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Update control-plane-node-communication.md 

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@ -11,14 +11,14 @@ aliases:
<!-- overview --> <!-- overview -->
This document catalogs the communication paths between the control plane (really the apiserver) and the Kubernetes cluster. The intent is to allow users to customize their installation to harden the network configuration such that the cluster can be run on an untrusted network (or on fully public IPs on a cloud provider). This document catalogs the communication paths between the control plane (apiserver) and the Kubernetes cluster. The intent is to allow users to customize their installation to harden the network configuration such that the cluster can be run on an untrusted network (or on fully public IPs on a cloud provider).
<!-- body --> <!-- body -->
## Node to Control Plane ## Node to Control Plane
Kubernetes has a "hub-and-spoke" API pattern. All API usage from nodes (or the pods they run) terminate at the apiserver (none of the other control plane components are designed to expose remote services). The apiserver is configured to listen for remote connections on a secure HTTPS port (typically 443) with one or more forms of client [authentication](/docs/reference/access-authn-authz/authentication/) enabled. Kubernetes has a "hub-and-spoke" API pattern. All API usage from nodes (or the pods they run) terminates at the apiserver. None of the other control plane components are designed to expose remote services. The apiserver is configured to listen for remote connections on a secure HTTPS port (typically 443) with one or more forms of client [authentication](/docs/reference/access-authn-authz/authentication/) enabled.
One or more forms of [authorization](/docs/reference/access-authn-authz/authorization/) should be enabled, especially if [anonymous requests](/docs/reference/access-authn-authz/authentication/#anonymous-requests) or [service account tokens](/docs/reference/access-authn-authz/authentication/#service-account-tokens) are allowed. One or more forms of [authorization](/docs/reference/access-authn-authz/authorization/) should be enabled, especially if [anonymous requests](/docs/reference/access-authn-authz/authentication/#anonymous-requests) or [service account tokens](/docs/reference/access-authn-authz/authentication/#service-account-tokens) are allowed.
Nodes should be provisioned with the public root certificate for the cluster such that they can connect securely to the apiserver along with valid client credentials. A good approach is that the client credentials provided to the kubelet are in the form of a client certificate. See [kubelet TLS bootstrapping](/docs/reference/command-line-tools-reference/kubelet-tls-bootstrapping/) for automated provisioning of kubelet client certificates. Nodes should be provisioned with the public root certificate for the cluster such that they can connect securely to the apiserver along with valid client credentials. A good approach is that the client credentials provided to the kubelet are in the form of a client certificate. See [kubelet TLS bootstrapping](/docs/reference/command-line-tools-reference/kubelet-tls-bootstrapping/) for automated provisioning of kubelet client certificates.
@ -42,7 +42,7 @@ The connections from the apiserver to the kubelet are used for:
* Attaching (through kubectl) to running pods. * Attaching (through kubectl) to running pods.
* Providing the kubelet's port-forwarding functionality. * Providing the kubelet's port-forwarding functionality.
These connections terminate at the kubelet's HTTPS endpoint. By default, the apiserver does not verify the kubelet's serving certificate, which makes the connection subject to man-in-the-middle attacks, and **unsafe** to run over untrusted and/or public networks. These connections terminate at the kubelet's HTTPS endpoint. By default, the apiserver does not verify the kubelet's serving certificate, which makes the connection subject to man-in-the-middle attacks and **unsafe** to run over untrusted and/or public networks.
To verify this connection, use the `--kubelet-certificate-authority` flag to provide the apiserver with a root certificate bundle to use to verify the kubelet's serving certificate. To verify this connection, use the `--kubelet-certificate-authority` flag to provide the apiserver with a root certificate bundle to use to verify the kubelet's serving certificate.
@ -53,20 +53,20 @@ Finally, [Kubelet authentication and/or authorization](/docs/reference/command-l
### apiserver to nodes, pods, and services ### apiserver to nodes, pods, and services
The connections from the apiserver to a node, pod, or service default to plain HTTP connections and are therefore neither authenticated nor encrypted. They can be run over a secure HTTPS connection by prefixing `https:` to the node, pod, or service name in the API URL, but they will not validate the certificate provided by the HTTPS endpoint nor provide client credentials so while the connection will be encrypted, it will not provide any guarantees of integrity. These connections **are not currently safe** to run over untrusted and/or public networks. The connections from the apiserver to a node, pod, or service default to plain HTTP connections and are therefore neither authenticated nor encrypted. They can be run over a secure HTTPS connection by prefixing `https:` to the node, pod, or service name in the API URL, but they will not validate the certificate provided by the HTTPS endpoint nor provide client credentials. So while the connection will be encrypted, it will not provide any guarantees of integrity. These connections **are not currently safe** to run over untrusted or public networks.
### SSH tunnels ### SSH tunnels
Kubernetes supports SSH tunnels to protect the control plane to nodes communication paths. In this configuration, the apiserver initiates an SSH tunnel to each node in the cluster (connecting to the ssh server listening on port 22) and passes all traffic destined for a kubelet, node, pod, or service through the tunnel. Kubernetes supports SSH tunnels to protect the control plane to nodes communication paths. In this configuration, the apiserver initiates an SSH tunnel to each node in the cluster (connecting to the ssh server listening on port 22) and passes all traffic destined for a kubelet, node, pod, or service through the tunnel.
This tunnel ensures that the traffic is not exposed outside of the network in which the nodes are running. This tunnel ensures that the traffic is not exposed outside of the network in which the nodes are running.
SSH tunnels are currently deprecated so you shouldn't opt to use them unless you know what you are doing. The Konnectivity service is a replacement for this communication channel. SSH tunnels are currently deprecated, so you shouldn't opt to use them unless you know what you are doing. The Konnectivity service is a replacement for this communication channel.
### Konnectivity service ### Konnectivity service
{{< feature-state for_k8s_version="v1.18" state="beta" >}} {{< feature-state for_k8s_version="v1.18" state="beta" >}}
As a replacement to the SSH tunnels, the Konnectivity service provides TCP level proxy for the control plane to cluster communication. The Konnectivity service consists of two parts: the Konnectivity server and the Konnectivity agents, running in the control plane network and the nodes network respectively. The Konnectivity agents initiate connections to the Konnectivity server and maintain the network connections. As a replacement to the SSH tunnels, the Konnectivity service provides TCP level proxy for the control plane to cluster communication. The Konnectivity service consists of two parts: the Konnectivity server in the control plane network and the Konnectivity agents in the nodes network. The Konnectivity agents initiate connections to the Konnectivity server and maintain the network connections.
After enabling the Konnectivity service, all control plane to nodes traffic goes through these connections. After enabling the Konnectivity service, all control plane to nodes traffic goes through these connections.
Follow the [Konnectivity service task](/docs/tasks/extend-kubernetes/setup-konnectivity/) to set up the Konnectivity service in your cluster. Follow the [Konnectivity service task](/docs/tasks/extend-kubernetes/setup-konnectivity/) to set up the Konnectivity service in your cluster.