Erlang in docker cloud sandbox

This application demostrates how to setup a connection between erlang nodes that are running inside containers which are destributed over the internet.

The application uses:

1. epmdless - a distribution protocol implementation which allows to run erlang nodes without epmd (https://github.com/oltarasenko/epmdless)
2. erlang-node-discovery - service which allows to setup dynamic node discovery accross different hosts (for the case when your application is scheduled on different physical hosts, e.g: Mesos) (https://github.com/oltarasenko/erlang-node-discovery)

EPMDLess example

This short example shows how to use epmdless to connect nodes without epmd

0. Checkout to the epmdless_example branch git checkout epmdless_example
1. Build the docker image with the app inside docker-compose build
2. Run docker-compose up
3. Connect to app3 machine and start sample app in the console mode:

    $ docker-compose exec app3 bash
    $ _build/default/rel/sample_app/bin/sample_app console
    (app3@host1.com)1> epmdless_dist:add_node('app1@host1.com', 17012).
    =ERROR REPORT==== 28-Feb-2018::11:25:48 ===
    Adding a node: 'app1@host1.com'
    ok
    (app3@host1.com)2> epmdless_dist:list_nodes().
    [{'app1@host1.com',{"host1.com",17012}}]
    (app3@host1.com)3> net_adm:ping('app1@host1.com').
    (app3@host1.com)5> nodes().
    ['app1@host1.com']

Which means that you've successfully connected nodes without epmd

Epmdless with node discovery

The only thing you need to organize node discovery is the following config section:

    % epmdless_dist as our database
    {db_callback, epmdless_dist},
    % discovery will happen on one machine only
    {hosts, ["host1.com", "host2.com", "host3.com"]},
    % query following appnames/ports
    {node_ports, [
      {'app1', 17012},
      {'app2', 17013},
      {'app3', 17014}
    ]}
  ]}

Which means that app1,app2 and app3 could be randomly started on host1.com, host2.com or host3.com

Lets try it out:

0. Checkout to the master branch git checkout master
1. Build the docker image with the app inside docker-compose build
2. Run docker-compose up to bring everything up

You will start getting:

2_1  | =INFO REPORT==== 14-Feb-2018::13:09:34 ===
app2_1  | Currently I know ['app1@host1.com','app3@host2.com'] nodes

which means that the nodes were able to discover each other.