Configuring Database Permissions for Log Access

In this lesson, you will learn how to configure the specific database-level privileges required to grant Change Data Capture (CDC) connectors read-only access to transaction logs.

To perform real-time data streaming, CDC connectors do not query your application tables directly; instead, they "tail" the database’s transaction logs (like Postgres WAL or MySQL Binlog). Because these logs contain the raw history of all database modifications, granting access to them is a sensitive operation. You must follow the principle of least privilege to ensure your streaming pipeline remains secure.

Configuring PostgreSQL for Logical Decoding

For PostgreSQL, the connector requires a user with REPLICATION privileges. This allows the connector to stream data changes from the Write-Ahead Log (WAL) without requiring superuser access.

You can create a dedicated user for your CDC service like this:

-- Create a dedicated role for the CDC connector
CREATE ROLE cdc_user WITH LOGIN PASSWORD 'secure_password';

-- Grant replication permission
ALTER ROLE cdc_user REPLICATION;

-- Ensure the user can read the necessary tables
GRANT CONNECT ON DATABASE inventory_db TO cdc_user;
GRANT USAGE ON SCHEMA public TO cdc_user;
GRANT SELECT ON ALL TABLES IN SCHEMA public TO cdc_user;

Essential Security Considerations

When setting up these permissions, keep three best practices in mind:

1. Isolation: Never use a database administrator or application-owner account for your CDC connector. Create a dedicated cdc_user specifically for the replication task.
2. Logical Decoding Slots: If you are using PostgreSQL, ensure your cdc_user has permission to manage replication slots. If the connector fails, these slots can grow and consume disk space, so monitoring the replication lag is vital.
3. Read-Only Constraints: By granting SELECT only on the tables being tracked, you prevent the connector from inadvertently performing data manipulation (DML) or administrative tasks on your source database.

By restricting the connector’s identity to only the roles necessary for log reading, you minimize the blast radius of a potential credential compromise while ensuring the streaming pipeline can reconstruct your data history reliably.

Key Takeaway: Secure log access requires creating a dedicated service account with explicit replication and read-only table privileges, ensuring the CDC process can extract transaction history without possessing unauthorized write or administrative capabilities.