vCluster glossary
This page contains definitions for common terms used throughout the vCluster documentation.
Admission Control
A Kubernetes feature that intercepts requests to the API server prior to persistence of the object, allowing for validation, mutation, or rejection of requests based on configured policies.
Related terms: API Server, Control Plane
API Server
The core component of Kubernetes that exposes the Kubernetes API. It is the front-end for the Kubernetes control plane and handles all REST operations, validating and configuring data for API objects.
Related terms: Control Plane, rate-limiting
Compaction
The process of removing superseded data from etcd to free up storage space. Regular compaction prevents etcd from running out of disk space.
Related terms: etcd, Defragmentation
Control Plane
The container orchestration layer that exposes the API and interfaces to define, deploy, and manage the lifecycle of containers. In vCluster, each virtual cluster has its own control plane components.
Related terms: API Server, vCluster
Control Plane Cluster
The Kubernetes cluster that hosts the virtualized control planes for tenant clusters. The Control Plane Cluster is operated by the platform provider and is completely invisible to tenants. There are no shared control plane nodes, no in-cluster agent pods, and no lateral path between tenant environments. With shared nodes, this cluster also runs tenant workloads alongside the control plane pods — the same node pool is used for both.
Related terms: Virtual Cluster, Host Cluster, Tenant Cluster
Defragmentation
The process of releasing unused space in etcd's backend database after compaction. While compaction marks space as free, defragmentation reclaims it.
Related terms: etcd, Compaction
etcd
A distributed key-value store that provides reliable storage for Kubernetes cluster data. In vCluster, etcd can be deployed externally or embedded within the vCluster pod.
Related terms: Control Plane
Host Cluster
The physical Kubernetes cluster where virtual clusters are deployed and run. The host cluster provides the infrastructure resources (CPU, memory, storage, networking) that virtual clusters leverage, while maintaining isolation between different virtual environments.
Related terms: Virtual Cluster, Control Plane Cluster
K0s
A lightweight, certified Kubernetes distribution that can be used in virtual clusters as an alternative to K3s or standard Kubernetes.
Related terms: K3s, K8s
K3s
A lightweight, certified Kubernetes distribution often used as the default distribution for virtual clusters due to its minimal resource requirements and fast startup time.
Related terms: K8s, K0s
K8s
The standard Kubernetes distribution that can be used in virtual clusters, offering full compatibility with upstream Kubernetes features.
Related terms: K3s, K0s
Multi-tenancy
The capability to host multiple separate users, teams, or workloads on the same infrastructure while providing isolation between them. Virtual clusters enhance multi-tenancy in Kubernetes environments.
Related terms: Virtual Cluster
Pseudo Nodes
The default node representation in a tenant cluster. vCluster creates pseudo nodes for each host node that has pods scheduled on it. Pseudo nodes have real values for name, CPU, architecture, and operating system, but all other fields are randomly generated. When no pods remain on a host node, vCluster deletes the corresponding pseudo node.
Related terms: Syncer, Control Plane Cluster
Syncer
A component in vCluster that synchronizes resources between the virtual cluster and the host cluster, enabling virtual clusters to function while maintaining isolation.
Related terms: vCluster, Virtual Cluster
Tenant Cluster
A fully isolated Kubernetes environment provisioned for a single tenant. Each tenant cluster has its own API server, controller manager, and resource namespace, backed by a virtualized control plane hosted on a Control Plane Cluster. From the tenant's perspective it behaves exactly like a standard Kubernetes cluster.
Related terms: Control Plane Cluster, Virtual Cluster
vCluster
An open-source software product that creates and manages virtual Kubernetes clusters inside a host Kubernetes cluster. vCluster improves isolation and multi-tenancy capabilities while reducing infrastructure costs.
Related terms: Virtual Cluster, Host Cluster
Virtual Cluster
A certified Kubernetes distribution that runs as an isolated, virtual environment nested inside a physical host cluster. Virtual clusters run inside host cluster namespaces but operate as independent Kubernetes environments, each with its own API server, control plane, syncer, and set of resources.
Related terms: vCluster, Host Cluster