12.2 Membership and roles

1. A node finds seed nodes and joins the membership (SWIM protocol). An implementation SHOULD detect a suspected node failure within 1–2 s.
2. The coordinator is a Raft group of 3 or 5 nodes of the journal role (the first nodes if there is none). It stores the role assignment, the shard map, the service registry and the dynamic config.
3. The role is determined by assign by: an environment variable, a pod label, auto — the coordinator assigns the role with the greatest deficit up to replicas, taking needs into account.
4. A node brings up only the objects of its roles and publishes to the registry: id, roles, zone, address, load, binary version.
5. Nodes of different versions may run simultaneously (rolling upgrade); compatibility is ensured by §9.2.

Source: docs/spec/oxl-standard.en.md