How we reliably send a million messages per request: A Temporal Workflow deep dive

Parth Nagori (Staff Software Engineer, Twilio) traces the real architecture evolution of Twilio's million-recipient messaging system on Temporal, from child workflows generating tens of thousands of actions, to heartbeat-checkpointed long-running activities, to a sliding window pattern that parallelizes work across the fleet. He covers the operational surprises, entity workflows for concurrent mutations, and the Temporal primitives (fairness keys, StartDelay, workflow ID dedup) that replaced infrastructure they thought they needed to build themselves.