clustering

Clustering class implements simple clustering logic through etcd as a distributed consistent key-value store. A on_stable callback is fired for the leader once the cluster has stabilized.

Running $ shards build will create a simple proof of concept app, run it with ./bin/poc

Usage

The stabilize : Array(NamedTuple(ip: String, port: Int32)) -> Void arg of Clustering defines the class's stabilization logic that is fired upon cluster join, leave, and election events. The array of node data is all of the nodes in the cluster.

Implementation

A single etcd lease is granted per node so if a node drops out of the cluster, all associated key/values will expire from the cluster.

Watchfeeds

There are 4 etcd watchfeeds

• election: notify nodes still in cluster that there is no longer a leader
• readiness: propagate readiness against a cluster version
• version: set by leader when there's a change in cluster state, nodes must 'ready' themselves to this signal
• discovery: keeps track of nodes in etcd under a service namespace

Dependencies

• etcd ~> v3.3