If we have an RDS instance as the source and we decide not to use DMS due to cost concerns, how can we capture CDC data from the RDS instance?

For MySQL or MariaDB RDS, enable the binary log (binlog) and set the log_bin_trust_function_creators parameter. Once binlog is on, you can use MySQL’s built‑in replication protocol to stream changes. A lightweight approach is to run a custom script that connects to the binlog using the MySQL Connector/NET or Python’s mysql-replication library, parses the binlog events, and writes them to a target system or a message queue. For PostgreSQL RDS, enable logical replication by setting wal_level to logical and creating a publication. A consumer can connect via the logical replication protocol to receive INSERT/UPDATE/DELETE changes. These methods avoid the DMS licensing cost and give you fine‑grained control, but they require you to manage the replication slots, handle failures, and ensure the consumer keeps up. If you prefer managed services, you could use AWS Database Migration Service’s free tier for small workloads, or use AWS Glue or Kinesis Data Streams with a custom connector to read the binlog. Each option trades off cost, complexity, and operational overhead.