What Is a Kubelet?

A kubelet is a critical component within Kubernetes architecture. It is the primary node agent — the administrative agent that monitors application servers and routes administrative requests to servers — that runs on each node in a Kubernetes cluster. It plays a pivotal role in ensuring that the containers are running and properly managed within the node. Essentially, it’s the key liaison between the Kubernetes active controller and the nodes within the cluster.

This node agent is responsible for overseeing the execution of containers on the node by interacting with the container runtime, which could be Docker, containerd, or another compliant runtime. The kubelet receives Podspecs, which are specifications for a set of one or more containers, from the Kubernetes active controller, then ensures that the containers described in those Podspecs are launched and operating as expected.

The kubelet performs other essential tasks, including monitoring the health of containers, ensuring that they’re in the desired state according to the Podspecs, managing container lifecycles (starting, stopping, and restarting), and reporting back to the control plane about the node’s status. It also manages resources such as CPU, memory, and storage on the node by handling Pod resource consumption and limits, ensuring that the containers do not exhaust the node’s resources.

In short, the kubelet is a crucial component that acts as the node-level supervisor within a Kubernetes cluster, responsible for the proper execution and management of containers. It ensures that the node maintains the desired state as defined by the Kubernetes active controller.

A node agent, in the realm of computer systems and network management, refers to a software component or entity responsible for handling specific tasks and maintaining operations within a computing node or a network node. Its primary function is to monitor, manage, and control activities and resources on the node it operates on.

In the context of distributed systems such as Kubernetes, a node agent — such as the kubelet — plays a critical role in managing the individual nodes within a cluster. Specifically, the kubelet acts as a node-level agent responsible for overseeing the execution of containers within each node. It communicates with the control plane, adhering to instructions and specifications for deploying and managing containers, ensuring that they run as defined by the received Podspecs.

The node agent is the primary interface between the higher-level orchestration system (such as Kubernetes active controller components) and the individual node’s resources. It monitors the state of the node, manages container lifecycles, handles resource allocation, and reports back to the centralized management system about the status and health of the node and its containers. The node agent is pivotal in maintaining the desired state of the node, ensuring that containers are running, and handling any necessary actions to maintain the node’s functionality within the larger cluster. Its responsibilities include resource management, container execution, and maintaining communication with the orchestration platform to ensure the synchronization of the node’s state with the desired configuration.

A node agent acts as a local manager and executor, taking care of node-specific operations to maintain the health and functionality of the node within a larger distributed computing system, playing a crucial role in ensuring the proper execution and management of workloads on individual nodes within a cluster. The kubelet is a type of node agent.

Kubernetes architecture is a robust, scalable, and portable open source platform designed for automating deployment, scaling, and management of containerized applications. It streamlines the process of managing and orchestrating containers, offering a highly resilient and flexible infrastructure for modern, cloud-native applications.

Kubernetes operates on a cluster-based model, with a collection of nodes working together to form a cohesive environment. The key components of Kubernetes architecture are:

• Control plane: This element of the network architecture is responsible for managing and controlling the overall behavior of the network, handling routing decisions, network policies, configuration changes, and more. The control plane focuses on the high-level management and coordination of network devices.
• Active controller node: A specific hardware or software entity within the network, the controller node manages and coordinates the overall operating of the system. It oversees tasks such as resource allocation, communication between nodes, and overall system orchestration.
• Worker node: These nodes, also known as minions, form the foundation of the cluster where the actual workloads run. Each worker node hosts multiple containers via a container runtime (such as Docker or containerd) and contains various components, the primary one being the kubelet. The kubelet is responsible for managing the pods and their containers, ensuring that they are running as specified in the pod configuration received from the control plane. Additionally, there’s the kube-proxy, which acts as the network proxy on the node to enable communication across the cluster.
• Pods: The fundamental scheduling unit in Kubernetes, pods consist of one or more containers that share networking and storage resources. They represent the smallest deployable units that can be managed by Kubernetes.

Kubernetes architecture allows high availability, scalability, and ease of management. It automates the distribution and management of applications, effectively handling scaling, load balancing, self-healing, and rolling updates. This infrastructure model enables the seamless deployment and management of containerized applications across various environments, whether on-premises, in the cloud, or in hybrid setups.

