Reshard a Kinesis Data Stream and manage the KCL lease table during the transition

Steps

1. Determine current shard count and target: aws kinesis describe-stream-summary then call UpdateShardCount with TargetShardCount; Kinesis supports doubling or halving shard count in one call
2. Wait for the stream to return to ACTIVE status; parent shards transition to CLOSED while child shards become ACTIVE
3. KCL workers discover new shards via the lease table in DynamoDB; KCL creates new lease entries for child shards automatically and marks parent shard leases as completed once all records are processed
4. Ensure KCL workers checkpoint the parent shard to SHARD_END before processing child shards; KCL enforces this ordering — child shard processing begins only after parent completion
5. Monitor the KCL DynamoDB lease table: confirm child shard lease rows appear and are assigned to workers; stale parent leases with no checkpoint near SHARD_END indicate a processing backlog
6. After resharding stabilize, review provisioned throughput costs: each shard has a base cost; reduce shard count again if utilization is low