akkoma/priv/repo/migrations/20190123125546_create_instances.exs

defmodule Pleroma.Repo.Migrations.CreateInstances do
  use Ecto.Migration

  def change do
    create_if_not_exists table(:instances) do
      add :host, :string
      add :unreachable_since, :naive_datetime_usec

      timestamps()
    end

    create_if_not_exists unique_index(:instances, [:host])
    create_if_not_exists index(:instances, [:unreachable_since])
  end
end