Kafka SyncGroup Response Wire Format v4 — Binary Protocol Layout

What is SyncGroup?

After JoinGroup, the elected leader pushes computed assignments via SyncGroup, and every member waits for the response to learn its own assignment. A rebalance that completes JoinGroup but hangs here usually means the leader is taking too long to compute assignments (large groups, slow custom assignors).

Schema
{
  "ThrottleTimeMs": int32,
  "ErrorCode": int16,
  "Assignment": bytes
}

Example
{
  "ThrottleTimeMs": 0,
  "ErrorCode": 0,
  "Assignment": "<assignment>"
}