_update?(@options.yes_param)
+          StackMaster.stdout.puts("Auto-approving update to single parameter #{@options.yes_param}")
+        else
+          ask_update_confirmation!
+        end
         @change_set.display(StackMaster.stdout)
+        execute_change_set
+      end
+
+      def ask_update_confirmation!
         unless ask?("Apply change set (y/n)? ")
           ChangeSet.delete(@change_set.id)
           halt! "Stack update aborted"
         end
-        execute_change_set
       end
 
       def upload_files

lib/stack_master/stack_differ.rb

@@ -1,4 +1,5 @@
 require "diffy"
+require "hashdiff"
 
 module StackMaster
   class StackDiffer
@@ -72,6 +73,14 @@ def noecho_keys
       end
     end
 
+    def single_param_update?(param_name)
+      return false if param_name.blank? || @current_stack.blank? || body_different?
+      differences = HashDiff.diff(@current_stack.parameters_with_defaults, @proposed_stack.parameters_with_defaults)
+      return false if differences.count != 1
+      diff = differences[0]
+      diff[0] == "~" && diff[1] == param_name
+    end
+
     private
 
     def display_diff(thing, diff)

spec/stack_master/commands/apply_spec.rb

@@ -13,6 +13,7 @@
   let(:proposed_stack) { StackMaster::Stack.new(template_body: template_body, template_format: template_format, tags: { 'environment' => 'production' } , parameters: parameters, role_arn: role_arn, notification_arns: [notification_arn], stack_policy_body: stack_policy_body ) }
   let(:stack_policy_body) { '{}' }
   let(:change_set) { double(display: true, failed?: false, id: '1') }
+  let(:differ) { instance_double(StackMaster::StackDiffer, output_diff: nil, single_param_update?: false) }
 
   before do
     allow(StackMaster::Stack).to receive(:find).with(region, stack_name).and_return(stack)
@@ -21,7 +22,7 @@
     allow(Aws::CloudFormation::Client).to receive(:new).and_return(cf)
     allow(Aws::S3::Client).to receive(:new).and_return(s3)
     allow(cf).to receive(:create_stack)
-    allow(StackMaster::StackDiffer).to receive(:new).with(proposed_stack, stack).and_return double.as_null_object
+    allow(StackMaster::StackDiffer).to receive(:new).with(proposed_stack, stack).and_return(differ)
     allow(StackMaster::StackEvents::Streamer).to receive(:stream)
     allow(StackMaster).to receive(:interactive?).and_return(false)
     allow(cf).to receive(:create_change_set).and_return(OpenStruct.new(id: '1'))
@@ -135,6 +136,21 @@ def apply
         expect(StackMaster::ChangeSet).to_not have_received(:execute).with(change_set.id)
       end
     end
+
+    context 'yes_param option is set' do
+      let(:yes_param) { 'YesParam' }
+      let(:options) { double(yes_param: yes_param).as_null_object }
+
+      before do
+        allow(StackMaster).to receive(:non_interactive_answer).and_return('n')
+        allow(differ).to receive(:single_param_update?).with(yes_param).and_return(true)
+      end
+
+      it "skips asking for confirmation on single param updates" do
+        expect(StackMaster::ChangeSet).to receive(:execute).with(change_set.id, stack_name)
+        StackMaster::Commands::Apply.perform(config, stack_definition, options)
+      end
+    end
   end
 
   context 'the stack does not exist' do

spec/stack_master/stack_differ_spec.rb

@@ -1,17 +1,19 @@
 RSpec.describe StackMaster::StackDiffer do
   subject(:differ) { described_class.new(proposed_stack, stack) }
+  let(:current_body) { '{}' }
+  let(:proposed_body) { "{\"a\": 1}" }
   let(:current_params) { Hash.new }
   let(:proposed_params) { { 'param1' => 'hello'} }
   let(:stack) { StackMaster::Stack.new(stack_name: stack_name,
                                        region: region,
                                        stack_id: 123,
-                                       template_body: '{}',
+                                       template_body: current_body,
                                        template_format: :json,
                                        parameters: current_params) }
   let(:proposed_stack) { StackMaster::Stack.new(stack_name: stack_name,
                                                 region: region,
                                                 parameters: proposed_params,
-                                                template_body: "{\"a\": 1}",
+                                                template_body: proposed_body,
                                                 template_format: :json) }
   let(:stack_name) { 'myapp-vpc' }
   let(:region) { 'us-east-1' }
@@ -43,4 +45,50 @@
       end
     end
   end
+
+  describe "#single_param_update?" do
+    let(:yes_param) { 'YesParam' }
+    let(:old_value) { 'old' }
+    let(:new_value) { 'new' }
+    let(:current_params) { { yes_param => old_value } }
+    let(:proposed_params) { { yes_param => new_value } }
+    let(:current_body) { proposed_body }
+
+    subject(:result) { differ.single_param_update?(yes_param) }
+
+    context "when only param changes" do
+      it { is_expected.to be_truthy }
+    end
+
+    context "when new stack" do
+      let(:stack) { nil }
+      it { is_expected.to be_falsey }
+    end
+
+    context "when no changes" do
+      let(:current_params) { proposed_params }
+      it { is_expected.to be_falsey }
+    end
+
+    context "when body changes" do
+      let(:current_body) { '{}' }
+      it { is_expected.to be_falsey }
+    end
+
+    context "on param removal" do
+      let(:proposed_params) { {} }
+      it { is_expected.to be_falsey }
+    end
+
+    context "on param first addition" do
+      let(:current_params) { {} }
+      it { is_expected.to be_falsey }
+    end
+
+    context "when another param also changes" do
+      let(:current_params) { { yes_param => old_value, 'other' => 'old' } }
+      let(:proposed_params) { { yes_param => new_value, 'other' => 'new' } }
+      it { is_expected.to be_falsey }
+    end
+  end
 end

stack_master.gemspec

@@ -56,6 +56,7 @@ Gem::Specification.new do |spec|
   spec.add_dependency "deep_merge"
   spec.add_dependency "cfndsl"
   spec.add_dependency "multi_json"
+  spec.add_dependency "hashdiff"
   spec.add_dependency "dotgpg" unless windows_build
   spec.add_dependency "diff-lcs" if windows_build
 end