Useful for Ruby/Docker SAM Projects

layer_downloader.rb

require 'yaml'
require 'open-uri'
require 'aws-sdk-lambda'

class LayerDownloader

  def download
    File.open(zip_file, 'wb') do |f|
      URI.open(location) { |zip| f.write(zip.read) }
    end
  end

  def location
    layer_info.content.location
  end

  def client
    @client ||= Aws::Lambda::Client.new
  end

  def arn
    @arn ||= cf_data['Mappings']['LayerArn'][region]['development']
  end

  def layer_name
    arn.split(':')[-2]
  end

  def version_number
    arn.split(':')[-1]
  end

  def layer_info
    @layer_info ||= client.get_layer_version(
      layer_name: layer_name,
      version_number: version_number
    )
  end

  def region
    ENV['AWS_REGION'] || 'us-east-1'
  end

  private

  def cf_data
    @cf_data ||= YAML.load(cf_yaml)
  end

  def cf_yaml
    File.read "#{Dir.pwd}/template.yaml"
  end

  def zip_file
    "#{Dir.pwd}/tmp/layer.zip"
  end

end

LayerDownloader.new.download