Things to note:

• The hexdocs page on deploying to fly.io is pretty up-to-date, and in general I followed that (starting with the mix phx.new --live part).

• The fly.io walkthrough guide is currently (as of writing) out-of-date—it suggests and old version of Phoenix (v1.5, whereas the latest is v1.6). The main benefit of v1.6 is the move to esbuild (and removal of webpack/npm), which is quite nice from a developer ergonomics perspective. In addition, some of the “you need to change your elixir config” stuff around IPv6 is now no longer needed.

• The default fly.toml file which got created for included config for tcp health checks—which are obviously a good idea, but the default phoenix app created above (by mix phx.new --live ) doesn’t have an endpoint to respond to them afaict (I may be wrong—I don’t know enough about how the framework works yet). There’s some potentially helpful stuff about enabling them in a forum post that I found, but as yet I haven’t set it up—will update this post asap with more info.