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
NodeRestrictionadmission plugin to limit a kubelet to modify its own node) - pods and pod status (enable the
NodeRestrictionadmission plugin to limit a kubelet to modify pods bound to itself) - events
Auth-related operations:
- read/write access to the certificationsigningrequests 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.
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 --admission-control=...,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:
- Enable the
Nodeauthorization mode (--authorization-mode=Node,RBAC) and theNodeRestrictionadmission plugin - Ensure all kubelets’ credentials conform to the group/username requirements
- Audit apiserver logs to ensure the
Nodeauthorizer is not rejecting requests from kubelets (no persistentNODE DENYmessages logged) - Delete the
system:nodecluster 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.