[rubyfan]

15 years ago I worked on a couple of really high profile rails sites. We had millions of users with Rails and a single mysql instance (+memcached and nginx). Back then ruby was a bit slower than it is today but I’m certain some of the challenges you face at that scale are things people still do today…

1. try to make most things static-ish reads and cache generic stuff, e.g. most things became non-user specific HTML that got cached as SSI via nginx or memcached

2. move dynamic content to services to load after static-ish main content, e.g. comments, likes, etc. would be loaded via JSON after the page load

3. Move write operations to microservices, i.e. creating new content and changes to DB become mostly deferrable background operations

I guess the strategy was to do as much serving of content without dipping into ruby layer except for write or infrequent reads that would update cache.