Kafka LeaveGroup Request Wire Format v3 — Binary Protocol Layout

What is LeaveGroup?

Sent on clean consumer shutdown to trigger an immediate rebalance rather than waiting for the session timeout. Without it, a departed consumer's partitions stay unassigned for up to session.timeout.ms. Static membership (group.instance.id) avoids rebalances on short restarts by skipping LeaveGroup semantics.

Schema
{
  "GroupId": string,
  "Members": [{
      "MemberId": string,
      "GroupInstanceId": string?
  }]
}

Example
{
  "GroupId": "order-processors",
  "Members": [{
      "MemberId": "consumer-1-abc123",
      "GroupInstanceId": "instance-0"
  }]
}