Financial services require immutable audit, zero data loss, sub-second consistency. Pro design: DynamoDB Global Tables (multi-master), Secrets Manager rotation, GuardDuty + Security Hub org-wide, Backup Vault Compliance Lock Object Lock, regular FIS chaos tests, Aurora Global + DDB Global for critical ledgers.
Core: Compliance is non-negotiable → Security pillar first → Reliability second → Cost last. Regulators demand 7-year WORM logs, dual ledger reconciliation, and documented DR drills.