Rolling Update with AWS CloudFormation

Michael Wittig – 18 Jan 2016

Updating all EC2 instances in an Auto Scaling Group becomes complex and expensive when done manually. If you follow the immutable infrastructure approach you will roll out a new version by creating new EC2 instances. You never change the old instances. But how do you deploy security patches of the OS or a new version of your application automatically? One option is using AWS CloudFormation.

CloudFormation supports the UpdatePolicy attribute for Auto Scaling Groups. You can define that CloudFormation performs a rolling update of instances whenever the Launch Configuration changes. A rolling update will roll out your change in small batches.

Here is an example. Let’s say we have 4 EC2 instances running version A (grey) and a batch size of 2. Now we roll out version B (dark). Have a look at the following animation.

Rolling update animation

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  1. Two EC2 instances with version B are started (blue).
  2. Wait until both new EC2 instances running version B are in service (dark). You now have 6 EC2 instances running.
  3. Terminate the two oldest EC2 instances running version A. You now have 4 EC2 instances running.
  4. Two EC2 instances with version B are started (blue).
  5. Wait until both new EC2 instances running version B are in service (dark). You now have 6 EC2 instances running.
  6. Terminate the two oldest EC2 instances running version A. You now have 4 EC2 instances running.
  7. Done.

The following CloudFormation template is enriched with some vocal comments and line highlighting. Press the play button and enjoy the show.

How do you like CloudFormation templates annotated with voice? Let me know!

Try rolling updates with our CloudFormation template:

  1. Launch Stack
  2. Click Next to proceed with the next step of the wizard.
  3. Specify a name and all parameters for the stack. Set VersionParameter to 1.
  4. Click Next to proceed with the next step of the wizard.
  5. Click Next to skip the Options step of the wizard.
  6. Click Create to start the creation of the stack.
  7. Wait until the stack reaches the state CREATE_COMPLETE.
  8. Open the Outputs tab and click on the provided ELB URL. You should see a white page that contains Version 1 text.
  9. In the CloudFormation console, select the stack, click the Actions button at the top, select Update Stack.
  10. Click Next to proceed with the next step of the wizard.
  11. Change the VersionParameter to 2.
  12. Click Next to proceed with the next step of the wizard.
  13. Click Next to skip the Options step of the wizard.
  14. Click Update to update the stack.
  15. Go back to the page (ELB URL) and reload every now and then. After a few minutes it should switch to Version 2.
  16. Don’t forget to delete the CloudFormation stack!
Michael Wittig

Michael Wittig

I’m an independent consultant, technical writer, and programming founder. All these activities have to do with AWS. I’m writing this blog and all other projects together with my brother Andreas.

In 2009, we joined the same company as software developers. Three years later, we were looking for a way to deploy our software—an online banking platform—in an agile way. We got excited about the possibilities in the cloud and the DevOps movement. It’s no wonder we ended up migrating the whole infrastructure of Tullius Walden Bank to AWS. This was a first in the finance industry, at least in Germany! Since 2015, we have accelerated the cloud journeys of startups, mid-sized companies, and enterprises. We have penned books like Amazon Web Services in Action and Rapid Docker on AWS, we regularly update our blog, and we are contributing to the Open Source community. Besides running a 2-headed consultancy, we are entrepreneurs building Software-as-a-Service products.

We are available for projects.

You can contact me via Email, Twitter, and LinkedIn.

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