Amazon Web Services (AWS) Database Migration Service (DMS) is a cloud-based service that facilitates the migration of databases to and from AWS. It helps organizations migrate their databases to AWS easily and securely, minimizing downtime during the migration process. AWS DMS supports a wide variety of database engines, making it a versatile tool for database migrations.

This knowledge base provides a detailed overview of AWS DMS migration tasks, including their configuration, operation, best practices, and troubleshooting.

Understanding AWS DMS Migration Tasks

What are Migration Tasks?

In the context of AWS DMS, a migration task is a set of actions that define how data is moved from a source database to a target database. Migration tasks can be used for:

• Full Load: Migrating all data from the source database to the target database.
• Change Data Capture (CDC): Capturing ongoing changes from the source database and applying them to the target database in real-time. This feature is essential for minimizing downtime during the migration process.
• Full Load plus CDC: A combination of both full load and ongoing data capture, allowing for a seamless migration experience.

Key Components of Migration Tasks

Several key components are involved in configuring and managing AWS DMS migration tasks:

• Replication Instance: This is a server that runs the AWS DMS software and performs the data migration. It manages data replication and the execution of migration tasks.

• Source Endpoint: This defines the connection details to the source database. It includes the database engine type, server name, database name, and credentials.

• Target Endpoint: This specifies the connection details to the target database, similar to the source endpoint.

• Migration Task Settings: These settings determine how the migration task operates, including options for full load, CDC, and error handling.

• CloudWatch Metrics: AWS DMS integrates with Amazon CloudWatch, allowing you to monitor migration tasks in real-time. You can track metrics such as task status, data transfer rates, and error rates.

Creating Migration Tasks

Prerequisites for Creating Migration Tasks

Before you can create a migration task, ensure that you have completed the following prerequisites:

• AWS Account: You need an active AWS account with appropriate permissions to access AWS DMS.

• Replication Instance: A replication instance must be created. This instance handles the data transfer and should have sufficient resources (CPU, memory, and storage) based on the expected workload.

• Source and Target Endpoints: Define the source and target endpoints in AWS DMS. Ensure you have connectivity to both databases.

Steps to Create a Migration Task

Creating a migration task involves several steps:

1. Open the AWS DMS Console: Log in to the AWS Management Console and navigate to the AWS Database Migration Service console.

2. Select the Replication Instance: Choose the replication instance you want to use for the migration task.

3. Create the Migration Task:

   • Click on Tasks in the left navigation pane.
   • Click on the Create Task button.
   • Provide a name for the migration task and select the migration type (e.g., Full Load, CDC, or both).

4. Specify Source and Target Endpoints: Choose the previously configured source and target endpoints for the task.

5. Configure Migration Task Settings: Configure the task settings, including:

   • Table Mapping: Define which tables and schemas should be included in the migration.
   • Transformation Rules: Apply any transformation rules, such as changing data types or renaming columns.
   • Error Handling: Specify how errors should be handled during the migration.

6. Review and Create: Review the task configuration and click Create Task to initiate the migration.

Table Mapping and Transformation Rules

Table Mapping allows you to specify which tables in the source database will be migrated to the target database. You can choose to include all tables or selectively include specific tables based on your requirements.

Transformation Rules enable you to modify the data during migration. For example, you might want to:

• Rename tables or columns.
• Change data types (e.g., converting a VARCHAR to INT).
• Filter rows based on specific criteria.

These rules can be defined using JSON format within the migration task configuration.

Running Migration Tasks

Starting the Migration Task

After creating the migration task, you can start it:

1. Select the Task: In the AWS DMS console, navigate to the Tasks section and select the task you created.
2. Start the Task: Click on the Start button to initiate the migration process.

Monitoring Migration Tasks

Monitoring the status of migration tasks is crucial for ensuring successful data migration. AWS DMS provides several monitoring options:

• Task Status: The task status can be viewed in the AWS DMS console. Possible statuses include:

  • Ready: The task is configured and ready to run.
  • Running: The task is currently executing.
  • Failed: The task encountered an error and has stopped.
  • Stopped: The task was manually stopped.

• CloudWatch Metrics: AWS DMS integrates with Amazon CloudWatch, allowing you to track various metrics, such as:

  • Data transferred (bytes per second).
  • Task latency.
  • Number of rows processed.
  • Error counts.

Handling Errors

Errors can occur during migration tasks due to various reasons, such as connection issues, schema mismatches, or data type conflicts. AWS DMS provides mechanisms to handle errors:

• Error Handling Options: In the migration task settings, you can configure options for handling errors. This may include:

  • Log Errors: Choose to log errors for review.
  • Skip Errors: Specify how many errors to skip before stopping the task.

• Viewing Error Logs: Errors encountered during the migration can be viewed in the AWS DMS console under the Logs section of the migration task. You can also access detailed logs via Amazon CloudWatch.

Best Practices for Using AWS DMS Migration Tasks

1. Use Replication Instances Wisely: Choose an appropriately sized replication instance based on your data volume and migration speed requirements. Consider using a larger instance for large data migrations.

2. Plan for Downtime: If you are migrating a production database, plan the migration to minimize downtime. Utilize Change Data Capture (CDC) to capture changes after the full load to keep the target database in sync.

3. Test the Migration: Conduct a test migration before the actual migration to identify any potential issues. This will help you refine your table mappings and transformation rules.

4. Monitor Performance: Regularly monitor the migration task’s performance through the AWS DMS console and CloudWatch metrics. This helps identify bottlenecks or issues early.

5. Optimize Table Mapping: Keep your table mapping as simple as possible. Exclude unnecessary tables to reduce migration time and complexity.

6. Utilize VPC Endpoints: For added security, consider using Amazon VPC endpoints to connect your source and target databases, especially when migrating databases hosted in Amazon RDS or EC2 instances.

Advanced Features of AWS DMS Migration Tasks

Data Transformation

AWS DMS supports basic data transformations during migration. You can modify data on the fly, making it possible to convert data types, change values, or filter rows as they are migrated.

Support for Multiple Sources and Target Endpoints

AWS DMS allows you to configure multiple source and target endpoints, enabling complex migration scenarios. For instance, you can migrate data from multiple databases to a single target or from a single source to multiple targets.

Ongoing Replication

With the CDC feature, AWS DMS can continuously replicate changes from the source database to the target database. This is particularly useful for maintaining data synchronization in real-time applications.

Integration with AWS Services

AWS DMS integrates seamlessly with various AWS services, allowing you to enhance your migration workflows. For example:

• Amazon S3: Use S3 as a staging area during migration.
• Amazon CloudWatch: Monitor migration tasks and set up alerts for specific events.
• AWS Lambda: Trigger Lambda functions based on migration events or changes.

Troubleshooting AWS DMS Migration Tasks

Common Issues and Solutions

During migration, you may encounter several common issues. Here are some potential problems and their solutions:

• Connection Issues: If your migration task cannot connect to the source or target database, check the endpoint configuration for accuracy. Ensure that network security groups allow traffic from the replication instance.

• Schema Mismatches: If there are schema mismatches between the source and target databases, ensure that the data types and structures are compatible. Review the table mapping and transformation rules for accuracy.

• High Latency or Slow Performance: If the migration task experiences high latency, consider resizing the replication instance or optimizing the task settings. Monitor CloudWatch metrics for insights.

Using Logs for Troubleshooting

AWS DMS provides detailed logs that can help diagnose issues during migration:

• Task Logs: These logs contain information about task execution and any errors encountered. You can access them through the AWS DMS console or CloudWatch.

• Replication Instance Logs: Logs for the replication instance can provide insights into connectivity issues or performance bottlenecks.