Reduce your AWS spend by deleting idle DMS instances

Movement is life.

– Brad Pitt as Gerry Lane in World War Z

Table of contents#

1. Why idle DMS instances are costing you thousands of dollars
2. How to find and delete idle DMS instances
3. Eliminate idle DMS instances easily and automatically with CloudFix

As a film buff, I love a good movie reference. In our Cost and Usage report foundation blog, I used the classic Star Trek II: Wrath of Khan to introduce the importance of detailed knowledge of the CUR. Today, let’s fast forward to a relatively new cult classic from 2013, World War Z. World War Z is a modern take on a classic zombie invasion movie, starring Brad Pitt as the hero and main character. Early in the movie, there’s a scene where Pitt and several other characters are deciding whether to hunker down or run to seek a more stable and safer place. Pitt’s character said a phrase that has always stuck with me: movement is life. 

Although not as dramatic as a horde of zombies, moving your data from one database to another can also be scary. Without careful planning and reliable execution, your application data can become a collection of useless bits. But, movement is life. If you’re facing a situation where you want to decommission your on-prem database and move it into the cloud, you will eventually have to face the daunting task of moving the database to the safety and security of AWS. And although we will not have Brad Pitt’s help, we do have a useful tool at our disposal, the Amazon Database Migration Service. 

The Amazon Database Migration Service (DMS) is a paid service from AWS that facilitates the migration of an active database to, from, or within AWS. Its key features include high availability, minimal downtime, ongoing data replication, and support for a wide variety of source and target databases. The migration work itself is done by a special-purpose EC2 instance called a replication instance. These do the heavy lifting of moving the data from A to B and, just like standard EC2 instances, they incur costs whether they are busy or idling. 

The only problem: like zombies, idle DMS instances tend to add up, and there’s no reason to pay for something we’re not using. Let’s look at how much these idle resources cost and how we can successfully destroy – err, delete – them.

1. Why idle DMS instances are costing you thousands of dollars#

Idle DMS instances add up for the same reason that other idle resources do: we use them and forget about them and/or we get overly nervous about the risks of deleting them. Fortunately, it’s relatively simple to identify which DMS instances are truly idle and can therefore be safely eliminated – and it’s definitely beneficial from a cost perspective.

When you use AWS DMS in the standard (non-serverless) method, the cost driver is the DMS replication instance. The DMS pricing page states, “AWS Database Migration Service currently supports the T2, T3, C4, C5, C6i, R4, R5, and R6i instance classes.” DMS replication instances are priced in proportion to their underlying instance type and size, and single vs. multi-AZ configurations.

Comparing EC2 On-Demand and DMS On-Demand pricing, using us-east-1 in Sept 2023 as a reference, we see the following pricing:

In simple terms, DMS Single-AZ costs double the underlying instance type, and DMS Multi-AZ costs double that. Given that DMS instances can be left running for weeks or even months, these costs can quickly become significant. A c6i.16xlarge DMS Single-AZ instance left sitting idle for just 30 days will accumulate roughly $3,560 in charges! That’s a lot of potential for wasted spend.

To give some more concrete numbers, one organization that we worked with was spending ~$40K per month on DMS, with the vast majority of the cost attributable to DMS migration instances. Of this cost, 90% of the DMS instances were idle (long unused). A 90% cost reduction is always something to celebrate!

In this case, $40K of annual spend was reduced to $4K, and that is with a very cautious approach. We expect most users of DMS to see similar savings, especially in large organizations where things like idle infrastructure can easily slip through the cracks.

2. How to find and delete idle DMS instances#

Finding idle replication instances by hand means listing every DMS instance across every account and region, then checking each one for signs of recent or ongoing migration work before you dare delete it. Database migrations are often mission-critical, so the definition of “idle” needs to be cautious.

CloudFix does this read-only, using your cost and usage data and the DMS service’s own information about each replication instance and its tasks to find instances that have gone unused for an extended period. Each idle instance appears in your Recommendations for you to approve. Once you approve, the fixer runs as an AWS Systems Manager Automation runbook in your own account, removes the instance’s replication tasks and then deletes the replication instance, and every execution is logged.

3. Eliminate idle DMS instances easily and automatically with CloudFix#

Doing this by hand isn’t too tedious, but it’s also not something that’s a top priority to your team. That means it tends to go undone, and THAT means that those expensive instances keep adding up. 

With CloudFix, you can just set it and forget it. Our finder/fixer uses a cautious definition of idle and deletes idle DMS instances automatically. All you need to do is approve the proposed changes and CloudFix will do the rest. That’s thousands of dollars of reclaimed budget – and thousands of fewer zombie DMS instances roaming the streets of AWS. 

Curious how much you can save by deleting idle DMS instances with CloudFix? Check out our free savings assessment. Quickly and securely, you’ll discover which CloudFix fixers, like this one, can be applied to your environment and exactly how much you can save.

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