Kubelet authentication/authorization
Overview
A kubelet’s HTTPS endpoint exposes APIs which give access to data of varying sensitivity, and allow you to perform operations with varying levels of power on the node and within containers.
This document describes how to authenticate and authorize access to the kubelet’s HTTPS endpoint.
Kubelet authentication
By default, requests to the kubelet’s HTTPS endpoint that are not rejected by other configured
authentication methods are treated as anonymous requests, and given a username of system:anonymous
and a group of system:unauthenticated.
To disable anonymous access and send 401 Unauthorized responses to unauthenticated requests:
- start the kubelet with the
--anonymous-auth=falseflag
To enable X509 client certificate authentication to the kubelet’s HTTPS endpoint:
- start the kubelet with the
--client-ca-fileflag, providing a CA bundle to verify client certificates with - start the apiserver with
--kubelet-client-certificateand--kubelet-client-keyflags - see the apiserver authentication documentation for more details
To enable API bearer tokens (including service account tokens) to be used to authenticate to the kubelet’s HTTPS endpoint:
- ensure the
authentication.k8s.io/v1beta1API group is enabled in the API server - start the kubelet with the
--authentication-token-webhook,--kubeconfig, and--require-kubeconfigflags - the kubelet calls the
TokenReviewAPI on the configured API server to determine user information from bearer tokens
Kubelet authorization
Any request that is successfully authenticated (including an anonymous request) is then authorized. The default authorization mode is AlwaysAllow, which allows all requests.
There are many possible reasons to subdivide access to the kubelet API:
- anonymous auth is enabled, but anonymous users’ ability to call the kubelet API should be limited
- bearer token auth is enabled, but arbitrary API users’ (like service accounts) ability to call the kubelet API should be limited
- client certificate auth is enabled, but only some of the client certificates signed by the configured CA should be allowed to use the kubelet API
To subdivide access to the kubelet API, delegate authorization to the API server:
- ensure the
authorization.k8s.io/v1beta1API group is enabled in the API server - start the kubelet with the
--authorization-mode=Webhook,--kubeconfig, and--require-kubeconfigflags - the kubelet calls the
SubjectAccessReviewAPI on the configured API server to determine whether each request is authorized
The kubelet authorizes API requests using the same request attributes approach as the apiserver.
The verb is determined from the incoming request’s HTTP verb:
| HTTP verb | request verb |
|---|---|
| POST | create |
| GET, HEAD | get |
| PUT | update |
| PATCH | patch |
| DELETE | delete |
The resource and subresource is determined from the incoming request’s path:
| Kubelet API | resource | subresource |
|---|---|---|
| /stats/* | nodes | stats |
| /metrics/* | nodes | metrics |
| /logs/* | nodes | log |
| /spec/* | nodes | spec |
| all others | nodes | proxy |
The namespace and API group attributes are always an empty string, and
the resource name is always the name of the kubelet’s Node API object.
When running in this mode, ensure the user identified by the --kubelet-client-certificate and --kubelet-client-key
flags passed to the apiserver is authorized for the following attributes:
- verb=*, resource=nodes, subresource=proxy
- verb=*, resource=nodes, subresource=stats
- verb=*, resource=nodes, subresource=log
- verb=*, resource=nodes, subresource=spec
- verb=*, resource=nodes, subresource=metrics