How to run Triplex tenant migrations when deploying via mix release?

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.

This is what we’re doing for our release module:

def migrate do
  {:ok, _} = Application.ensure_all_started(:my_app)

  migrate_public_schema()
  migrate_tenant_schemas()
end

defp migrate_public_schema do
  path = Application.app_dir(:my_app, "priv/repo/migrations")
  Migrator.run(MyApp.Repo, path, :up, all: true)
end

defp migrate_tenant_schemas do
  path = Application.app_dir(:my_app, "priv/repo/tenant_migrations")

  Accounts.list_tenants()
  |> Enum.each(&Migrator.run(MyApp.Repo, path, :up, all: true, prefix: &1.prefix))
end

Wasn’t aware of the Triplex.all function, I could probably replace the call to our Accounts module with that, but anyway using the Migrator.run function instead of Triplex.migrate has worked for us.

3 Likes

Thanks for the suggestion @riebeekn . It seems that you just work around Triplex entirely. I’ll give that a shot.
If you try switching to Triplex.all - I would be very curious to hear if you run into the same issue we have.

Looks like Triplex.all just returns the schema prefixes so that should be fine, i.e.

Triplex.all()
|> Enum.each(&Migrator.run(MyApp.Repo, path, :up, all: true, prefix: &1))

@riebeekn - This is what I have working now. Thanks again for steering me in the right direction.

defmodule MyApp.Release do
  @moduledoc """
  Used for executing DB release tasks when run in production without Mix
  installed.
  """

  alias Ecto.Migrator
  alias MyApp.Repo
  alias MyApp.Tenants

  @app :my_app

  def migrate_public_schema do
    load_app()

    {:ok, _, _} = Migrator.with_repo(Repo, &Migrator.run(&1, :up, all: true))
  end

  def migrate_tenant_schemas do
    load_app()

    Migrator.with_repo(Repo, fn repo ->
      Tenants.list_tenants()
      |> Enum.each(
        &Migrator.run(repo, tenant_migrations_path(), :up, all: true, prefix: &1.schema_name)
      )
    end)
  end

  def rollback_public_schema(version) do
    load_app()

    {:ok, _, _} = Migrator.with_repo(Repo, &Migrator.run(&1, :down, to: version))
  end

  def rollback_tenant_schemas(version) do
    load_app()

    Migrator.with_repo(Repo, fn repo ->
      Tenants.list_tenants()
      |> Enum.each(
        &Migrator.run(repo, tenant_migrations_path(), :down, to: version, prefix: &1.schema_name)
      )
    end)
  end

  defp tenant_migrations_path() do
    Triplex.migrations_path(Repo)
  end

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