Scenario

We are using Triplex to manage our multi-schema Postges DB. We deploy using Mix releases, thus Mix is not available and we cannot migrate using the Triplex Mix tasks. We run our public schema migrations via a similar Release module to the one recommended in the Phoenix documentation. To that basic structure, we added an additional migrate_tenants/0 function:

defmodule MyApp.Release do
  @app :my_app

  def migrate do
    load_app()

    for repo <- repos() do
      {:ok, _, _} = Ecto.Migrator.with_repo(repo, &Ecto.Migrator.run(&1, :up, all: true))
    end
  end

  def migrate_tenants do
    load_app()

    for repo <- repos() do
      for tenant <- Triplex.all(repo) do
        Triplex.migrate(tenant, repo)
      end
    end
  end

  defp repos do
    Application.fetch_env!(@app, :ecto_repos)
  end

  defp load_app do
    Application.load(@app)
  end
end

Problem

The migrate_tenants function succeeds when run via a remote IEx session or rpc, but fails when run via eval, ie bin/my_app eval "MyApp.Release.migrate_tenants()". This is in contrast to the migrate function. The error observed is the following:

** (RuntimeError) could not lookup Ecto repo MyApp.Repo because it was not started or it does not exist
    lib/ecto/repo/registry.ex:19: Ecto.Repo.Registry.lookup/1
    lib/ecto/adapter.ex:127: Ecto.Adapter.lookup_meta/1
    lib/ecto/adapters/sql.ex:404: Ecto.Adapters.SQL.query/4
    lib/ecto/adapters/sql.ex:362: Ecto.Adapters.SQL.query!/4
    lib/triplex.ex:289: Triplex.all/1
    (myapp 0.1.0) lib/myapp/release.ex:21: anonymous fn/2 in MyApp.Release.migrate_tenants/0
    (elixir 1.11.4) lib/enum.ex:2193: Enum."-reduce/3-lists^foldl/2-0-"/3
    (myapp 0.1.0) lib/myapp/release.ex:20: MyApp.Release.migrate_tenants/0

Questions

• Is it possible to migrate tenants using Triplex via eval on a release?
• Is there a known root cause for this issue?
• Is there a recommended approach for using Triplex with Mix releases in general?

Note: I posted this as an issue on the Triplex repo several weeks ago, but there have been no responses thus far.