if you run a pod inside the vcluster and you run the same pod directly on the host cluster will be exactly the same in terms of computing power, storage access and networking. Implementation: This is mainly achieved by synchonizing pods which means that the pods are actually being scheduled and started just like regular pods of the underlying host cluster, i.e. The computing power, the access to underlying persistent storage as well as the network performance should not be degraded at all. Workloads running inside a vcluster (even inside nested vclusters) should run with the same performance as workloads which are running directly on the underlying host cluster. Implementation: This is mainly achieved by bundling the vcluster inside a single Pod using k3s as a control plane. Vclusters should be as lightweight as possible to minimize resource overhead inside the underlying host cluster. Vcluster has been designed following these principles: 1. Pods, ConfigMaps mounted in Pods) to the underlying host namespace, so that the scheduler of the underlying host cluster can schedule these pods. To be able to actually start containers, the vcluster synchronizes certain low-level resources (e.g. These objects only exist inside the virtual cluster and never reach the API server or data store (etcd) of the underlying host cluster. That applies in particular to all higher level Kubernetes resources, such as Deployments, StatefulSets, CRDs, etc. Generally, all Kubernetes resource objects that you create using the vcluster API server are stored in the data store of the vcluster (sqlite by default, see external datastore for more options). However, some low-level Kubernetes resources need to be synchronized to the underlying cluster. When working with the virtual cluster's API server, resources first only exist in the virtual cluster. API servers) that run on top of "real" Kubernetes clusters. The core idea of virtual clusters is to provision isolated Kubernetes control planes (e.g. It is possible to run multiple vclusters inside the same namespace and you can even run vclusters inside another vcluster (vcluster nesting). Everything that you create inside the vcluster lives either inside the vcluster itself or inside the host namespace. Each vcluster runs as a regular StatefulSet inside a namespace of the host cluster. Host Cluster & Namespace Įvery vcluster runs on top of another Kubernetes cluster, called host cluster. Then, the host cluster will schedule the pod and the vcluster will keep the vcluster pod and host cluster pod in sync. The vcluster uses a so-called syncer which copies the pods that are created within the vcluster to the underlying host cluster. (Optional) Scheduler (schedules workloads inside the virtual cluster.Controller Manager (creates pods objects in the data store according to replica number in ReplicaSets etc.).Data store (where the API stores all resources, real clusters run with etcd).Kubernetes API server (point your kubectl requests to this vcluster API server). Then, the host cluster will actually schedule the pod and the vcluster will keep the vcluster pod and host cluster pod in sync.Įach vcluster has its own control plane consisting of: Instead, it uses a so-called syncer which copies the pods that are created within the vcluster to the underlying host cluster. Syncer: What makes a vcluster virtual is the fact that it does not have actual worker nodes or network.You are also able to use another Kubernetes distribution as backing virtual cluster, such as k0s or vanilla k8s. You can also use a different data store, such as etcd, mysql or postgresql. By default, vclusters use sqlite as data store and run the API server and controller manager of k3s, which is a certified Kubernetes distribution and CNCF sandbox project. Control Plane: This container contains API server, controller manager and a connection (or mount) of the data store.vcluster - Architecture Components īy default, vclusters run as a single pod (scheduled by a StatefulSet) that consists of 2 containers: Instead, they are scheduling workloads inside the underlying cluster while having their own control plane. Compared to fully separate "real" clusters, virtual clusters do not have their own node pools or networking. Virtual clusters are Kubernetes clusters that run on top of other Kubernetes clusters.
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