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Mark Bishop
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## What's a Kubernetes Cluster?
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A cluster is a group of computing resources that work as a team to accomplish a goal. Each individual computer in a cluster is called a _node_.
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In the IT world, a cluster is a group of computing resources that work as a team to accomplish a goal.
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## Cluster Creation
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A _Kubernetes Cluster_ is a cluster that uses the [Kubernetes container-orchestration system](https://kubernetes.io/) to deploy, maintain, and scale Docker containers, allowing your organization to automate application operations. Kubernetes reduces the manual processes of maintaining organization operations.
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Rancher simplifies creation of Kubernetes clusters by allowing you to create them with the Rancher UI rather than a config file.
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### Kubernetes Cluster Node Components
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### Node Components
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A Kubernetes cluster contains 3 types of nodes: etcd nodes, control plane nodes, and worker nodes.
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Each computing resource in a Kubernetes Cluster is called a _node_. Node can be either bare-metal servers or virtual machines. Kubernetes (here after, K8s) classifies nodes into three distinct types: _etcd_ nodes, _control plane_ nodes, and _worker_ nodes. Understanding the role of each node will help you create your own K8s cluster.
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#### etcd Nodes
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The etcd nodes are used to run the etcd database. etcd is a key value store used as Kubernetes’ backing store for all cluster data. Even though you can run etcd on a single node, you need 3, 5, or 7 nodes for redundancy.
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[etcd](https://kubernetes.io/docs/concepts/overview/components/#etcd) nodes run the `etcd` database. The `etcd` database component is a key value store used as K8s storage for all cluster data, such as cluster coordination and state management.
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`etcd` is a distributed key value store, meaning it runs on multiple nodes so that there's always a backup available for fail over. Even though you can run `etcd` on a single node, you should run it on multiple nodes. We recommend 3, 5, or 7 nodes for redundancy.
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#### Control Plane Nodes
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The control plane nodes are used to run the Kubernetes API server, scheduler, and controller manager. Control plane nodes are stateless since all cluster data are stored on etcd nodes. You can run control plane on 1 node, although 2 or more nodes are required for redundancy. You can also run control plane on etcd nodes.
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[Control plane](https://kubernetes.io/docs/concepts/#kubernetes-control-plane) nodes run the K8s API server, scheduler, and controller manager. These nodes take care of routine tasks to ensure that your K8s cluster is running according to your configuration. Because all cluster data is stored on your `etcd` nodes, control plane nodes are stateless. You can run control plane on a single node, although two or more nodes are recommended for redundancy. Additionally, you can a single node can share the control plane and `etcd` roles.
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#### Worker Nodes
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Worker nodes are used to run the kubelet and the workload. It also runs the storage and networking drivers and ingress controllers when required. You create as many worker nodes as needed for your workload needs.
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[Worker nodes](https://kubernetes.io/docs/concepts/architecture/nodes/) run:
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-_kubelets_, which is an agent that monitors the state of the node, ensuring your containers are healthy.
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- _workloads_, which are the containers and pods that hold your apps, as well as other types of deployments.
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Using Rancher, you can create Kubernetes clusters using a variety of options. Use the option that best fits your use case.
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Worker nodes also run storage and networking drivers, and ingress controllers when required. You create as many worker nodes as needed for your workload needs.
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## Hosted Kubernetes Providers
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## Cluster Creation in Rancher
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By integrating with cloud APIs, Rancher lets you create new Kubernetes clusters through hosted providers, all within the Rancher UI. You can create clusters using either:
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Now that you know what a K8s Cluster is, how does Rancher fit in?
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- A hosted Kubernetes provider, such as Google GKE, Amazon EKS, or Microsoft AKS.
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- An IaaS provider, using nodes provided from Amazon EC2, Microsoft Azure, or DigitalOcean.
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Rancher simplifies creation of K8s clusters by allowing you to create them through the Rancher UI rather than more complex alternatives. Rancher provides multiple options for launching a K8s cluster. Use the option that best fits you use case.
