bitwalker

defmodule Features do
  use GenServer
  
  @features [chat: true]
  
  def enable(feature), do: GenServer.call(__MODULE__, {:toggle, feature, true})
  def disable(feature), do: GenServer.call(__MODULE__, {:toggle, feature, false})
  
  def enabled?(feature) do
    case :ets.lookup(__MODULE__, feature) do

bitwalker

This is not meant to be comprehensive, a guide, or anything quite that sophisticated, just a couple
notes on what I do at work, in production, and how my environment is set up.

Overview:

- Infrastructure runs on AWS
- We run an internal PaaS based on OpenShift Origin/Kubernetes
- We push code to GitHub, which triggers a webhook, which in turn
  triggers OpenShift to start a build, which fetches the source
  code, and runs the build using the Dockerfile contained in the

bitwalker

FROM bitwalker/alpine-erlang:latest
MAINTAINER Paul Schoenfelder <paulschoenfelder@gmail.com>

ENV REFRESHED_AT=2016-06-21 \
    HOME=/opt/app/ \
    MIX_ENV=prod \
    TERM=xterm \
    APP=myapp \
    APPVER=0.1.0

bitwalker

FROM bitwalker/alpine-erlang:latest
MAINTAINER Paul Schoenfelder <paulschoenfelder@gmail.com>

ENV REFRESHED_AT=2016-06-21 \
    HOME=/opt/app/ \
    MIX_ENV=prod \
    TERM=xterm \
    REPLACE_OS_VARS=true

EXPOSE 5000

bitwalker

defmodule Config do
  @moduledoc """
  This module handles fetching values from the config with some additional niceties
  """

  @doc """
  Fetches a value from the config, or from the environment if {:system, "VAR"}
  is provided.

  An optional default value can be provided if desired.

bitwalker

#!/usr/bin/env bash
set -x

term_handler() {
  echo "Stopping the server process with PID $PID"
  erl -noshell -name "term@127.0.0.1" -eval "rpc:call('app@127.0.0.1', init, stop, [])" -s init stop
  echo "Stopped"
}

trap 'term_handler' TERM INT

bitwalker

defmodule Config do
  @moduledoc """
  This module handles fetching values from the config with some additional niceties
  """

  @doc """
  Fetches a value from the config, or from the environment if {:system, "VAR"}
  is provided.

  An optional default value can be provided if desired.

bitwalker

[centos@ip-172-22-245-135 ~]$ sudo iptables -L -n -v
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
 681K  129M ACCEPT     all  --  tun0   *       0.0.0.0/0            0.0.0.0/0            /* traffic from docker for internet */
 743K  517M ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0            multiport dports 4789 /* 001 vxlan incoming */
2825K 2958M ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0            state RELATED,ESTABLISHED
  336 29457 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0
59589 3575K ACCEPT     all  --  lo     *       0.0.0.0/0            0.0.0.0/0
 1786 99404 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            state NEW tcp dpt:22
 6827  429K OS_FIREWALL_ALLOW  all  --  *      *       0.0.0.0/0            0.0.0.0/0

bitwalker

# This is our function definition,
# It is body (not tail) recursive, as it must wait for
# len(tail) to return before the addition can be performed
# on each iteration
def len([]), do: 0
def len([head | tail]), do: 1 + len(tail)

# If we call len([1, 2, 3]), this is what happens
len([1, 2, 3]) == 1 + len([2, 3])
len([2, 3]) == 1 + len([3])

bitwalker

defmodule MyApp do
  use Application
  
  def start(_type, _args) do
    import Supervisor.Spec, warn: false
    
    :ok = handle_args!
    
    children = []
    Supervisor.start_link(children, strategy: :one_for_one, name: MyApp.Supervisor)