kubelet authnz

docs/admin/index.md

@@ -88,3 +88,4 @@ project](/docs/admin/salt).
 * **Securing the kubelet**
   * [Master-Node communication](/docs/admin/master-node-communication/)
   * [TLS bootstrapping](/docs/admin/kubelet-tls-bootstrapping/)
+  * [Kubelet authentication/authorization](/docs/admin/kubelet-authentication-authorization/)

docs/admin/kubelet-authentication-authorization.md

@@ -0,0 +1,79 @@
+---
+assignees:
+- liggitt
+
+---
+
+* TOC
+{:toc}
+
+## Summary
+
+The kubelet's HTTPS endpoint exposes APIs which give access to data of varying sensitivity,
+and allow performing operations of varying 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:
+* start the kubelet with the `--anonymous-auth=false` flag
+
+To enable X509 client certificate authentication to the kubelet's HTTPS endpoint:
+* start the kubelet with the `--client-ca-file` flag, providing a CA bundle to verify client certificates with 
+* start the apiserver with `--kubelet-client-certificate` and `--kubelet-client-key` flags
+* see the [apiserver authentication documentation](/docs/admin/authentication/#x509-client-certs) 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/v1beta1` API group is enabled in the API server
+* start the kubelet with the `--authentication-token-webhook`, `--kubeconfig`, and `--require-kubeconfig` flags
+* the kubelet calls the `TokenReview` API on the configured API server to determine user information from bearer tokens 
+
+## Kubelet authorization
+
+Any request that passes authentication (including anonymous requests) 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/v1beta1` API group is enabled in the API server
+* start the kubelet with the `--authorization-mode=Webhook`, `--kubeconfig`, and `--require-kubeconfig` flags
+* the kubelet calls the `SubjectAccessReview` API on the configured API server to determine whether each request is authorized 
+
+The kubelet authorizes API requests using the same [request attributes](/docs/admin/authorization/#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 

docs/admin/master-node-communication.md

@@ -23,7 +23,11 @@ All communication paths from the cluster to the master terminate at the
 apiserver (none of the other master components are designed to expose remote
 services). In a typical deployment, the apiserver is configured to listen for
 remote connections on a secure HTTPS port (443) with one or more forms of
-client [authentication](/docs/admin/authentication/) enabled.
+client [authentication](/docs/admin/authentication/) enabled. One or more forms
+of [authorization](/docs/admin/authorization/) should be enabled, especially
+if [anonymous requests](/docs/admin/authentication/#anonymous-requests) or 
+[service account tokens](/docs/admin/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
@@ -58,16 +62,29 @@ cluster. The first is from the apiserver to the kubelet process which runs on
 each node in the cluster. The second is from the apiserver to any node, pod,
 or service through the apiserver's proxy functionality.
 
+### apiserver -> kubelet
+
 The connections from the apiserver to the kubelet are used for fetching logs
 for pods, attaching (through kubectl) to running pods, and using the kubelet's
-port-forwarding functionality. These connections terminate at the kubelet's
-HTTPS endpoint, which is typically using a self-signed certificate, and
-ignore the certificate presented by the kubelet (although you can override this
-behavior by specifying the `--kubelet-certificate-authority`,
-`--kubelet-client-certificate`, and `--kubelet-client-key` flags when starting
-the cluster apiserver). By default, these connections **are not currently safe**
-to run over untrusted and/or public networks as they are subject to
-man-in-the-middle attacks.
+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.
+
+To verify this connection, use the `--kubelet-certificate-authority` flag to 
+provide the apiserver with a root certificates bundle to use to verify the 
+kubelet's serving certificate.
+
+If that is not possible, use [SSH tunneling](/docs/admin/master-node-communication/#ssh-tunnels)
+between the apiserver and kubelet if required to avoid connecting over an 
+untrusted or public network.
+
+Finally, [Kubelet authentication and/or authorization](/docs/admin/kubelet-authentication-authorization/)
+should be enabled to secure the kubelet API. 
+
+### apiserver -> 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