# `Nebulex.Distributed.RingMonitor`
[🔗](https://github.com/elixir-nebulex/nebulex_distributed/blob/v3.2.3/lib/nebulex/distributed/ring_monitor.ex#L1)

A `GenServer` that keeps the consistent hash ring in sync with the
current cluster topology for distributed Nebulex adapters.

The RingMonitor is started automatically as part of the partitioned
cache supervision tree. It performs the following duties:

  * **Cluster subscription** - Subscribes to Erlang's `:pg` (process
    groups) via `Nebulex.Distributed.Cluster.monitor_scope/0` to
    receive join and leave notifications for the cache's group.

  * **Ring synchronisation** - When nodes join or leave the cluster,
    the RingMonitor adds or removes them from the `ExHashRing.Ring`,
    ensuring key-to-node mappings stay up to date.

  * **Periodic rejoin** - To handle race conditions during concurrent
    cluster startup (where some nodes may miss initial join events),
    the RingMonitor periodically rejoins the `:pg` group at the
    interval configured by `:rejoin_interval` (default: 30 seconds).
    Because `:pg` joins are idempotent, this forces all nodes to
    refresh their ring view and guarantees eventual consistency.

## Telemetry events

The RingMonitor emits Telemetry events under
`telemetry_prefix ++ [:ring_monitor, event]`. See the
"Adapter-specific telemetry events" section in
`Nebulex.Adapters.Partitioned` for the full list of events,
measurements, and metadata.

# `child_spec`

Returns a specification to start this module under a supervisor.

See `Supervisor`.

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*Consult [api-reference.md](api-reference.md) for complete listing*