Releases should be able to use Mix commands. You might need to adjust your mix deps to include Mix/Ecto-Migrator libraries for your build. Otherwise you can do what people use for sqlite3 migrations in Nerves [1]. Just call it via the library functions instead of via the command line like in `migrate_repo!/1`.

1: https://embedded-elixir.com/post/2017-09-22-using-ecto-and-s...