From On-Premises to AWS: The Ultimate Guide to Database Migration Service

The Ultimate Guide to Database Migration Service

Migrating databases is a complex and challenging process for many organizations. One major issue is the difficulty in capturing and migrating crucial functions and stored procedures that ensure the correct operation of both the database and its associated applications. This task becomes even more complicated when databases need to be refactored, such as transitioning from on-premises systems like MS SQL to AWS’s Aurora MySQL. 

Achieving lossless data transfer and synchronization is another significant challenge, especially for databases that need to remain operational continuously. The volatility of database I/O can further complicate maintaining consistency and integrity during the migration process. These issues underscore the need for effective tools and strategies to manage database migrations. 

In this article, we will explore Database Migration Service (DMS), which is designed to tackle these migration challenges. We will discuss the features and benefits of DMS, highlighting tools offered by AWS to facilitate seamless and efficient database migrations. Understanding DMS can help organizations navigate the complexities of database migration with minimal downtime and data loss. 

What is Database Migration Service?

Database Migration Service (DMS) are specialized tools and platforms designed to facilitate the transfer of databases from one environment to another. This process can involve migrating databases between different physical locations, types, or versions, such as moving from an on-premises database to a cloud-based solution or switching from one database vendor to another. The primary goal of DMS is to ensure a smooth transition with minimal downtime, preserving data integrity and application functionality throughout the migration process. 

These services typically encompass several critical components, including data migration, schema migration, and application migration. Data migration involves the actual transfer of data from the source to the target database, while schema migration replicates the structure and metadata of the source database in the target system. Application migration ensures that any applications relying on the database continue to function correctly after the migration. Key features of DMS include data transformation to match the target schema, data validation to ensure accuracy, and strategies to minimize downtime during the migration. 

To address these challenges, we leverage two main AWS migration services: AWS Schema Conversion Tool (SCT) and AWS Database Migration Service (DMS). These tools offer automated solutions for assessing the source database, converting schemas, transferring data, and validating the migration, thereby simplifying the complex process of moving databases. By utilizing these services, organizations can modernize their IT infrastructure, improve performance, reduce costs, and seamlessly adopt cloud technologies. 

What is AWS Database Migration Service?

AWS Database Migration Service (DMS) facilitates the quick and secure migration of databases to AWS with minimal downtime. It supports both homogeneous migrations, such as Oracle to Oracle, MySQL to MySQL, etc., and heterogeneous migrations between different database engines, such as Microsoft SQL Server to Amazon Aurora, etc. 

Without using tools like DMS, migrating a relational database like MS SQL or MySQL would require a set of steps similar to: 

  1. Identify or create a read replica 
  2. Perform a static SQL dump (from the read replica) 
  3. Import the static SQL dump on the target database 


This process is simple. However, in situations with highly volatile data (high write activity), the target data may be outdated even before the SQL dump is restored on the target database. Repeating the static dump method will not resolve this, regardless of how many times you perform it. For this reason, database administrators (DBAs) typically perform data migrations within safe maintenance windows, typically in the early morning hours. 

DMS operates differently by offering dynamic data migration. It maintains two active DB connections – one to the source and the other to the target – and conducts an ongoing real-time synchronization of data from the source to the target. 

Deltas are automatically performed, allowing you to sync to the target from a hot DB’s read replica, conduct A/B testing on both systems in parallel if desired, and then switch over to the target DB. After a nominal period – to allow read replication to propagate to the target – you simply disable DMS and conclude the data migration process. In most cases, there is zero downtime during the switchover, although this will depend on how your application’s traffic is routed. 

Here’s how AWS DMS replication process illustrates in diagram: 

AWS Database Migration Services


About AWS Schema Conversion Tool (AWS SCT)  

AWS Schema Conversion Tool (SCT) is utilized to convert your database schema from the source database (e.g., on-premises) to the target database (AWS). SCT supports OLTP conversions, data warehouse conversions, and NoSQL database conversions. 

