This comprehensive guide details the process of migrating a MySQL database running on Amazon RDS to another RDS MySQL instance using AWS Database Migration Service (DMS). We'll cover setting up the environment, configuring DMS, troubleshooting common issues, and best practices for a smooth and efficient migration. This tutorial focuses on an RDS-to-RDS migration for simplicity, but the principles apply to other scenarios, including on-premise to AWS migrations. We will be using the Thailand region for this example.
Prerequisites and Setup
Before starting, ensure you have the following:
Two Amazon RDS MySQL instances: One source and one target. The database versions must be compatible with DMS. Always consult the official AWS documentation for the latest compatibility information. You can find comprehensive instructions on creating and configuring RDS instances in this helpful resource: https://dev.classmethod.jp/articles/how-to-create-rds-and-connect-from-ec2/
AWS Account: With appropriate permissions to create and manage DMS resources.
VPC Configuration: Both RDS instances should reside within the same Virtual Private Cloud (VPC). For enhanced security, disable public accessibility on your RDS instances. Public accessibility incurs additional costs and introduces unnecessary security risks.
Replication Subnet Group (optional but recommended): If you don't already have one, create a Replication Subnet Group within your VPC. This subnet group should include the same subnets used by your RDS instances. This ensures optimal network connectivity during the migration process. Locate this under the DMS service in the AWS Management Console.
IAM Role: Create an IAM role with appropriate permissions for DMS to access your S3 bucket (required for Premigration Assessment). The necessary permissions are detailed in the AWS documentation: https://docs.aws.amazon.com/dms/latest/userguide/CHAP_Tasks.AssessmentReport.Prerequisites.html
S3 Bucket: Create an S3 bucket to store the Premigration Assessment report. This report provides valuable insights into potential compatibility issues before the migration begins.
Creating the Replication Instance
The Replication Instance is the engine that drives the migration process. This is a dedicated EC2 instance managed by DMS. Configure this instance with appropriate resources based on your data volume and desired performance. Choose an instance size that can handle the load of your database migration. Ensure the instance is in the same VPC as your RDS instances and has appropriate network access.
Setting Up Endpoints
Endpoints define the connection parameters for both the source and target databases. You will need to create two endpoints:
Source Endpoint: This endpoint represents the source MySQL RDS instance from which you're migrating data. Specify the host, port, database name, username, and password for your source RDS instance.
Target Endpoint: This endpoint represents the target MySQL RDS instance where the data will be migrated. Specify the host, port, database name, username, and password for your target RDS instance.
After creating the endpoints, test the connection to ensure proper connectivity and authentication. If you encounter connection issues, verify your security group configurations, usernames, and passwords.
Creating the Database Migration Task
This step defines the specifics of the migration. Navigate to the DMS console and create a new Database Migration Task. Provide a descriptive name for your task (e.g., Migrate-Sampledb). Select the replication instance you created earlier and specify both your source and target endpoints.
Selection Rules
This crucial step defines which tables and schemas to migrate. Use the "Add New Selection Rule" option to define criteria. For instance, to migrate all tables from a specific schema:
schema name is like 'sampledb' and Source table name is like '%'
To migrate all tables from all schemas, use:
schema name is like '%' and Source table name is like '%'
Adjust these rules to precisely select the data you want to migrate.
Task Settings: Optimizing for Success
Configure the following settings to ensure a smooth migration:
Data Validation: Enable this option to compare data in the source and target databases after the migration. This validates the accuracy of the process.
Task Logs (CloudWatch Logs): Enable this to monitor the migration progress and troubleshoot potential issues. Detailed logs are invaluable during troubleshooting.
Premigration Assessment: Enabling this feature performs a thorough assessment of your schemas, data types, and constraints for compatibility issues. This identifies potential problems before the migration begins, saving you significant time and effort later. This assessment requires an S3 bucket for storing the report.
Once all settings are configured, click "Create Database Migration Task".
Troubleshooting Common Issues
The Premigration Assessment is your first line of defense against issues. If you encounter failures, refer to the detailed assessment report. Common issues and their solutions include:
Connection Timeouts
DMS might experience connection timeouts if the network latency between the replication instance and the RDS instances is high, or if the RDS instances' connection timeout settings are too low. Increase the wait_timeout and interactive_timeout parameters in the RDS parameter groups for both the source and target instances. A value of at least 300 seconds is recommended. You might need to create custom parameter groups and apply them to your RDS instances, instead of using the default ones. Refer to the following resources:
- Modifying RDS Parameter Groups: https://dev.classmethod.jp/articles/setting-up-timezone-with-rds/
- AWS DMS MySQL Target Endpoint Configuration: https://docs.aws.amazon.com/dms/latest/userguide/CHAP_Target.MySQL.html
Insufficient Privileges
The DMS user might lack the necessary privileges on the source or target databases. Connect to both databases and grant the DMS user the appropriate privileges. The specific privileges required depend on the operations being performed. Always follow the AWS documentation for minimum privilege requirements:
- AWS DMS MySQL Source Endpoint Configuration: https://docs.aws.amazon.com/dms/latest/userguide/CHAP_Source.MySQL.html
Remember to replace placeholders like 'DMS_USER', 'Strongpassword123!', and 'your_database_name' with your actual credentials and database name.
Granting excessive privileges is a security risk. Therefore, granting only the necessary minimum privileges is highly recommended.
Starting and Monitoring the Migration
After addressing any premigration issues, start the migration task by selecting "Restart/Resume" from the Actions menu. Monitor the progress in CloudWatch Logs.
If the migration process encounters errors, thoroughly analyze the CloudWatch Logs for detailed error messages. These logs provide crucial insights into the nature of the problems encountered.
Post-Migration Validation
After the migration completes, verify the data integrity. Compare the data in the source and target databases. Data validation, if enabled, will automatically perform this comparison.
Cleaning Up Resources
After a successful migration, delete all unnecessary resources to avoid incurring unnecessary costs. This includes the replication instance, endpoints, and the migration task. You can also delete the RDS instances you created for the migration. Consult the following resource for guidance on deleting RDS instances: https://dev.classmethod.jp/articles/how-to-create-rds-and-connect-from-ec2/#toc--rds1
Best Practices and Advanced Techniques
Testing: Always perform a test migration before migrating production data. This allows you to identify and resolve potential issues in a safe environment.
Incremental Migrations: For large databases, consider incremental migrations to minimize downtime.
Schema Conversion Tool (SCT): For complex scenarios or heterogeneous migrations (migrating between different database systems), leverage the AWS Schema Conversion Tool (SCT): https://docs.aws.amazon.com/SchemaConversionTool/latest/userguide/CHAP_Welcome.html
By following these steps and best practices, you can efficiently and reliably migrate your MySQL databases using AWS DMS. Remember to consult the official AWS documentation for the most up-to-date information and best practices. Always prioritize security and data integrity throughout the migration process.