NanoRing is a very very small Cluster management System in Elixir.

NanoRing needs only Elixir 0.11. It uses a simple gossip protocol to share the ring state without a master node. The 2 sets containing the ring state (all nodes and up nodes) are made convergent with a LWW-element-set state-based CRDT (http://hal.upmc.fr/docs/00/55/55/88/PDF/techreport.pdf ). The LWW-element-set containing all nodes is persistent and written on disk.

The state communication works using a gossip style protocol :

• each node has two sets : one containing all cluster nodes, and the other containing only up node.
• every second, a node choose a random node among up-nodes, send it its 2 sets.
• the chosen node updates its own ring merging the received ring.
• the chosen node look if the sending node is in its up-node set, if not add it (because it knows that it has juste received a message from it, so it is not down)
• the chosen node send an "ack" message to the sending node, so that if this node did not receive the ack after a timeout, it can remove the chosen node from its "up-set".

The whole cluster node set is persisted on-disk on each node, saved on cluster change. The up node set is initialized with all nodes.

When a node is removed (cast:del_node), remove it from the node_set but not from the up_set to allow the gossip propagates the ring. When a node see that it is not in its current cluster, delete its ring file and exit the node after 10 seconds, so that all node will remove it from their up_set.

First you can create 4 node launching either make multi_start if you use xterm, it will launch 4 terms with erlang nodes named dev[1,2,3,4]@127.0.0.1 running NanoRing.App.

If you cannot use xterm, you can create your own 4 terminal and launch make start_dev[1-4] on each one.

By default, each node is in a ring containing only itself. To join another node, use for instance on nano_ring_dev1:

:gen_server.cast(NanoRing,{:add_node,:"[email protected]"})

If you want to remove a node, use :

:gen_server.cast(NanoRing,{:del_node,:"[email protected]"})

and wait 10 seconds.

In order to see the evolution of the cluster, you can see the whole cluster with :

:gen_server.call(NanoRing,:get_all)

To observe the available nodes of the cluster, you can use :

:gen_server.call(NanoRing,:get_up)