How can I set the connection retry timer in the Ecto Postgrex driver - phoenix-framework

Question

When my application starts, and the database hostname cannot be resolved, the Ecto/Postgrex driver now retries 20 times within the same second, and then Phoenix exits. Here's the error:
failed to connect: ** (DBConnection.ConnectionError) tcp connect (odoodb:5432): non-existing domain - :nxdomain
I want to control the time between retries, and the amount of retries as well. How do I do that? Couldn't find anything in the docs.
BTW: running in docker, so DNS can suddenly start working.
Here are the software versions I use:
{:phoenix, "~> 1.3.0-rc"},
{:phoenix_pubsub, "~> 1.0"},
{:phoenix_ecto, "~> 3.0"},
{:postgrex, ">= 0.0.0"},
{:phoenix_html, "~> 2.6"},
{:phoenix_live_reload, "~> 1.0", only: :dev},
{:gettext, "~> 0.11"},
{:cowboy, "~> 1.0"},
{:distillery, "~> 1.0"},
{:xain, "~> 0.6"},
{:comeonin, "~> 3.0"},
{:ueberauth_identity, "~> 0.2"},
{:ueberauth_github, "~> 0.4"},
{:ueberauth_google, "~> 0.5"},
{:ueberauth_facebook, "~> 0.6"},
{:bamboo, "~> 0.8"},
{:timex, "~> 3.0"},
{:scrivener_ecto, "~> 1.0"},
Here is the code that exits:
defmodule Backend.Application do
use Application
# See http://elixir-lang.org/docs/stable/elixir/Application.html
# for more information on OTP Applications
def start(_type, _args) do
import Supervisor.Spec
# Define workers and child supervisors to be supervised
children = [
# Start the Ecto repository
supervisor(Backend.Web.Repo, []),
# Start the endpoint when the application starts
supervisor(Backend.Web.Endpoint, []),
# Start your own worker by calling: Backend.Worker.start_link(arg1, arg2, arg3)
# worker(Backend.Worker, [arg1, arg2, arg3]),
]
# See http://elixir-lang.org/docs/stable/elixir/Supervisor.html
# for other strategies and supported options
opts = [strategy: :one_for_one, name: Backend.Supervisor]
res = Supervisor.start_link(children, opts)
IO.puts "######### run migrations..."
Ecto.Migrator.run(Backend.Web.Repo, Path.join(["#{:code.priv_dir(:backend)}", "repo", "migrations"]), :up, all: true)
IO.puts "######### migrations done..."
res
end
end
I think it's actually exiting in Migrator.run. Here's the error:
######### run migrations...
08:31:22.774 [info] Application backend exited: exited in: Backend.Application.start(:normal, [])
** (EXIT) an exception was raised:
** (DBConnection.ConnectionError) connection not available because of disconnection
(db_connection) lib/db_connection.ex:925: DBConnection.checkout/2
(db_connection) lib/db_connection.ex:741: DBConnection.run/3
(db_connection) lib/db_connection.ex:1132: DBConnection.run_meter/3
(db_connection) lib/db_connection.ex:584: DBConnection.prepare_execute/4
(ecto) lib/ecto/adapters/postgres/connection.ex:93: Ecto.Adapters.Postgres.Connection.execute/4
(ecto) lib/ecto/adapters/sql.ex:243: Ecto.Adapters.SQL.sql_call/6
(ecto) lib/ecto/adapters/sql.ex:193: Ecto.Adapters.SQL.query!/5
(ecto) lib/ecto/adapters/postgres.ex:86: anonymous fn/4 in Ecto.Adapters.Postgres.execute_ddl/3
(elixir) lib/enum.ex:1755: Enum."-reduce/3-lists^foldl/2-0-"/3
(ecto) lib/ecto/adapters/postgres.ex:86: Ecto.Adapters.Postgres.execute_ddl/3
(ecto) lib/ecto/migrator.ex:43: Ecto.Migrator.migrated_versions/2
(ecto) lib/ecto/migrator.ex:142: Ecto.Migrator.run/4
(backend) lib/backend/application.ex:24: Backend.Application.start/2
(kernel) application_master.erl:273: :application_master.start_it_old/4
So I think my question now becomes: how do I wait for a working connection, or how do I make migrator wait for it?
Also I'd still like to be able to make the driver wait longer between retries.