Kinesis partition skew from unbalanced keys
An IoT ingestion pipeline writes device telemetry to a Kinesis stream (8 shards), using `region_code` as the partition key. At 12:00 producers start getting `ProvisionedThroughputExceededException` (write throttling) on *some* records, but aggregate stream `IncomingBytes` is well under the 8-shard write budget (16 MB/s). The CloudWatch shard-level `WriteProvisionedThroughputExceeded` metric is high on exactly 2 of the 8 shards; the other 6 are nearly idle. Recent context: most traffic comes from two `region_code` values (`us-east`, `eu-west`) covering ~80% of devices. Triage and mitigate the write throttling despite spare aggregate capacity.
Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.