Public cloud infrastructure provider Amazon Web Services (AWS) today talked about Blox software that it has open-sourced to let developers create custom schedulers for use inside AWS’ EC2 Container Service (ECS).

The first two components of the Blox software, a “reference scheduler” and a service for capturing data on clusters that can then be queried, are available now on GitHub under an Apache 2.0 license.

Developers “really want to have more control over their own schedulers,” and they “want to be able to test locally,” Amazon vice president and chief technology officer Werner Vogels said at AWS’ re:Invent user conference in Las Vegas.

Containers are a lightweight alternative to more traditional virtual machines (VMs) that have risen to popularity in the past few years, particularly after startup Docker open-sourced its container technology in 2013. One quality of containers that helped them gain adoption is their ability to be moved from machine to machine with very little work. That’s relevant in situations where software development is happening quickly and companies don’t want to get stuck forever in one cloud or data center.

All the biggest public clouds — AWS, Microsoft Azure, and Google Cloud Platform — have since come out with services for running containers and storing container images on their infrastructure.

Now AWS is effectively making its deployment service easier to tinker with, rather than requiring the use of third-party schedulers such as Google-backed Kubernetes, Mesosphere’s Mesos, or Docker’s own Swarm.

AWS principal product manager Chris Barclay has published a detailed blog post on using the Blox tools.