Given the highly variable (but, I assume, predictable) load spikes, an elastic service like AWS will probably be your best bet; you can chuck more app servers into the pool during load spikes to keep things going. There’s nothing special about Discourse from a scaling and HA perspective, it’s just a regular ol’ Docker-enabled Rails application with PostgreSQL and Redis; any guide out there dealing with scaling those technologies will give you what you need to know to make Discourse do well. That’s not to say it’s easy; reliably scaling any technology in the face of large load spikes takes a fair chunk of work, but there’s nothing Discourse-specific in there.