can't seed with flyctl ssh console -C '/app/bin/rails db:seed'

It looks like you are using the new Rails Dockerfiles, just released yesterday. These are being developed to match and ideally be included in Rails 7. See Cut over to Rails Dockerfile Generator on Sunday 29 Jan 2023

A few things to be aware of:

  • If your app is Rails 6 or later you don’t need to run db:seed as bin/docker-entrypoint will run db:prepare. See: Rails 6 adds db:prepare rake task | Saeloun Blog
  • Your app is now at /rails instead of /app.
  • If you want to run /rails/bin/rails commands directly from flyctl ssh console, you will need to update your dockerfile. This can be done with one command: Dockerfiles and fly.toml · Fly Docs
  • lib/tasks/fly.rake are no longer used by the build process. Feel free to delete this file.