What is OperatingSystemManager?
Operating System Manager (OSM) is an open source project by Kubermatic, it is responsible for creating and managing the required configurations for worker nodes in a Kubernetes cluster. It decouples operating system configurations into dedicated and isolable resources for better modularity and maintainability.
These isolated and extensible resources allow a high degree of customization which allows users to modify the worker node configurations to suit their use cases. This is useful for hybrid, edge, and air-gapped environments.
Configurations for worker nodes comprise of set of scripts used to prepare the node, install packages, configure networking, storage etc. These configurations prepare the nodes for running
Machine-Controller is used to manage the worker nodes in KubeOne clusters. It depends on user-data plugins to generate the required configurations for worker nodes. Each operating system requires its own user-data plugin. These configs are then injected into the worker nodes using provisioning utilities such as cloud-init or ignition. Eventually the nodes are bootstrapped to become a part of a kubernetes cluster.
This has been the norm till machine-controller v1.54.0 and it works as expected. Although over time, it has been observed that this workflow has certain limitations.
Machine Controller Limitations
- Machine Controller expects ALL the supported user-data plugins to exist and be ready. User might only be interested in a subset of the available operating systems. For example, user might only want to work with
- The user-data plugins have templates defined in-code. Which is not ideal since code changes are required to update those templates. Then those code changes need to become a part of the subsequent releases for machine-controller and KubeOne. So we need a complete release cycle to ship those changes to customers.
- Managing configs for multiple cloud providers, OS flavors and OS versions, adds a lot of complexity and redundancy in machine-controller.
- Since the templates are defined in-code, there is no way for an end user to customize them to suit their use-cases.
- Each cloud provider sets some sort of limits for the size of
user-data, machine won’t be created in case of non-compliance. For example, at the time of writing this, AWS has set a hard limit of 16KB.
- Better support for air-gapped environments is required.
Operating System Manager was created to overcome these limitations.