Mixing means composing an OS for a specific use case. The default build of the Clear Linux* OS provides options to install bundles for various server capabilities. However, you could wish to supplement the operating system with functionality from other distributions.
You can use the mixer tool to add custom packages to the Clear Linux OS. For example, developer does not want to build, install, and run a whole custom OS image to overlay some small piece of software. With the mixer tool, you can add that piece and yet remain within the OS’s update stream. The mixer tool works similarly to what a system administrator is accustomed when adding functionality on top of RHEL*, CentOS*, SLES*, or Ubuntu*. Similarly, you can start mixing with a source tar file or RPM. The end result includes the added pieces mixed on top of the existing official mix.
The mixer tool can also help you modify core components of the OS. If you are already accustomed to building your own OS, you can take an existing reference implementation, such as CentOS, add a few patches, packages and settings before building using the mixer. The mixer in this scenario gives you an alternative update stream to build, maintain, and serve your machines beyond the update stream provided by the Clear Linux OS.