class Jets::Builders::LambdaLayer

def build

Then replace the binary gems.
We consolidate all gems to stage/opt.
At this point gems are in the stage/code and stage/rack folders still. 
def build
  consolidate_gems_to_opt
  replace_compiled_gems
end

def consolidate_gems_to_opt

For Lambda Layer structure

ruby/gems/2.5.0
To:
vendor/gems/ruby/2.5.0
Also restructure the folder from: 
def consolidate_gems_to_opt
  src = "#{stage_area}/code/vendor/gems/ruby/2.5.0"
  dest = "#{stage_area}/opt/ruby/gems/2.5.0"
  rsync_and_link(src, dest)
  return unless Jets.rack?
  src = "#{stage_area}/rack/vendor/gems/ruby/2.5.0"
  rsync_and_link(src, dest)
end

def replace_compiled_gems


stage/code/vendor/gems/ruby/2.5.0 -> /opt/ruby/gems/2.5.0

Then:

to stage/opt/ruby/gems/2.5.0
from stage/code/vendor/gems/ruby/2.5.0

Layers structure and creates a symlinks to it. First:
binary extensions: a good state. This method moves these gems to the Lambda
After this point, gems have been replace in stage/code/vendor/gems with their

move binary gems from opt/ruby/gems/2.5.0 to vendor/gems/ruby/2.5.0
extract binary gems in opt/ruby/gems/2.5.0
remove binary gems in vendor/gems/ruby/2.5.0
replace_compiled_gems: 
def replace_compiled_gems
  project_root = "#{stage_area}/opt"
  headline "Replacing compiled gems with AWS Lambda Linux compiled versions: #{project_root}"
  options = {
    s3: "lambdagems2",
    build_root: cache_area, # used in jets-gems
    project_root: project_root, # used in gem_replacer and jets-gems
  }
  GemReplacer.new(options).run
end

def rsync_and_link(src, dest) 

def rsync_and_link(src, dest)
  FileUtils.mkdir_p(dest)
  # Trailing slashes are required
  sh "rsync -a --links #{src}/ #{dest}/"
  FileUtils.rm_rf(src) # blow away original 2.5.0 folder
  # Create symlink that will point to the gems in the Lambda Layer:
  #   stage/opt/ruby/gems/2.5.0 -> /opt/ruby/gems/2.5.0
  FileUtils.ln_sf("/opt/ruby/gems/#{Jets::Gems.ruby_folder}", src)
end