In a real-time operating system (RTOS) environment, the kubelet is particularly vital but can also be more challenging, due to the unique requirements of these systems. An RTOS, such as VxWorks^® from Wind River^®, is designed for applications in which deterministic timing and rapid response times are critical. The kubelet in an RTOS environment plays a pivotal role in handling the orchestration of containers while considering the real-time constraints.

The significance lies in several important areas:

• Resource allocation and real-time constraints: A kubelet in an RTOS needs to manage resources and schedule containers within strict timing requirements. It must ensure that containerized applications operate within the specified time constraints without affecting the determinism and behavioral predictability of the system.

• Reliability and safety-critical operations: In industries such as aerospace, automotive, and industrial automation, where VxWorks is often employed, safety-critical applications are the norm. The kubelet’s role becomes even more crucial, since it must manage the deployment and operation of containerized applications without compromising the system’s safety and reliability.
• Integration and adaptation: Integrating Kubernetes components, including the kubelet, into an RTOS environment such as VxWorks requires adaptations to meet the environment’s constraints and specific requirements. This integration involves ensuring that Kubernetes functionality aligns with the real-time characteristics of the operating system.
• Management and monitoring: The kubelet in an RTOS setting is responsible for monitoring the health of containers, handling the lifecycle of these containers, managing their real-time capabilities, and ensuring that they operate within the defined constraints — again, without jeopardizing the system’s predictability and determinism.
• Extended capabilities: Deploying Kubernetes in RTOS environments extends the reach of container orchestration and management to critical industries, opening up possibilities for modernizing and standardizing the management of real-time systems.

The kubelet’s role is crucial in bringing modern orchestration capabilities to specialized, high-stakes industries while ensuring the integrity and stability of the systems they rely on.

Wind River developed and contributed the open source code that brought containers to Wind River Linux. We implemented container support for VxWorks, first with VxPOD in 2016 and more recently with OCI-compliant containers. Our vision for containers in embedded systems is enhanced by our experience of supporting the Kubernetes container-based StarlingX project for telecommunications.

VxWorks Kubelet

VxWorks is the industry’s most trusted and widely deployed real-time operating system (RTOS) for mission-critical embedded systems and is the first RTOS to support OCI-compliant containers. It delivers a proven, real-time, and deterministic runtime combined with a modern approach to development. Across industries, companies building intelligent edge systems rely on the VxWorks pedigree of security, safety, high performance, and reliability.

The VxWorks Kubernetes kubelet refers to the kubelet component specifically designed for VxWorks-based systems to integrate with Kubernetes clusters.

The VxWorks kubelet, much like a traditional kubelet in the Kubernetes architecture, is the node agent that manages containers on VxWorks-based nodes within a Kubernetes cluster. It interfaces with the Kubernetes control plane to receive instructions, primarily Podspecs that describe the containers’ configurations and ensure the deployment and execution of these containers within the VxWorks environment.

This specialized kubelet for VxWorks enables the deployment and orchestration of containerized applications in scenarios in which VxWorks is the underlying operating system, allowing the incorporation of Kubernetes-based management and automation into industries that rely on VxWorks for their critical systems. It caters to the specific requirements and intricacies of embedded and real-time systems by extending Kubernetes capabilities to these environments.

VxWorks kubelet integration with Kubernetes aligns with the broader trend of extending Kubernetes’ reach to diverse platforms, including those in Industrial IoT and embedded systems, fostering standardization and consistent management practices across a wide array of computing environments.

Wind River Studio Cloud Platform

Wind River Studio Cloud Platform is an open source, production-grade distributed Kubernetes solution for managing edge cloud infrastructure. Based on the OpenStack StarlingX project, the cloud platform in Studio represents a compilation of best-in-class open source technology that delivers the features needed to effectively deploy and manage distributed networks.

With a series of groundbreaking firsts, Studio has become an essential partner to Tier 1 operators worldwide, including Verizon and Vodafone. Customers select Cloud Platform to control costs, support new revenue streams, take advantage of deployment-ready open source, and establish market leadership.