The need to move data from running databases to data warehouses or data lakes arrives endlessly. But you can't stop the operational database. Nightly full dumps scale explosively as data grows, and changes during the dump get missed. And "last night's snapshot" is useless for real-time analysis.
CDC (Change Data Capture) solves this. CDC says "don't re-read everything, capture only what changed since last time." In AWS, AWS Database Migration Service (DMS) handles this. Despite the name "Migration," it performs both one-time migration and ongoing replication via CDC.
DMS works as a combination of three parts. Understanding this decomposition solves half the exam questions.