Migrating a Cloud SQL database from one Google Cloud project to another can be challenging—especially when you want minimal downtime and continuous replication (via Change Data Capture — CDC).
Google's Database Migration Service (DMS) makes this straightforward, even over public IP connectivity (ideal when VPC peering or Shared VPC isn't feasible).
In this guide, I walk you through a real-world cross-project migration of a Cloud SQL for MySQL instance using public IP allowlist connectivity — continuous mode — from source project → destination project.
This method helped me consolidate databases, refactor environments, and improve project isolation/security/governance.
High-level flow of DMS continuous migration with public IP connectivity
1. Introduction
Purpose
This post provides a detailed, production-tested step-by-step guide to migrate a Cloud SQL instance between GCP projects using DMS over public IP. It covers prerequisites, IAM roles, connectivity setup, job configuration, testing, cutover (promotion), and verification.
Target Audience
2. Overview
Database Migration Service (DMS) is a fully managed GCP service for zero/minimal-downtime migrations to Cloud SQL (MySQL, PostgreSQL) and AlloyDB.
Use cases for cross-project migration:
Consolidating scattered databases into a central project
Refactoring legacy/multi-project environments
Enforcing better security & governance through project boundaries
We use continuous migration (full load + CDC) over public IP allowlist connectivity.
Note: All DMS resources (connection profile, migration job, etc.) must reside in the same region as the destination Cloud SQL instance.
3. Prerequisites
| Tool / Technology |
Requirement |
| Google Cloud Platform |
Active billing in both projects |
| Cloud SQL |
Same engine & version (e.g. MySQL 8.0.35+) |
| Database Migration Service |
Enabled in the destination project |
Required IAM Roles
| Role |
Project |
Purpose |
Cloud SQL Admin (roles/cloudsql.admin) |
Both |
Manage Cloud SQL instances |
Database Migration Admin (roles/datamigration.admin) |
Destination |
Create & manage DMS jobs/profiles |
Compute Network Admin (roles/compute.networkAdmin) |
Destination |
Manage authorized networks (allowlist) |
4. Step-by-Step Migration Guide
Step 1: Get the Public IP of the Source Cloud SQL Instance
Go to SQL > Instances in the source project
Open the instance → Overview tab
Copy the Public IP address
Step 2: Create a Connection Profile in the Destination Project
Step 3: Create the Migration Job
Step 4: Define Source Configuration
Step 5: Define the Destination Cloud SQL Instance
Important: This choice (existing vs new) is permanent.
DMS requires bidirectional connectivity over public IP.
Destination instance:
Go to Cloud SQL > Connections
Enable Public IP if not already
Note the Outgoing IP from Overview tab (this is the IP DMS uses to connect to source)
Source instance:
Step 7: Test the Migration Job
In the migration job creation wizard → Test button
Wait for "Test run complete – successful"
If it fails: double-check credentials, public IPs, allowlist, firewall rules
Once passed → Create (you can start immediately or later)
Step 8: Start & Monitor the Job and Verify Data Consistency
Source :
Destination :
After the verification of data consistency, Once the replication delay is least, proceed with promoting the destination Database to be a writeable instance.
Step 10: Check Migration Job Logs or Destination Instance Logs
If the logs for the migration job or the destination instance logs are required, they can be viewed by clicking on the view logs and selecting the logs which are required.
5. Troubleshooting
5.1 : Common Issues
| Issues |
Possible Cause |
| Connection Test Fails |
Public IP not whitelisted or wrong Credentials |
| Version Mismatch |
Cloud SQL minor version mismatch |
| IAM Permission errors |
Missing roles in source/destination |
| Cutover Fails |
Replication lag or write operations on source. |
5.2 : Solutions
Re-check authorized network setting
Verify SQL Version via gcloud sql instance describe
Ensure IAM Roles and API's are correctly configured
6. Conclusion
This blog explained how to migrate a Cloud SQL instance across GCP Projects using DMS over public IP.
It covered :
API Setup
Source/Destination Configuration
DMS Connection profiles and job creation
Troubleshooting the issues
