VerneMQ 2.2.0

VerneMQ 2.2.0 adds runtime compatibility updates, listener-level configuration improvements, performance options, and operational examples. This page summarizes the most relevant user-facing changes and links to the detailed documentation.

Runtime Support

VerneMQ 2.2.0 supports running on Erlang/OTP 28 and Erlang/OTP 29.

Fanout Sharding

Fanout sharding can increase throughput and lower backpressure for high-frequency publishers where local topic fanout has to deliver to many subscribers. The related advanced settings are fanout.shard_count and fanout.async_handoff.

See Advanced Options.

Subscription Limit Guardrail

The new max_subscriptions_per_client setting limits how many subscriptions a client can have. A value of 0 keeps the default unlimited behavior.

See MQTT Options.

Per-Listener Auth Chains

MQTT listeners can define their own authentication and authorization plugin chains with auth_plugins and authz_plugins. This allows different listeners to use different authentication and authorization behavior without changing the global plugin chain.

See MQTT Listeners and Managing Listeners.

Forward Connection Options

forward_connection_opts can pass listener metadata to auth_on_register and auth_on_register_m5 hooks. Plugins can use that metadata to implement different behavior based on the listener that accepted the client connection.

See MQTT Listeners and Session lifecycle.

Listener active_n

TCP and SSL listeners support active_n, which controls how many incoming TCP packets may be delivered before the socket switches back to passive mode. The default is 1, preserving the previous behavior.

See MQTT Listeners.

WebSocket Anonymous Override

allow_anonymous_override is now available for WebSocket and secure WebSocket listeners as well as TCP and SSL listeners. This allows a named listener to override a global allow_anonymous = off setting.

See MQTT Listeners.

Cluster and Internode Robustness

VerneMQ 2.2.0 improves internode MQTT delivery with a connect-ack handshake, bounded inbound buffering, outgoing batching, and larger default outgoing clustering buffers. These settings are advanced and should usually be left at their defaults.

See Inter-node Communication.

Prometheus Alert Rules Template

VerneMQ ships with a minimal Prometheus alert rules template in metrics_scripts/prometheus/vernemq-alert-rules.yml. The template is intended as a starting point and should be extended or adapted to the thresholds, labels, severities, and runbooks of each deployment.

See Prometheus.