A simple plug for setting cache-control header with example of defining a pipeline

cache_control.ex

# lib/app/plugs/cache_control.ex
defmodule App.Plugs.CacheControll do
  import Plug.Conn

  def init({val, :seconds}), do: val
  def init({val, :minutes}), do: 60*val
  def init({val, :hours  }), do: 60*60*val
  def init({val, :days   }), do: 24*60*60*val
  def init({val, :weeks  }), do: 7*24*60*60*val
  def init({val, :months }), do: 30*7*24*60*60*val

  def call(conn, seconds) do
    Plug.Conn.put_resp_header(conn, "cache-control", "private, max-age=#{seconds}")
  end
end

router.ex

# web/router.ex
defmodule App.Router do
  import App.Plugs.Cache

  use App.Web, :router

  # <snip>

  pipeline :cache do
    plug App.Plugs.Cache, {12, :months}
  end

  # <snip>
end