SCT serves two primary use cases: 

  • Homogeneous Migrations 

These occur when the source database platform is the same as the target database platform. For instance, migrating from an on-premises MySQL database to a MySQL database in AWS. SCT automatically converts the source database schema and most database code objects – including views, stored procedures, and functions – to a format compatible with the target database. It can also identify objects that cannot be converted automatically, enabling manual intervention. This ensures that the target database’s schema closely resembles the source, minimizing post-migration errors. 

  • Heterogeneous Migration 

These occur when the source database platform differs from the target database platform. For instance, migrating from an on-premises MS SQL database to a PostgreSQL database in AWS. As implied by the name, the Schema Conversion Tool can dynamically convert schemas between database engines. This capability is particularly valuable when migrating and updating legacy systems to AWS. 

AWS Schema Conversion Tool vs Database Migration Service

When comparing AWS Schema Conversion Tool (SCT) to Database Migration Service (DMS), it’s like evaluating two indispensable tools in a craftsman’s toolbox. 

AWS Schema Conversion Tool (SCT) resembles a precision instrument, meticulously converting database schemas and code for seamless integration into AWS infrastructure. It streamlines the often-complex process of converting database elements, such as schemas, stored procedures, and functions, ensuring compatibility with AWS databases. Its capability to assess the source database’s complexity and generate comprehensive reports facilitates informed decision-making during migration planning. 

On the other hand, Database Migration Service (DMS) functions as the sturdy workhorse, tirelessly transferring data from source to target databases with minimal downtime. It provides a reliable mechanism for continuous data replication, ensuring data integrity throughout the migration process. With support for heterogeneous migrations and real-time data replication, DMS offers versatility and reliability, making it an essential component of any database migration strategy. 

In summary, while SCT excels in schema conversion and assessment, DMS shines in data migration and replication. Together, they form a powerful duo, enabling smooth and efficient database migrations to AWS infrastructure. 

AWS SCT Features

The AWS Schema Conversion Tool (SCT) is designed to simplify the process of converting database schemas and code for different database engines. Key features of AWS SCT include: 

Schema Conversion  

Automatically converts database schemas from source databases to target AWS databases. 

Code Conversion

Converts database code, including views, stored procedures, and functions, to a format compatible with the target database. 

Assessment Reports

Provides detailed reports on the complexity and compatibility of the source database with the target AWS database. 

Data Migration

Integrates with AWS DMS to facilitate data migration after schema conversion. 

Support for Multiple Databases

Supports a wide range of databases including Oracle, Microsoft SQL Server, MySQL, PostgreSQL, and others. 

AWS SCT Benefit

The AWS Schema Conversion Tool offers several benefits that streamline the database migration process: 


Automates the complex and time-consuming process of schema and code conversion, reducing manual effort and errors. 

Comprehensive Assessment

Delivers detailed assessment reports that help in understanding the scope and potential issues of the migration, enabling better planning and risk management. 

Cost Savings

Reduces the need for extensive manual intervention and specialized skills, leading to cost savings in migration projects. 

Integration with AWS DMS

Works seamlessly with AWS Database Migration Service to handle data migration, ensuring a cohesive and efficient migration process. 

Wide Compatibility

Supports multiple source and target databases, making it versatile for various migration scenarios. 

In summary, AWS SCT and AWS DMS together provide a robust solution for migrating databases to AWS, addressing both schema conversion and data migration needs. Understanding their features and benefits can help organizations effectively plan and execute their database migration projects. 

Explore the Convenience of Accessing AWS SCT and AWS DMS on CTM

As an authorized partner of AWS, Computrade Technology Malaysia (CTM) helps you avoid trial and error by providing support from consultation to deployment, maintenance, and after-sales support. Backed by a team of experienced and certified IT professionals, CTM guides you through the entire AWS solution adoption process for all your business data needs. 

Ready to take control of your database migration? Don’t wait any longer! Get a free consultation with our experts today. Discover how the AWS Schema Conversion Tool and Database Migration Service can simplify your database migration and optimize performance by clicking the link. 

Author: Ary Adianto
Content Writer CTI Group 

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