Custom mix task for development environments to start/stop a Postgres database in a Docker container

docker.db.exs

defmodule Mix.Tasks.Docker.Db do
  use Mix.Task

  @project_name "Program Builder"
  @project_sname "program_builder"

  @shortdoc "Start/stop the docker Postgres container for development"

  @moduledoc """
  Fire up a postgres database for #{@project_name}, named #{@project_sname} in Docker.

  ## Usage:

      $ mix docker.db start
      $ mix docker.db stop
  """

  @impl Mix.Task
  def run(["start"]) do
    Mix.shell().info("Starting container named #{@project_sname}...")
    volume = "#{@project_sname}_volume"

    System.cmd("docker", [
      "run",
      "--rm",
      "-d",
      "-e",
      "POSTGRES_PASSWORD=postgres",
      "-p",
      "5432:5432",
      "--mount",
      "type=volume,src=#{volume},dst=/var/lib/postgresql",
      "--name",
      @project_sname,
      "postgres"
    ])

    Mix.shell().info("done.")
  end

  @impl Mix.Task
  def run(["stop"]) do
    System.cmd("docker", ["stop", @project_sname])
    Mix.shell().info("Container #{@project_sname} stopped")
  end
end

Stuff this in a file at lib/mix/tasks/docker.db.exs, recompile with mix compile and you should be good to go!