Rails 5 and Chrome Developer Tools Performance Audit (Lighthouse)

I just inherited large legacy app (600k loc) updated to Rails 5.1 and was asked to look into Chrome Developer Performance Audit (Lighthouse) as currently on most pages it gets 7-9 points out of 100 (dev mode, caching on).

I’d like to make it faster and more mobile friendly (it is pretty fast in dev and production on desktop client) and make better score. Any ideas, what else could be done? I did not find anything related to Rails and this performance audit.

Things I tried already:

  • added q_auto:low to images on landing page (sets quality low on images from cloudinary cdn)
  • moved some external js/css to asset pipeline
  • tried loading external js asynchronously
  • optimized most images with image_optim
  • tried image lazy loading
  • tried page caching and partial caching