Understanding WebSocket system messages in elastic channels

The Amazon Chime SDK sends system messages to all connected clients for events that take place in channels. The following list describes the system messages for elastic channels.

Message events

Event payloads for elastic channels contain the subChannelId field. Payloads for non-elastic channels remain the same.

Membership events

The CREATE_CHANNEL_MEMBERSHIP and DELETE_CHANNEL_MEMBERSHIP events now have the subChannelId field in their payloads.

Elastic channels don't support the BATCH_CREATE_CHANNEL_MEMBERHSIP event. When you call the BatchCreateChannelMembership API, the system sends individual CREATE_CHANNEL_MEMBERSHIP events.

You can now use the UPDATE_CHANNEL_MEMBERSHIP event type to signal changes in membership information. For example, during a member transfer from one sub-channel to another, the system sends an UPDATE_CHANNEL_MEMBERSHIP event with the new SubChannelId in the payload to indicate that the member was transferred.

Note

The system only sends the UPDATE_CHANNEL_MEMBERSHIP event to the member that was transferred, and not to other members of the sub-channel. For this reason, we encourage you to use the ListChannelMemberships API instead of WebSockets to populate your channel membership rosters. For more information, refer to Using WebSockets to receive messages.