Migrations Are Silently Skipped if They Do Not Have an Exs Extension

tl;dr

If you’ve got a migration that has ex as its extension instead of exs its silently skipped.

I’ve recently rerun a complete db migration, but for some reason a table was missing. A closer investigation showed that the migration file wasn’t included in the schema_migrations table, and that the file for some reason had the extension .ex instead of .exs.

The migrations where run after a fresh install of the application, with the Ecto.Migrator.run/4 function like this:

defmodule Migration do
  def migrate do
    {:ok, _} = Application.ensure_all_started(:otp_app)

    path = Application.app_dir(:otp_app, "priv/repo/migrations")
    Ecto.Migrator.run(Repo, path, :up, all: true)
  end
end

Lesson learned: Make sure that your migration files always end with .exs!