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Node Authorization

Node Authorization Service

:warning: The node authorization service is deprecated. As of Kubernetes 1.19 kops will, on AWS, ignore the nodeAuthorization field of the cluster spec and worker nodes will obtain client certificates for kubelet and other purposes through kops-controller.

The [node authorization service] is an experimental service which in the absence of a kops-apiserver provides the distribution of tokens to the worker nodes. Bootstrap tokens provide worker nodes a short-time credential to request access kubeconfig certificate. A gist of the flow is;

  • a secret of type bootstrap.kubernetes.io/token is created on behalf of a node in the kube-system namespace.
  • the token is distributed to the node by some means and then used as the bearer token of the initial request to the kubernetes api.
  • the token itself is bound to the cluster role which grants permission to generate a CSR, an additional cluster role provides access for the controller to auto-approve this CSR requests as well.
  • two certificates are generated by the kubelet using bootstrap process, one for the kubelet api and the other a client certificate to the kubelet itself.
  • the client certificate by default is added into the system:nodes rbac group (note, if you are using PSP this is automatically bound by kops on your behalf).
  • the kubelet at this point has a server certificate and the client api certificate and good to go.

Integration with Kops

The node authorization service is run on the master as a daemonset, by default dns is node-authorizer-internal.dns_zone:10443 and added via same mechanism at the internal kube-apiserver i.e. annotations on the kube-apiserver pods which is picked up the dns-controller and added to the dns zone.

When the node authorization service is enabled a systemd (node-authorizer.service) unit is added on the worker nodes. This runs the node-authorizer in client mode and connects to the authorization service requesting a bootstrap token.

Authorizers

The node authorizer currently supports two authorizers; aws and alwaysallow. The latter is self-explanatory, as for the aws authorizer, in order for a request to be authorized the following checks are performed.

  • the worker node retrieves the pkcs7 signed instance document from the metadata service; this is unique for each instance and available only to them.
  • the client connects using a client certificate which is first checked and passes the instance document to the authorization service.
  • the signed instance document is validated against the public certificates from AWS.
  • we check the node exists and is running.
  • we check the node is running in our region.
  • we check the node is running in our vpc.
  • we check the node is tagged with the correct kubernetes tag.
  • we check the ip address of the client requesting the document is the same the instance document.
  • we check that the node has not already registered.

Assuming all the conditions are met a secret token is generated and returned to the client to continue the providing of the worker node.

Enabling the Node Authorization Service

Enabling the node authorization service is as follows; firstly you must enable the feature flag as node authorization is still experimental; export KOPS_FEATURE_FLAGS=EnableNodeAuthorization

# in the cluster spec
nodeAuthorization:
  # enable the service under the node authorization section, please review the settings in the components.go
  nodeAuthorizer: {}

Note, by default this will also switch on the Node authorization and RBAC mode. We would also suggest turning on the NodeRestriction admission controller.