Durable Execution — Payment Workflow Replay Diagram

Workflow as a Task Graph

One business transaction spans several services: fraud check, card debit, bank deposit
An orchestrator schedules tasks; executors run them on some machine
Each completed step is appended to a durable log before the next starts

Failure Without a Transaction

The steps cannot be wrapped in one database transaction across services
A crash after charging the card must not leave the deposit undone
Third-party APIs must be idempotent and called with unique IDs

Replay Semantics

Re-execution skips steps already recorded and returns their previous results
Determinism is required: same inputs must produce the same calls in the same order
Code changes deploy as new versions so old invocations keep replaying old logic