Serverless で layers に gems を配置する

serverless.yml

service: emattsan

provider:
  name: aws
  runtime: ruby2.5
  stage: ${opt:stage, 'development'}
  region: ap-northeast-1

package:
  exclude:
    - package.json
    - yarn.lock
    - node_modules/**
    - Gemfile*
    - vendor/**

# add symbolic link
#     $ (mkdir -p layers/ruby/gems && cd layers/ruby/gems && ln -s ../../../vendor/bundle/ruby/2.5.0 2.5.0)
layers:
  gems:
    path: layers
    name: ${self:service}-${self:provider.stage}-gems
    compatibleRuntimes:
      - ruby2.5
    allowedAccounts:
      - '*'

functions:
  fake:
    handler: handler.fake
    layers:
      - {Ref: GemsLambdaLayer}
  hello:
    handler: handler.hello
    layers:
      - {Ref: GemsLambdaLayer}