With Amazon Data Firehose the only controllable contributor to end-to-end latency is the delivery stream’s buffering hint. Setting the buffer interval to 0 seconds (and using the smallest practical PutRecordBatch size) causes each record to be forwarded to Amazon OpenSearch Service as soon as it is received, eliminating the 60-second wait and allowing sub-second propagation to the dashboard.

B. AWS DataSync is a scheduled bulk-transfer service; it has no concept of streaming or enhanced fan-out consumers, so cannot achieve sub-second latency.

C. Doubling the buffer interval to 120 s increases, not decreases, latency.

D. SQS introduces queue polling latency; a consumer would still need to batch or long-poll messages, so sub-second delivery is not guaranteed.

1. Amazon Kinesis Data Firehose Developer Guide – “BufferingHints: … you can set IntervalInSeconds to 0 to disable buffering and have records delivered immediately.” https://docs.aws.amazon.com/firehose/latest/dev/create-destination.html#es-buffering

2. AWS Big Data Blog – “Design patterns for near-real-time analytics using Amazon Kinesis Data Firehose and Amazon OpenSearch Service” (section: ‘Reducing latency with zero-second buffering’). https://aws.amazon.com/blogs/big-data/design-patterns-for-near-real-time-analytics-using-amazon-kinesis-data-firehose-and-amazon-opensearch-service/