Design a globally scaled frontend that sends events to a legacy streaming backend which requires strict chronological, non-duplicated processing. Which product combination provides guaranteed-once, FIFO delivery?

Cloud Pub/Sub provides at-least-once delivery, meaning messages might be duplicated. It also doesn't guarantee strict FIFO ordering across all subscribers in a globally scaled setup without additional mechanisms. Cloud Dataflow, with its streaming capabilities and stateful processing, can deduplicate messages and enforce strict ordering before sending them to the legacy backend. This combination ensures guaranteed-once, FIFO delivery. Cloud Pub/Sub alone cannot guarantee this. Stackdriver (now Cloud Logging and Cloud Monitoring) is for logging and monitoring, not data processing. Cloud SQL is a relational database, not a streaming processor for this use case.