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Merge pull request #32518 from liggitt/kubelet-auth-proposal
Automatic merge from submit-queue Proposal: kubelet authentication/authorization Proposal for kubernetes/enhancements#89
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| <!-- BEGIN MUNGE: UNVERSIONED_WARNING --> | ||
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| <!-- BEGIN STRIP_FOR_RELEASE --> | ||
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| <img src="http://kubernetes.io/kubernetes/img/warning.png" alt="WARNING" | ||
| width="25" height="25"> | ||
| <img src="http://kubernetes.io/kubernetes/img/warning.png" alt="WARNING" | ||
| width="25" height="25"> | ||
| <img src="http://kubernetes.io/kubernetes/img/warning.png" alt="WARNING" | ||
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| <img src="http://kubernetes.io/kubernetes/img/warning.png" alt="WARNING" | ||
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| <img src="http://kubernetes.io/kubernetes/img/warning.png" alt="WARNING" | ||
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| <h2>PLEASE NOTE: This document applies to the HEAD of the source tree</h2> | ||
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| If you are using a released version of Kubernetes, you should | ||
| refer to the docs that go with that version. | ||
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| Documentation for other releases can be found at | ||
| [releases.k8s.io](http://releases.k8s.io). | ||
| </strong> | ||
| -- | ||
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| <!-- END STRIP_FOR_RELEASE --> | ||
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| <!-- END MUNGE: UNVERSIONED_WARNING --> | ||
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| # Kubelet Authentication / Authorization | ||
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| Author: Jordan Liggitt ([email protected]) | ||
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| ## Overview | ||
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| The kubelet exposes endpoints which give access to data of varying sensitivity, | ||
| and allow performing operations of varying power on the node and within containers. | ||
| There is no built-in way to limit or subdivide access to those endpoints, | ||
| so deployers must secure the kubelet API using external, ad-hoc methods. | ||
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| This document proposes a method for authenticating and authorizing access | ||
| to the kubelet API, using interfaces and methods that complement the existing | ||
| authentication and authorization used by the API server. | ||
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| ## Preliminaries | ||
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| This proposal assumes the existence of: | ||
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| * a functioning API server | ||
| * the SubjectAccessReview and TokenReview APIs | ||
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| It also assumes each node is additionally provisioned with the following information: | ||
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| 1. Location of the API server | ||
| 2. Any CA certificates necessary to trust the API server's TLS certificate | ||
| 3. Client credentials authorized to make SubjectAccessReview and TokenReview API calls | ||
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| ## API Changes | ||
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| None | ||
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| ## Kubelet Authentication | ||
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| Enable starting the kubelet with one or more of the following authentication methods: | ||
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| * x509 client certificate | ||
| * bearer token | ||
| * anonymous (current default) | ||
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| For backwards compatibility, the default is to enable anonymous authentication. | ||
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| ### x509 client certificate | ||
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| Add a new `--client-ca-file=[file]` option to the kubelet. | ||
| When started with this option, the kubelet authenticates incoming requests using x509 | ||
| client certificates, validated against the root certificates in the provided bundle. | ||
| The kubelet will reuse the x509 authenticator already used by the API server. | ||
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| The master API server can already be started with `--kubelet-client-certificate` and | ||
| `--kubelet-client-key` options in order to make authenticated requests to the kubelet. | ||
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| ### Bearer token | ||
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| Add a new `--authentication-token-webhook=[true|false]` option to the kubelet. | ||
| When true, the kubelet authenticates incoming requests with bearer tokens by making | ||
| `TokenReview` API calls to the API server. | ||
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| The kubelet will reuse the webhook authenticator already used by the API server, configured | ||
| to call the API server using the connection information already provided to the kubelet. | ||
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| To improve performance of repeated requests with the same bearer token, the | ||
| `--authentication-token-webhook-cache-ttl` option supported by the API server | ||
| would be supported. | ||
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| ### Anonymous | ||
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| Add a new `--anonymous-auth=[true|false]` option to the kubelet. | ||
| When true, requests to the secure port 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`. | ||
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| ## Kubelet Authorization | ||
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| Add a new `--authorization-mode` option to the kubelet, specifying one of the following modes: | ||
| * `Webhook` | ||
| * `AlwaysAllow` (current default) | ||
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| For backwards compatibility, the authorization mode defaults to `AlwaysAllow`. | ||
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| ### Webhook | ||
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| Webhook mode converts the request to authorization attributes, and makes a `SubjectAccessReview` | ||
| API call to check if the authenticated subject is allowed to make a request with those attributes. | ||
| This enables authorization policy to be centrally managed by the authorizer configured for the API server. | ||
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| The kubelet will reuse the webhook authorizer already used by the API server, configured | ||
| to call the API server using the connection information already provided to the kubelet. | ||
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| To improve performance of repeated requests with the same authenticated subject and request attributes, | ||
| the same webhook authorizer caching options supported by the API server would be supported: | ||
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| * `--authorization-webhook-cache-authorized-ttl` | ||
| * `--authorization-webhook-cache-unauthorized-ttl` | ||
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| ### AlwaysAllow | ||
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| This mode allows any authenticated request. | ||
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| ## Future Work | ||
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| * Add support for CRL revocation for x509 client certificate authentication (http://issue.k8s.io/18982) | ||
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