Is DB pool returned when migration finished while Releasing via Distillery?

I recently upgraded Phoenix v1.4 from v1.3 as well as Ecto v3.0 from v2.2.

And I found that the requires at least 2 DB pools, so I increased the pool size in the Distillery release tasks like this:

defmodule Nohogu.Tasks.ReleaseTasks do
  @start_apps [:crypto, :ssl, :postgrex, :ecto]
  @repo Nohogu.Repo
  @otp_app :nohogu

  def setup() do
    IO.puts "Loading #{@otp_app}..."
    IO.puts "Starting dependencies.."
    Enum.each(@start_apps, &Application.ensure_all_started/1)

    IO.puts "Creating database if not exists..."

    {:ok, _} = @repo.start_link(pool_size: 2)

    IO.puts "Running migrations...", migrations_path(), :up, all: true)

    # Signal shutdown
    IO.puts "Success!"

  defp migrations_path(), do: Path.join([priv_dir(), "repo", "migrations"])
  defp priv_dir(), do: "#{:code.priv_dir(@otp_app)}"

The two DB pools are used only to check and migrate if there’s a new migrations.

Though there’s no problem occurred yet, I wanted to know whether the pools are returned or occupied. If it’s not returned then please help me making them returned back.