Monthly Update October 2020

Posted October 16, 2020 by CloudUtil ‐ 6 min read


I’m happy to announce that the massive code change that has been in development since more than a year ago has been merged and after a few further improvements it’s now ready for Alpha/Beta testing by a wider audience.

What’s new?

Event-based instance replacement

In a nutshell, when deployed using the latest CloudFormation infrastructure code, AutoSpotting is now reacting to all new instance launches, in addition to the legacy cron-based execution mode that’s still available as before. Under normal circumstances newly launched on-demand instances are now immediately replaced with spot clones, avoiding to run the spot clone in parallel to the AutoScaling group they were launched for which has always been a quirk of AutoSpotting when compared to its alternatives.

In the relatively rare case that no spot instances could be launched or when running the latest AutoSpotting version without the infrastructure required for this event-based execution that we deploy from the current CloudFormation code (maybe if you’re running it as container on Kubernetes or the currently incomplete Terraform support) the on-demand instances would keep running and a spot instance is launched outside the group and will be replaced later by the legacy cron execution mode.

Other changes

To make this work, there were massive under-the-hood changes that will make it easier to add further improvements going forward that could handle various events from CloudTrail/CloudWatch Events. One such improvement already available in this latest version is the implementation of emulated instance startup lifecycle hooks for spot instances, by intercepting the API calls that fail for instances not yet added to the group, so we can emulate them in AutoSpotting. Similar handling would be possible in the future for other events, such as maybe the event emitted when detaching EBS volumes on instance termination could be handled by attaching the volume to a new spot instance towards supporting stateful workloads, or maybe other interesting use cases. Feel free to reach out or just create issues on Github if you have any such improvement ideas.

Main benefits

  • The spot clones are added immediately to the ASG, booting up as part of the ASG so they can set up immediately. Previously, in certain situations(Beanstalk, cfn-init) they could only be fully bootstrapped after they were swapped into the ASG, which was problematic. Also if the ASG was deleted by infrastructure code while a not yet replaced spot instance was still running outside the ASG, the stack couldn’t be deleted because of resources referenced by the still running spot instance(SGs, IAM roles, etc.). This should only happen when the spot instances failed to be launched immediately.

  • Handling of any number of concurrent instance launches, such in case of new ASGs or when scaling out with multiple instances at once. In such cases the ASG is a bit “confused” by all the attach/detach action and briefly shows some strange numbers for the desired capacity, but when using CloudFormation we have code that helps it eventually converge to the previous capacity by temporarily suspending some of the AutoScaling processes that react in weird ways to this capacity churn. This code is not yet available when using the Terraform deployment method and may still be buggy but it seemed to work pretty well in our initial tests.

  • Besides the obvious cost implications of only paying on-demand for the first minute, this change also makes AutoSpotting a decent option for relatively short-lived AutoScaling groups where the legacy instance replacement mode previously made it unusable.

  • Emulated handling of startup lifecycle hooks for spot instances and significant under the hood improvements that will allow implementation of other interesting use cases, such as support for stateful workloads, etc.

Known issues

  • This code is relatively new and bugs are definitely still lurking around, so I’m looking for some brave people to try it out, report issues to help mature it further. As always, anyone submitting issues on Github or contributing to the code base receive access to my commercially available stable builds for a year after their contribution, currently charged at $29/month/AWS account.
  • The Terraform/Kubernetes deployment methods weren’t yet tested and don’t implement the full support infrastructure currently available from the CloudFormation template, especially the part needed for handling the multiple simultaneous instance replacements by suspending the AutoScaling processes. This may have other consequences impacting the instance replacements, so I’d like to see some contributions from the community to help bring it up-to-speed with what we have in CloudFormation or at least ensure it works in legacy mode. Unfortunately I don’t have enough bandwidth to support all deployment methods and need to focus my effort on CloudFormation.

Next steps

For the near future I’m planning to focus on maturing this recent code towards making it production-grade but once this is achieved, I’ll try to look into the following pieces of functionality:

  • Handling of ICE situations on the ASG’s main on-demand instance type - #439
  • Support for stateful workloads - #440
  • Use Dynamic instance type information instead of the current instance type database shipped within the Lambda payload - #441
  • Support for China and GovCloud regions - #442 and #443

As I mentioned before, some of these advanced features may only be made available commercially to my Patreon supporters, as a sort of Premium package, but I’d like to get your feedback on this.

Ways for you to help

  • Install the latest nightly version from here, and provide feedback about it. Keep in mind that this may be buggy, so please handle it with care.
  • If you can’t code and still want to contribute to the development effort, I’d love to get your support on Patreon through signing up for the stable builds or the other available support options, or on Github Sponsors for no-strings-attached sponsorship. Any income I receive from these is helping me allocate more time to the development of AutoSpotting on a weekly basis.
  • I’m always thinking about ways to improve AutoSpotting, the above roadmap is enough to keep me busy for a long time and you can always influence it by creating or voting on existing Github issues . As always, Github issues created by Patreon supporters have higher priority, so if you are supporting the project and would like to see anything in particular, I’d love to hear from you.


  • Thanks to everyone who contributed code or feedback towards this release, especially mello7tre, Gabe Gorelick and Christopher Farrenden , who helped me a lot over the last few months of getting this over the line.
  • Also thanks to my former employer Here Technologies who sponsored the initial development of this work.
  • This version wouldn’t be available if it wasn’t for my supporters on Patreon and Github Sponsors, who kept me motivated to keep working on it over the last year. Huge thanks to you all!
  • Thank you for reading so far, this ended up much longer that I expected ;-)

As always, feel free to reach out to me by answering this email or on Gitter if you have any feedback, questions or concerns.

Best regards,