An Overview of AWS DMS – Function, Benefits and Limitations

A cloud-based service, AWS DMS (Amazon Web Service Database Migration Service) is optimized for migrating relational databases, data warehouses, NoSQL databases, and more to AWS. You can migrate databases from on-premises servers to the cloud or from one cloud provider to another.

One of the main reasons why AWS DMS is a preferred service for database migration is its ability to keep the migration process running even when the source database is fully functional. This does away with the need for downtime, a huge advantage for large data-driven organizations that would face operational problems if databases were to be shut down for any length of time. Further, you can also consolidate several databases into one petabyte-sized one with AWS DMS.

Functioning of AWS DMS

A basic definition of AWS DMS is that it is a service that operates as a replication software in the cloud. For database migration, your first task is to create a link between the source and the target database so that AWS DMS knows from where to move the data and to which location. The next stage is to define a task that moves the data to the target. AWS DMS auto handles migration even if the keys and tables required for migration are not available in the target database. However, you have the option to create the target tables or take the help of the AWS SCT (AWS Schema Conversion Tool) to build target tables, indexes, views, triggers, and more. 

You can either perform one-time database migration or replicate incremental changes at the source database continually to the target database. But in the second instance, you have to ensure that the two databases are always in sync. For migrating to a different database engine, you have to use the AWS SCT to convert the data codes and the schema structure of the source database to match that of the target database, a process that is followed during heterogeneous database migration with AWS DMS. 

Since AWS DMS is a vital component of the AWS Cloud, you get all the cutting-edge advantages of the cloud-like security, performance, cost-efficiency, and flexibility associated with the cloud.  

Benefits of AWS Database Migration Service

AWS DMS offers several benefits that enable easy and seamless database migration.

• User-friendly: In traditional migration methods, users had to face complex processes like installing and administering additional hardware and software and testing and debugging existing systems. Now, AWS DMS deploys, manages, and monitors all infrastructure that is used for migration. After the AWS DMS is configured, migration can be started within minutes.
• Scalability: Since AWS DMS operates in the cloud, users get access to unlimited storage facilities. If more resources are used for migration, it can be immediately downloaded from the cloud. Importantly, you pay only for the quantum of storage resources used without any flat fees or up-front charges as in older methods. Thus, database migration with AWS DMS is a very cost-effective option.
• Complete setup management: AWS DMSsupports and manages the complete infrastructure needed for database migration including error reporting, software patching, and monitoring the required hardware and software.
• Automatic failover: Automatic failover and reversal are critical benefits of AWS DMS. If there is an outage or the primary server is disrupted for any reason, secondary servers within the region or even in remote locations are automatically triggered and migration goes on without a break. When the issue is resolved, the primary server is updated immediately with all the changes that occurred in the break period and restarted. Hence, there is no data loss or downtime.
• Managed database services: You can quickly change to a more modern and cost-effective database engine with AWS DMS and get access to a host of fully-managed database services like Amazon Relational Database Service or Amazon Aurora. You also get the benefits of fully-managed data warehouse solutions like Amazon Redshift, NoSQL platforms such as Amazon DynamoDB or Amazon S3.
• Secured services: Database migration is a fully-secured process with AWS DMS. Data at rest in the source database is fully encrypted with the AWS Key Management Service (AWS KMS) while data in flight in transit to the target database is encrypted with the Secure Socket Layers (SSL).

All these benefits are very useful in the current data-driven business environment. 

Limitations of AWS DMS

Despite having multiple benefits, there are certain limitations of AWS DMS too. 

• Conversion Issues: There are a few conversion issues faced with AWS DMS during migration as data code and schema conversion is not handled directly by AWS DMS. Instead, for homogeneous migration, a schema has to be created at the target database and for homogeneous migration,the AWS SCT has to be used for the required conversions before migration.
• Additional coding required: For migrating incremental data after full load migration (Change Data Capture), some coding is required which can be a time-consuming activity.
• Ongoing replication problems: Anything not directly related to table data like indexes, users, and privileges cannot be processed by AWS DMS and only partial volumes of DDL (Data Definition Language) are replicated.
• System Slowdown: When source database resources are used to migrate large volumes of data with AWS DMS, there is often a slowing down of systems. Also, all queries for every task created during migration are placed on the source database, considerably impacting its efficiency.

These are some of the benefits and limitations of AWS DMS.