Cluster discovery

Cluster discovery will soon be deprecated and will be replaced by Platforms and platforms discovery.

The cluster discovery process aims to keep administration and management overheads at a minimum and take advantage of the highly dynamic platforms and tools available today (“The Cloud”).

So how does cluster discovery work?

Users apply one or more DiscoverySetting objects though the API.
The cluster discovery component periodically runs at fixed intervals. The interval should be short as it determines the delay between discoveries needing to run and them being scheduled.
The discovery run looks for any discoveries with an expected next schedule time in the past. If no cluster discovery needs to run the discovery run does nothing.
The discovery run schedules a discovery task for each discovery that needs to be performed.
The expected next schedule time is updated to now() + discovery interval.
A task worker picks up the discovery task.
The discovery task fetches discovery records from the given discovery.
Discovery records are updated in the primary store.

Deleting clusters and nodes

When clusters and nodes are automatically discovered they can also automatically go away.

This feature is not currently available and is yet to be designed in full.

Why discover clusters?

The primary use case for Replicante is part of an automated, distributed, dynamic infrastructure that scales from a small number of small clusters to a large number of large clusters.

It is assumed that managing a list of nodes is at best impractical, but may even be impossible in combination with tools such as auto scaling groups and automated instance provisioners.

The idea of cluster discovery was inspired by Prometheus. Cluster discovery has several advantages:

A single source of truth as to which instances should exist in which clusters.
Automatic detection of node creation and retirement.
Nodes are “checked” against some form of trusted server inventory (nodes can’t just add themselves to a cluster).