CloudFormationのtemplateからRefの依存関係を図示するやつ (要ruby, graphviz)

generate_dependencies_graph.rb

#!/usr/bin/env ruby

require 'json'

template_name = ARGV[0]
contents = File.read(template_name)
json = JSON.parse(contents, symbolize_names: true)

def traverse(hash, &block)
  hash.each {|key, value|
    if value.class == Hash
      traverse value, &block
    elsif value.class == Array
      value.map {|e|
        traverse e, &block if e.class == Hash
      }
    else
      block.call(key, value)
    end
  }
end

def select_refs(resource)
  ret = []
  traverse(resource) {|key,value|
    if key == :Ref
      ret << value.to_sym
    end
  }
  ret
end

def dependencies(resources)
  ret = []
  resources.each {|resource_name, resource_value|
    refs = select_refs(resource_value)
    ret << refs.map {|ref| [resource_name, ref]}
  }
  ret.flatten(1)
end

def output_dots(dependencies)
  ret = 'digraph G {'

  ret += dependencies.map {|child, parent|
    %("#{child}" -> "#{parent}")
  }.join("\n")

  ret += '}'
  ret
end

def reject_params(dependencies, resources)
  resource_names = resources.keys
  dependencies.select {|_child,parent|
    resource_names.include?(parent)
  }
end

resources = json[:Resources]

ret = output_dots(reject_params(dependencies(resources), resources))
File.write('deps.dot', ret)
system('dot -Tpng -o deps.png deps.dot')