Merge pull request #14 from ktheory/stack-outputs

Support stack outputs as parameters in cfn-flow.yml

Author: ktheory

README.md

@@ -184,6 +184,21 @@ stack:
       # Your parameters, e.g.:
       vpcid: vpc-1234
       ami: ami-abcd
+
+      ##
+      # Use outputs from other stacks
+
+      # This set the `load_balancer` parameter to the value of the
+      # `elbname` output of `my-elb-stack`
+      load_balancer:
+        stack: my-elb-stack
+        output: elbname
+
+      # If you don't specify the output name, it's assumed to be same
+      # as the parameter key:
+      ssh_security_group:
+        stack: my-bastion-stack
+
     disable_rollback: true,
     timeout_in_minutes: 1,
     notification_arns: ["NotificationARN"],
@@ -229,6 +244,23 @@ stack:
     git_sha: <%= `git rev-parse --verify HEAD`.chomp %>
 ```
 
+#### Use stack outputs as parameters
+`cfn-flow` lets you easily reference stack outputs as parameters for new stacks.
+
+```yaml
+# cfn-flow.yml
+stack:
+  parameters:
+    # Set my-param to the `my-param` output of `another-stack`
+    my-param:
+      stack: another-stack
+
+    # Set my-param to the `my-output` output of `another-stack`
+    my-param:
+      stack: another-stack
+      output: my-output
+```
+
 ## Usage
 
 Getting help:

lib/cfn_flow.rb

@@ -39,43 +39,11 @@ def stack_params(environment)
       unless config['stack'].is_a? Hash
         raise Thor::Error.new("No stack defined in #{config_path}. Add 'stack: ...'.")
       end
+      params = StackParams.expanded(config['stack'])
 
-      # Dup & symbolize keys
-      params = config['stack'].map{|k,v| [k.to_sym, v]}.to_h
-
-      # Expand params
-      if params[:parameters].is_a? Hash
-        expanded_params = params[:parameters].map do |key,value|
-          { parameter_key: key, parameter_value: value }
-        end
-        params[:parameters] = expanded_params
-      end
-
-      # Expand tags
-      if params[:tags].is_a? Hash
-        tags = params[:tags].map do |key, value|
-          {key: key, value: value}
-        end
-
-        params[:tags] = tags
-      end
-
-      # Append CfnFlow tags
-      params[:tags] ||= []
-      params[:tags] << { key: 'CfnFlowService', value: service }
-      params[:tags] << { key: 'CfnFlowEnvironment', value: environment }
-
-      # Expand template body
-      if params[:template_body].is_a? String
-        begin
-          body = CfnFlow::Template.new(params[:template_body]).to_json
-          params[:template_body] = body
-        rescue CfnFlow::Template::Error
-          # Do nothing
-        end
-      end
-
-      params
+      params.
+        add_tag('CfnFlowService' => service).
+        add_tag('CfnFlowEnvironment' => environment)
     end
 
     def template_s3_bucket
@@ -113,6 +81,7 @@ def cfn_resource
     # Clear aws sdk clients & config (for tests)
     def clear!
       @config = @cfn_client = @cfn_resource = nil
+      CachedStack.stack_cache.clear
     end
 
     # Exit with status code = 1 when raising a Thor::Error
@@ -131,6 +100,8 @@ def exit_on_failure=(value)
   end
 end
 
+require 'cfn_flow/cached_stack'
+require 'cfn_flow/stack_params'
 require 'cfn_flow/template'
 require 'cfn_flow/git'
 require 'cfn_flow/event_presenter'

lib/cfn_flow/cached_stack.rb

@@ -0,0 +1,32 @@
+module CfnFlow
+  class CachedStack
+
+    class MissingOutput < StandardError; end
+
+    def self.stack_cache
+      @stack_cache ||= {}
+    end
+
+    def self.get_output(stack:, output:)
+      new(stack).output(output)
+    end
+
+    attr_reader :stack_name
+
+    def initialize(stack_name)
+      @stack_name = stack_name
+    end
+
+    def output(name)
+      output = stack_cache.outputs.detect{|out| out.output_key == name }
+      unless output
+        raise MissingOutput.new("Can't find outpout #{name} for stack #{stack_name}")
+      end
+      output.output_value
+    end
+
+    def stack_cache
+      self.class.stack_cache[stack_name] ||= CfnFlow.cfn_resource.stack(stack_name).load
