For a requirement focused on synchronizing record updates from Salesforce to an external system in an event-driven and asynchronous manner, Change Data Capture (CDC) is the architecturally preferred solution over custom Platform Events.

CDC is designed specifically for data replication and synchronization. It automatically publishes change events for Salesforce records (Create, Update, Delete, and Undelete) to the event bus. Unlike Platform Events, which require manual publishing via Apex triggers or Flows, CDC is a low-code feature that requires only a simple activation for the Contact object in Setup. The external homegrown application can then act as a CometD subscriber, listening to the specialized /data/ContactChangeEvent channel to receive near real-time updates without the need for constant polling. Furthermore, CDC provides ordered, replayable events and an extended 72-hour retention window, ensuring that the homegrown application can recover missed updates using a Replay ID if it momentarily loses connection. This native broadcasting capability ensures data integrity across systems while breaking the tight coupling between Salesforce and the legacy application.