Improve multi node support and control

[jbernardo95]

Currently if cronex is started in multiple nodes, cron jobs will run several times in different nodes.

The desired behaviour is to have multiple cronex instances that coordinate between them which one should run the cron jobs.

[manuel-rubio]

@jbernardo95 in Erlang you can fix this using the distribution configuration for the kernel application. Actually you can use it in Elixir as well:

https://dockyard.com/blog/2016/01/28/running-elixir-and-phoenix-projects-on-a-cluster-of-nodes

And the configuration could be:

config :kernel,
  sync_nodes_mandatory: [:"node1@host", :"node2@host"],
  distributed: [{:cronex, [:"node1@host", :"node2@host"]}]

This way cronex will run only in one of the nodes. If the node where is running is turned off then the application is started in the other one.

[jbernardo95]

@manuel-rubio I didn't know about this.

Seems to be very nice way to handle this problem. I will definitely look into this.

Thank you !

[pggalaviz]

Maybe multi node functionality can be improved with something like a CRDT?
This project looks really promising: https://github.com/derekkraan/delta_crdt_ex
Great explanation about it here.

[jbernardo95]

Thank you for the insight @pggalaviz ! Definitely something to look into.