Migrating an Amazon RDS DB Instance to Another VPC in the Same AWS Account

Prerequisites

• Administrative access to the AWS Management Console or AWS CLI with appropriate IAM permissions for RDS, VPC, and EC2.
• Source and target VPCs configured in the same AWS account and region.
• A running RDS DB instance in the source VPC.
• Backup of the RDS instance (manual or automated snapshot) for safety.
• Sufficient storage and compute capacity in the target VPC for the new DB instance.
• AWS CLI installed and configured (optional, for CLI-based steps).
• Knowledge of the application connecting to the RDS instance to update connection strings post-migration.

Migration Overview

1. Create a snapshot of the source RDS DB instance.
2. Restore the snapshot to a new RDS DB instance in the target VPC.
3. Configure the new DB instance (security groups, subnets, etc.).
4. Update application connection strings.
5. Verify the migration and clean up.

Step 1: Create a Snapshot of the Source RDS DB Instance

1. Log in to the AWS Management Console and navigate to the RDS service.
2. Select the DB instance you want to migrate.
3. Choose Actions > Take snapshot.
4. Provide a name for the snapshot (e.g., source-db-snapshot-2025) and click Take Snapshot.
5. Wait for the snapshot status to change to Available (this may take a few minutes depending on the database size).

Step 2: Restore the Snapshot to a New RDS DB Instance in the Target VPC

1. In the RDS console, navigate to Snapshots and select the snapshot created.
2. Choose Actions > Restore snapshot.
3. Configure the new DB instance:
   • DB instance identifier: Provide a unique name (e.g., target-db-instance).
   • VPC: Select the target VPC from the dropdown.
   • Subnet group: Choose a DB subnet group associated with the target VPC. Ensure the subnet group includes subnets in at least two Availability Zones.
   • Security group: Assign a security group in the target VPC that allows inbound traffic on the database port (e.g., 3306 for MySQL).
   • Other settings: Match the source DB instance’s settings (e.g., instance type, storage, parameter group) or adjust as needed.
4. Click Restore DB instance.
5. Wait for the new DB instance to reach the Available status.

Step 3: Configure the New DB Instance

1. Verify connectivity: Ensure the new DB instance is accessible from your application or a test client (e.g., using mysql or psql).
2. Update security groups: Confirm that the security group rules allow traffic from application servers or other resources in the target VPC.
3. Parameter group: If the source DB instance uses a custom parameter group, assign a similar one to the new instance and apply any necessary changes.
4. Option group: Assign the appropriate option group if the source instance uses specific options (e.g., Oracle auditing).
5. Enable backups and maintenance: Configure automated backups and maintenance windows to match the source instance.

Step 4: Update Application Connection Strings

1. Obtain the endpoint of the new DB instance from the RDS console (e.g., target-db-instance.xxxxxxxxxxxx.us-east-1.r..).
2. Update your application’s configuration to use the new endpoint. This may involve:
   • Modifying environment variables.
   • Updating configuration files (e.g., database.yml for Rails apps).
   • Redeploying the application.
3. Test the application to ensure it connects to the new DB instance without issues.

Step 5: Verify the Migration and Clean Up

1. Verify data integrity: Run queries or tests to confirm that the data in the new DB instance matches the source.
2. Monitor performance: Check CloudWatch metrics for the new DB instance to ensure it performs as expected.
3. Decommission the source DB instance:
   • Stop application traffic to the source DB instance.
   • Take a final snapshot for backup purposes.
   • Delete the source DB instance to avoid unnecessary costs.
4. Delete the temporary snapshot if no longer needed.

Minimizing Downtime

• Read replica approach: Create a read replica of the source DB instance in the target VPC, promote it to a standalone instance, and then update the application. This requires additional configuration and may not be supported for all RDS engines.
• DNS update: Use a CNAME record to point to the new DB instance’s endpoint and update the DNS record instead of changing application code. Ensure the TTL is low to minimize propagation delays.
• Pre-warming: Run test queries on the new DB instance to warm up the buffer pool before switching traffic.

Troubleshooting

• Connectivity issues: Verify security group rules, route tables, and NACLs in the target VPC.
• Performance degradation: Check if the new instance type or storage configuration matches the source.
• Snapshot restore errors: Ensure the snapshot is compatible with the target DB engine version and that the target VPC has sufficient resources.

Conclusion