cdc-debezium-rails

CDC with Debezium

CDC publishes every row change in your Rails DB as a Kafka event. Downstream consumers (search index, data warehouse, audit log, downstream services) get them without your app emitting anything. Powerful and dangerous — every Rails write becomes a public contract.

The opinion

Use Debezium with Postgres logical replication when you have multiple downstream consumers needing eventually-consistent DB state (search, warehouse, cache invalidation). Do NOT use CDC as your domain event bus — emit explicit domain events from the app layer for that. CDC leaks schema; domain events express intent. Set REPLICA IDENTITY FULL on tables you publish from. Use a single publication and replication slot per Debezium connector. Tombstone-handle deletes.

When CDC fits

The litmus test: would a column rename break downstream? If yes, you're using CDC for the wrong thing.

Postgres setup

-- postgresql.conf
wal_level = logical
max_replication_slots = 4      -- one per Debezium connector
max_wal_senders = 4

-- Restart Postgres.

-- Create a publication for the tables you want to stream
CREATE PUBLICATION rails_app_pub FOR TABLE posts, users, orders;

-- Or all tables (broad)
-- CREATE PUBLICATION rails_app_pub FOR ALL TABLES;

-- Critical: enables UPDATE/DELETE events to include the previous row state
ALTER TABLE posts REPLICA IDENTITY FULL;
ALTER TABLE users REPLICA IDENTITY FULL;
ALTER TABLE orders REPLICA IDENTITY FULL;

-- Replication user with limited grants
CREATE ROLE debezium WITH REPLICATION LOGIN PASSWORD 'redacted';
GRANT CONNECT ON DATABASE rails_app TO debezium;
GRANT USAGE ON SCHEMA public TO debezium;
GRANT SELECT ON ALL TABLES IN SCHEMA public TO debezium;
ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT SELECT ON TABLES TO debezium;