add migration

lib/customer_service/release.ex

@@ -0,0 +1,30 @@
+defmodule CustomerService.Release do
+  @moduledoc """
+  Used for executing DB release tasks when run in production without Mix
+  installed.
+  """
+  @app :customer_service
+
+  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 rollback(repo, version) do
+    load_app()
+    {:ok, _, _} = Ecto.Migrator.with_repo(repo, &Ecto.Migrator.run(&1, :down, to: version))
+  end
+
+  defp repos do
+    Application.fetch_env!(@app, :ecto_repos)
+  end
+
+  defp load_app do
+    # Many platforms require SSL when connecting to the database
+    Application.ensure_all_started(:ssl)
+    Application.ensure_loaded(@app)
+  end
+end