A synchronous chain makes one service wait for the next. A queue can absorb bursts and let a consumer work at its own pace, but now you must design retries, ordering, duplicates, and failed messages. A topic can fan an event out to independent consumers. Neither mechanism removes the need to know when a business operation has completed.
Caching reduces repeated work at the cost of possible staleness and invalidation complexity. Serverless services reduce some infrastructure management, but they still have limits, permissions, concurrency, and downstream dependencies. Choose these patterns because they fit a requirement, not because a diagram uses fewer boxes. The edge scenario involves a retry after a partial success: the consumer must preserve one business outcome despite multiple attempts.