# Cloud Provider

When running within a cloud platform, Kubernetes is supercharged by a Cloud Provider, harnessing in-built features of the platform such as persistent volume, load balancing, networking, DNS resolution, and auto-scaling.

## Meet the Regulars

Kubernetes comes pre-installed with a trove of Cloud Providers. Frequent flyers include:

* GCE
* AWS
* Azure
* Mesos
* OpenStack
* CloudStack
* Ovirt
* Photon
* Rackspace
* Vsphere

## A Peek Under the hood – How do Cloud Providers Work?

* For apiserver, kubelet, and controller-manager, cloud provider options are set.
* The Kubelet:
  * Connects with the Cloud Provider interface to retrieve the node name.
  * Informs the API Server about the InstanceID, ProviderID, ExternalID and Zone during Node registration.
  * Frequently checks if new IP addresses have been added to the Node.
  * Sets unschedulable conditions until cloud service provider completes routing configuration.
* The kube-apiserver:
  * Distributes SSH keys to all nodes for SSH tunnel creation.
  * The PersistentVolumeLabel takes care of PV labels.
  * The PersistentVolumeClainResize dynamically expands PV size.
* The kube-controller-manager:
  * Node controller checks the status of the VM where the Node resides. If the VM is deleted, it automatically removes the corresponding Node from the API Server.
  * Volume controller interacts directly with the cloud provider to create or delete persistent storage volumes, and mounts or unmounts them onto the specified VM as needed.
  * Route controller configures cloud routes for all registered Nodes.
  * Service controller creates load balancer for services of LoadBalancer type and updates the service's external IP.

## Standalone Cloud Provider: How Does It Work and Track Progress?

Follow the [principle](https://kubernetes.io/docs/tasks/administer-cluster/running-cloud-controller/) and [progress tracking](https://github.com/kubernetes/features/issues/88) guidelines to understand:

* Kubelet must be configured with `--cloud-provider=external`, and neither `kube-apiserver` nor `kube-controller-manager` should have the cloud provider configured.
* The `kube-apiserver` admission control options must not include PersistentVolumeLabel.
* The `cloud-controller-manager` works independently and activates `InitializerConifguration`.
* Kubelet can configure `ExternalID` through the `provider-id` option. After starting, it will automatically add a taint to Node as `node.cloudprovider.kubernetes.io/uninitialized=NoSchedule`.
* `Cloud-controller-manager` will reinitialize Node configuration after receiving Node registration event, add information such as zone or type, and remove the taint automatically created by Kubelet in the previous step.
* Merging the cloud-related logic of kube-apiserver and kube-controller-manager is the primary task.
  * View steps for the Node, Volume, Route and Service controllers above.
  * The PersistentVolumeLabel admission controller takes care of PV labels.
  * The PersistentVolumeClainResize admission controller dynamically expands PV size.

## Developing Your Own Cloud Provider Extension

The current Kubernetes Cloud Provider is under restructuring:

* v1.6 added the standalone `cloud-controller-manager` service, enabling cloud providers to build their own `cloud-controller-manager` without having to touch Kubernetes' core code.
* v1.7-v1.10 further separated `cloud-controller-manager` from Controller Manager, and Cloud Controller's logic was decoupled.
* v1.11 saw the External Cloud Provider upgrade to Beta.

Creating a new Cloud Provider for a new cloud supplier entails:

* Writing a cloud provider code that implements [cloudprovider.Interface](https://github.com/kubernetes/cloud-provider/blob/master/cloud.go).
* Linking the cloud provider to `cloud-controller-manager`.
  * Import the new cloud provider into `cloud-controller-manager`: `import "pkg/new-cloud-provider"`.
  * Pass the name of the new cloud provider at initialization, such as `cloudprovider.InitCloudProvider("rancher", s.CloudConfigFile)`.
* Configuring the kube-controller-manager by `--cloud-provider=external`.
* Starting the `cloud-controller-manager`.

Further guidance and detailed implementation can be found at [rancher-cloud-controller-manager](https://github.com/rancher/rancher-cloud-controller-manager) and [cloud-controller-manager](https://github.com/kubernetes/cloud-provider).


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://kubernetes.feisky.xyz/en/extension/cloud-provider.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.