My naive attempt to implement distributed CRDT PN-Counter

git clone https://github.com/svenyurgensson/pn_counter_elixir.git pn_counter

cd pn_counter/
mix deps.get

Master node should be started as:

elixir --name counter --cookie sound -S mix run --no-halt

Server has predefined master node [email protected] It should be changed to something more acceptable in lib/pn_counter/counter.ex

Worker node should be started as:

elixir --name %NAME% --cookie sound -S mix run --no-halt

Where %NAME% represents name of given node

Get current counter value:

>curl -i -X GET http://localhost:8000/counter
HTTP/1.1 200 OK
connection: keep-alive
server: Cowboy
date: Tue, 15 Oct 2013 04:32:47 GMT
content-length: 1
0

Increment value:

>curl -i -X POST http://localhost:8000/counter/increment
HTTP/1.1 201 Created
connection: keep-alive
server: Cowboy
date: Tue, 15 Oct 2013 04:34:37 GMT
content-length: 0

>curl -i -X GET http://localhost:8000/counter
HTTP/1.1 200 OK
connection: keep-alive
server: Cowboy
date: Tue, 15 Oct 2013 04:35:12 GMT
content-length: 1
1

Decrement value:

>curl -i -X POST http://localhost:8000/counter/decrement
HTTP/1.1 201 Created
connection: keep-alive
server: Cowboy
date: Tue, 15 Oct 2013 04:51:18 GMT
content-length: 0

Here are links to more info about Convergent Replicated Data Types (the state-based variant):

• A comprehensive study of Convergent and Commutative Replicated Data Types [PDF] - This describes the concepts behind CRDTs, both state-based (convergent, aka CvRDTs) and operation-based (commutative, aka CmRDTs).
• basho/riak_kv riak_kv_counter.erl - The source code of the counter implementation, with notes about which CRDT is actually used (PN-Counters, if you're wondering).
• Data Structures in Riak - RICON 2012 - A talk by Sean Cribbs and Russell Brown at RICON 2012, including a proof-of-concept implementation of CRDTs in Riak. There's a demo at about 28:30 that shows what happens during and after a network partition.
• A Cookbook full of Tutorials to get Developers started with Riak's CRDTs