Broker deep dive

Broker is a component of AnyCable-Go responsible for keeping streams, sessions and presence information in a cache-like storage. It drives the Reliable Streams and Presence features.

Broker implements features that can be characterized as hot cache utilities:

• Handling incoming broadcast messages and storing them in a cache—that could help clients to receive missing broadcasts (triggered while the client was offline, for example).
• Persisting client states—to make it possible to restore on re-connection (by providing a session id of the previous connection).
• Keeping per-channel presence information.

Client-server communication

Below you can see the diagram demonstrating how clients can use the broker-backed features to keep up with the stream messages and restore their state:

To support these features, an extended Action Cable protocol is used for communication.

You can use AnyCable JS client library at the client-side to use the extended protocol.

Broadcasting messages

Broker is responsible for registering broadcast messages. Each message MUST be registered once; thus, we MUST use a broadcasting method which publishes messages to a single node in a cluster (see broadcasting). Currently, http and redisx adapters are supported.

NOTE: When legacy adapters are used, enabling a broker has no effect.

To re-transmit registered messages within a cluster, we need a pub/sub component. See Pub/Sub for more information.

The overall broadcasting message flow looks as follows: