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.
How does it work ?
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
How to test Nano Ring
First you can create 4 node launching either
make multi_start if you use
xterm, it will launch 4 terms with erlang nodes named
If you cannot use xterm, you can create your own 4 terminal and
make start_dev[1-4] on each one.
Create a cluster
By default, each node is in a ring containing only itself. To join
another node, use for instance on
If you want to remove a node, use :
and wait 10 seconds.
In order to see the evolution of the cluster, you can see the whole cluster with :
To observe the available nodes of the cluster, you can use :