Database Migration Service

Database Migration Service (DMS) is Google Cloud's fully managed service for migrating databases to GCP with minimal downtime. It supports continuous replication from source databases to Cloud SQL, AlloyDB, and Cloud Spanner, enabling a smooth transition from on-premises, other clouds, or self-managed instances.

---

What Is Database Migration Service?

DMS provides a serverless, end-to-end migration pipeline that:

• Continuously replicates data from source to destination in near real-time.
• Minimises downtime — applications continue running during migration; you cut over when replication is caught up.
• Handles schema conversion — for heterogeneous migrations (e.g. Oracle to PostgreSQL), DMS includes schema mapping tools.
• Validates data — built-in validation ensures data integrity before and after cutover.
• Fully managed — no servers to provision or manage.

---

Supported Migration Paths

Homogeneous Migrations (Same Engine)

Source	Destination
MySQL (on-premises, AWS RDS, Azure)	Cloud SQL for MySQL
PostgreSQL (on-premises, AWS RDS, Azure)	Cloud SQL for PostgreSQL
PostgreSQL	AlloyDB for PostgreSQL

Heterogeneous Migrations (Different Engine)

Source	Destination
Oracle	Cloud SQL for PostgreSQL, AlloyDB
SQL Server	Cloud SQL for PostgreSQL

Heterogeneous migrations require schema and data type conversion, which DMS assists with using the integrated Ora2Pg (for Oracle) and conversion workspace tools.

---

Migration Workflow

Step 1: Create a Connection Profile

Define the source and destination databases:

• Source — connection details (host, port, credentials, SSL).
• Destination — Cloud SQL instance, AlloyDB cluster, or Spanner database.

Step 2: Create a Migration Job

Configure the migration:

• Migration type — one-time (full dump and load) or continuous (CDC with ongoing replication).
• Database selection — choose specific databases or all databases.
• Connectivity — VPC peering, VPN, or reverse SSH tunnel for secure access to the source.

Step 3: Test the Migration

DMS runs pre-flight checks to validate:

• Network connectivity between source and destination.
• Source database configuration (e.g. binary logging enabled for MySQL, logical replication for PostgreSQL).
• User permissions.
• Schema compatibility.

Step 4: Start the Migration