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## Rancher-Launched Kubernetes
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## Cluster Creation Options
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Alternatively, you can use Rancher to create a cluster from your own existing nodes, using RKE. RKE is Rancher’s own lightweight Kubernetes installer. It works with any bare metal server, cloud provider, or virtualization platform. It integrates with node drivers to automatically provision nodes on AWS, Azure, DigitalOcean, vSphere, OpenStack, etc. Users can add custom nodes to the cluster by running the Rancher agent on these nodes.
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Options include:
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## Kubernetes Importation
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<!-- TOC -->
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Finally, you also have the option of importing an existing Kubernetes cluster that you're already using into Rancher.
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- [Hosted Kubernetes Cluster](#hosted-kubernetes-cluster)
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- [RKE Clusters](#rke-clusters)
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- [Node Pools (i.e., Infrastructure Provider)](#node-pools-ie-infrastructure-provider)
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- [Custom Nodes (i.e. Existing Nodes)](#custom-nodes-ie-existing-nodes)
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- [Import Existing Cluster](#import-existing-cluster)
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Using Rancher, you can create Kubernetes clusters using a variety of options. Use the option that best fits your use case.
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<!-- /TOC -->
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## Hosted Kubernetes Providers
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### Hosted Kubernetes Cluster
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If you already have a cluster hosted by a Kubernetes provider such as Google GKE, Rancher can integrate with its cloud APIs, allowing you to manage your hosted cluster from the Rancher UI.
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If you already use a K8s provider such as Google GKE, Rancher can integrate with its cloud APIs, allowing you to create and manage your hosted cluster from the Rancher UI.
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## Infrastructure Providers
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[Hosted Kubernetes Cluster]({{< baseurl >}}/rancher/v2.x/en/clusters/hosted-kubernetes-clusters)
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Using Rancher, you can leverage APIs from major IaaS providers to create nodes and provision a new Kubernetes cluster.
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### RKE Clusters
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## From Existing Nodes
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Alternatively, you can use Rancher to create a cluster from your own existing nodes, using RKE. RKE is Rancher’s own lightweight K8s installer. It works with any bare metal server, cloud provider, or virtualization platform. It integrates with node drivers to automatically provision nodes on AWS, Azure, DigitalOcean, vSphere, OpenStack, etc. Users can add custom nodes to the cluster by running the Rancher agent on these nodes.
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Use Rancher to create a Kubernetes cluster on your on-premise bare metal servers. This option creates a cluster using RKE, which is Rancher's own lightweight Kubernetes installer.
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[RKE Clusters]({{< baseurl >}}/rancher/v2.x/en/clusters/rke-clusters)
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#### Node Pools (i.e., Infrastructure Provider)
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Using Rancher, you can leverage APIs from major IaaS providers in combination with RKE to create nodes and provision a new K8s cluster.
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[Node Pools]({{< baseurl >}}/rancher/v2.x/en/clusters/rke-clusters/#node-pools)
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#### Custom Nodes (i.e. Existing Nodes)
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Use Rancher to create a K8s cluster on your on-premise bare metal servers. This option creates a cluster using RKE, which is Rancher's own lightweight K8s installer.
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In addition to bare metal servers, RKE can also create clusters on less popular IaaS providers by integrating with node drivers.
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## Import Existing Clusters
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[Custom Nodes]({{< baseurl >}}/rancher/v2.x/en/clusters/rke-clusters/#custom-nodes)
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Users can import an existing Kubernetes cluster into Rancher. Rancher does not automate the provisioning, scaling, and upgrade of imported Kubernetes clusters. All other cluster management, policy management, and workload management capabilities of Rancher apply to imported clusters.
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### Import Existing Cluster
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Users can import an existing K8s cluster into Rancher. Rancher does not automate the provisioning, scaling, and upgrade of imported K8s clusters. All other cluster management, policy management, and workload management capabilities of Rancher apply to imported clusters.
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[Importing Existing Cluster]({{< baseurl >}}/rancher/v2.x/en/clusters/imported-clusters/)
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