Temporal

Prerequisite: Part 8 of the System Design Masterclass. Read Part 7: Idempotent API Design first — compensating transactions in Saga must be idempotent. Answer-first: The Saga Pattern coordinates distributed transactions across microservices by decomposing a large transaction into a sequence of local transactions. If any step fails, the system automatically executes compensating transactions in reverse order to undo completed steps. Each local transaction must be idempotent. What Are the Problems with 2PC in Microservices? Answer-first: Two-Phase Commit (2PC) is a blocking protocol with a coordinator single point of failure. If the coordinator crashes between the Prepare and Commit phases, all participants are blocked indefinitely with locks held — a catastrophic failure mode in microservices. These are the same core banking distributed transaction challenges seen in legacy systems. ...

Answer-first: How banks replace monolithic cores (Temenos, Finacle) with composable banking using Go microservices, Saga orchestration, NewSQL ledgers, and Strangler Fig. Legacy core banking systems were designed in a different era. Temenos T24, Finacle, and Flexcube shared one defining assumption: the bank’s entire product catalogue — deposits, lending, payments, trade finance — would live inside a single, tightly coupled application and a single, shared database. That assumption held when banking moved at human speed. It breaks completely when product releases need to go from months to days, when a single fraud engine update must not risk a payments outage, and when engineers on a COBOL codebase are retiring faster than they can be replaced. ...

1. Introduction: Deconstructing the Legacy Core Answer-first: A modern banking microservices architecture replaces legacy monolithic ledgers (like T24 or Flexcube) using Go for high-throughput transaction routing. The system achieves distributed consistency without two-phase commit (2PC) by combining Event Sourcing (immutable ledger streams), Saga Orchestration (using Temporal or Dapr), the Transactional Outbox pattern, and PostgreSQL unique constraints for API idempotency. For decades, banks relied on monolithic core systems like Temenos T24 or Oracle FLEXCUBE. While robust, these systems present severe bottlenecks for modern digital banking. They were designed for overnight batch processing, not real-time, API-first global transactions. ...