[Spivak]

Discord and Slack do the article's suggestion of using web sockets for the receiving side only (mostly) and having you switch to http on the calling side. It works pretty well, you have to keep two sets of books but the web socket side is almost always for events that you, the client, should be responding to so it works somewhat like a reverse http but that works with your firewall. It also allows Discord to implement trivial, from the client's perspective, sharding. It really is clever as hell, scaling up a bot/integration is as easy as just turning on sharding and launching multiple instances of your bot. It handles spreading events across them.

The author throws away their own suggestion but it clearly works, works well, and scales well into "supermassive" size. They don't even mention the real downside to web sockets which is that they're stateful and necessarily tied to a particular server which makes them not mesh at all with your stateless share-nothing http servers.