Using Node Authorization

Node authorization is a special-purpose authorization mode that specifically authorizes API requests made by kubelets.

Overview

The Node authorizer allows a kubelet to perform API operations. This includes:

Read operations:

  • services
  • endpoints
  • nodes
  • pods
  • secrets, configmaps, persistent volume claims and persistent volumes related to pods bound to the kubelet’s node

Write operations:

  • nodes and node status (enable the NodeRestriction admission plugin to limit a kubelet to modify its own node)
  • pods and pod status (enable the NodeRestriction admission plugin to limit a kubelet to modify pods bound to itself)
  • events

Auth-related operations:

  • read/write access to the CertificateSigningRequests API for TLS bootstrapping
  • the ability to create TokenReviews and SubjectAccessReviews for delegated authentication/authorization checks

In future releases, the node authorizer may add or remove permissions to ensure kubelets have the minimal set of permissions required to operate correctly.

In order to be authorized by the Node authorizer, kubelets must use a credential that identifies them as being in the system:nodes group, with a username of system:node:<nodeName>. This group and user name format match the identity created for each kubelet as part of kubelet TLS bootstrapping.

The value of <nodeName> must match precisely the name of the node as registered by the kubelet. By default, this is the host name as provided by hostname, or overridden via the kubelet option --hostname-override. However, when using the --cloud-provider kubelet option, the specific hostname may be determined by the cloud provider, ignoring the local hostname and the --hostname-override option. For specifics about how the kubelet determines the hostname, see the kubelet options reference.

To enable the Node authorizer, start the apiserver with --authorization-mode=Node.

To limit the API objects kubelets are able to write, enable the NodeRestriction admission plugin by starting the apiserver with --enable-admission-plugins=...,NodeRestriction,...

Migration considerations

Kubelets outside the system:nodes group

Kubelets outside the system:nodes group would not be authorized by the Node authorization mode, and would need to continue to be authorized via whatever mechanism currently authorizes them. The node admission plugin would not restrict requests from these kubelets.

Kubelets with undifferentiated usernames

In some deployments, kubelets have credentials that place them in the system:nodes group, but do not identify the particular node they are associated with, because they do not have a username in the system:node:... format. These kubelets would not be authorized by the Node authorization mode, and would need to continue to be authorized via whatever mechanism currently authorizes them.

The NodeRestriction admission plugin would ignore requests from these kubelets, since the default node identifier implementation would not consider that a node identity.

Upgrades from previous versions using RBAC

Upgraded pre-1.7 clusters using RBAC will continue functioning as-is because the system:nodes group binding will already exist.

If a cluster admin wishes to start using the Node authorizer and NodeRestriction admission plugin to limit node access to the API, that can be done non-disruptively:

  1. Enable the Node authorization mode (--authorization-mode=Node,RBAC) and the NodeRestriction admission plugin
  2. Ensure all kubelets’ credentials conform to the group/username requirements
  3. Audit apiserver logs to ensure the Node authorizer is not rejecting requests from kubelets (no persistent NODE DENY messages logged)
  4. Delete the system:node cluster role binding

RBAC Node Permissions

In 1.6, the system:node cluster role was automatically bound to the system:nodes group when using the RBAC Authorization mode.

In 1.7, the automatic binding of the system:nodes group to the system:node role is deprecated because the node authorizer accomplishes the same purpose with the benefit of additional restrictions on secret and configmap access. If the Node and RBAC authorization modes are both enabled, the automatic binding of the system:nodes group to the system:node role is not created in 1.7.

In 1.8, the binding will not be created at all.

When using RBAC, the system:node cluster role will continue to be created, for compatibility with deployment methods that bind other users or groups to that role.