Concurrency-safe bid ingestion, deterministic settlement, and idempotent payment orchestration.
Bid ordering
PostgreSQL compare-and-set persistence is authoritative when multiple application instances accept bids concurrently.
Atomic history
The accepted bid and its immutable history row commit in the same transaction.
Reliable events
Settlement writes the order and pending outbox event together, making publication recoverable after a restart.
Payment safety
SQS is at-least-once delivery; durable idempotency claims prevent duplicate gateway authorization.
Credential boundary
Payment methods retain provider-issued instrument references only. Raw card data stays outside this service.
Observability
Actuator and Prometheus expose bounded business metrics without putting customer or payment IDs in metric tags.