Events for each bank account must be processed in order, but the total volume needs hundreds of consumers. What do you do?

Options

• ✗ Use a single consumer for everything
• ✓ Partition by account id, so each account's events go to one partition or message group, handled in order Correct
• ✗ Let consumers sort events by timestamp after reading
• ✗ Give up ordering and process events in parallel

Why

Ordering only matters within an account, so you get order there and parallelism across accounts. Kafka partition keys and SQS FIFO message groups both work this way.

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