mruby released in 2012 and 6 years have passed. I have embedded mruby into a lot of middleware like ngx_mruby, and have designed and implemented both extensibility and performance compatibility in middleware. I want to share not only the specifications and background but also design and implementation that only I know for embedding mruby into middleware since I have been sending patches of specifications and features to mruby. In this presentation, I generalize the design and implementation to connect middleware supporting Internet service with mruby and introduce it as a design pattern.