I think Fly is doing great stuff, and I think they’re a great default for deployment. That said, I think there’s still a LOT of us deploying Phoenix in more traditional cloud environments, or in even more traditional servers. Fly is definitely not the majority of deployments, and I would be surprised if they were a plurality.

I am not a Fly expert, but my sense is that they help in two ways:

1. LiveView in particular adds client → server round trips for rendering that often do not hit the database. These are helped by having the app closer to the client.
2. Fly has global replicas for postgres, which basically let you have read replicas colocated near your apps near your users at the edge. This doesn’t help writes, but it definitely cuts down on latencies for reads.

Look up Mark Ericksen’s talk at last year’s ElixirConf for more details. It’s some clever stuff.

From polls, conversations, and a lot of support I can confidently say elixir apps are deployed all over the place: GCP, AWS, Heroku, Render, Gigalixir, Hetzner, and Fly come up regularly (though Gifalixir and Heroku are declining).