+    end
+  end
+end

lib/cfn_flow/stack_params.rb

@@ -0,0 +1,71 @@
+module CfnFlow
+  # Extend hash with some special behavior to generate the
+  # style of hash aws-sdk expects
+  class StackParams < Hash
+
+    def self.expanded(hash)
+      self[hash].
+        with_symbolized_keys.
+        with_expanded_parameters.
+        with_expanded_tags.
+        with_expanded_template_body
+    end
+
+    def with_symbolized_keys
+      self.inject(StackParams.new) do |accum, pair|
+        key, value = pair
+        accum.merge(key.to_sym => value)
+      end
+    end
+
+    def with_expanded_parameters
+      return self unless self[:parameters].is_a? Hash
+
+      expanded_params = self[:parameters].map do |key,value|
+        { parameter_key: key, parameter_value: fetch_value(key, value) }
+      end
+
+      self.merge(parameters: expanded_params)
+    end
+
+    def with_expanded_tags
+      return self unless self[:tags].is_a? Hash
+
+      tags = self[:tags].map do |key, value|
+        {key: key, value: value}
+      end
+
+      self.merge(tags: tags)
+    end
+
+    def add_tag(hash)
+      new_tags = hash.map do |k,v|
+        {key: k, value: v }
+      end
+      tags = (self[:tags] || []) + new_tags
+      self.merge(tags: tags)
+    end
+
+    def with_expanded_template_body
+      return self unless self[:template_body].is_a? String
+      body = CfnFlow::Template.new(self[:template_body]).to_json
+      self.merge(template_body: body)
+    rescue CfnFlow::Template::Error
+      # Do nothing
+      self
+    end
+
+    def fetch_value(key, value)
+      # Dereference stack output params
+      if value.is_a?(Hash) && value.key?('stack')
+        stack_name = value['stack']
+        stack_output_name = value['output'] || key
+
+        value = CachedStack.get_output(stack: stack_name, output: stack_output_name)
+      else
+        value
+      end
+    end
+    private :fetch_value
+  end
+end

lib/cfn_flow/version.rb

@@ -1,3 +1,3 @@
 module CfnFlow
-  VERSION = '0.8.0'
+  VERSION = '0.9.0'
 end

spec/cfn_flow/cached_stack_spec.rb

@@ -0,0 +1,71 @@
+require_relative '../helper'
+
+describe 'CfnFlow::CachedStack' do
+  subject { CfnFlow::CachedStack }
+
+  describe '.stack_cache' do
+    it 'defaults to a hash' do
+      subject.stack_cache.must_equal({})
+    end
+  end
+
+  describe '.get_output' do
+    let(:output_value) { 'myvalue' }
+
+    before do
+      Aws.config[:cloudformation]= {
+        stub_responses: {
+          describe_stacks: { stacks: [ stub_stack_data.merge(outputs: [{ output_key: "myoutput", output_value: output_value } ]) ] }
+        }
+      }
+    end
+
+    it 'returns the output' do
+      subject.get_output(stack: 'mystack', output: 'myoutput').must_equal output_value
+    end
+
+    it 'has required kwargs' do
+      -> { subject.get_output }.must_raise(ArgumentError)
+    end
+  end
+
+  describe 'an instance' do
+    subject { CfnFlow::CachedStack.new('mystack') }
+    let(:output_value) { 'myvalue' }
+
+    before do
+      Aws.config[:cloudformation]= {
+        stub_responses: {
+          describe_stacks: { stacks: [ stub_stack_data.merge(outputs: [{ output_key: "myoutput", output_value: output_value } ]) ] }
+        }
+      }
+    end
+
+    it "should return the output value" do
+      subject.output('myoutput').must_equal output_value
+    end
+
+    describe "with a missing output" do
+      it "should raise an error" do
+        -> { subject.output("no-such-output") }.must_raise(CfnFlow::CachedStack::MissingOutput)
+      end
+    end
+
+    describe "with a missing stack" do
+
+      subject { CfnFlow::CachedStack.new('no-such-stack') }
+      before do
+        Aws.config[:cloudformation]= {
+          stub_responses: {
+            describe_stacks: 'ValidationError'
+          }
+        }
+      end
+
+      it "should raise an error" do
+        -> { subject.output('blah') }.must_raise(Aws::CloudFormation::Errors::ValidationError)
+      end
+    end
+  end
+
+end