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| --- | ||
| assignees: | ||
| - mikedanese | ||
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| --- | ||
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| * TOC | ||
| {:toc} | ||
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| ## Summary | ||
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| This document describes setting up TLS client certificate bootstrapping for kubelets. | ||
| Kubernetes 1.4 introduces an experimental API for requesting certificates from a cluster-level | ||
| Certificate Authority (CA). The first supported use of this API is the provisioning of TLS client | ||
| certificates for kubelets. The proposal can be found [here](https://github.com/kubernetes/kubernetes/pull/20439) | ||
| and progress on the feature is being tracked as [feature #43](https://github.com/kubernetes/features/issues/43). | ||
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| ## apiserver configuration | ||
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| You must provide a token file which specifies at least one "bootstrap token" assigned to a kubelet boostrap-specific group. | ||
| This group will later be used in the controller-manager configuration to scope approvals in the default approval | ||
| controller. As this feature matures, you should ensure tokens are bound to an RBAC policy which limits requests | ||
| using the bootstrap token to only be able to make requests related to certificate provisioning. When RBAC policy | ||
| is in place, scoping the tokens to a group will allow great flexibility (e.g. you could disable a particular | ||
| bootstrap group's access when you are done provisioning the nodes). | ||
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| ### Token auth file | ||
| Tokens are arbitrary but should represent at least 128 bits of entropy derived from a secure random number | ||
| generator (such as /dev/urandom on most modern systems). There are multiple ways you can generate a token. For example: | ||
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| `head -c 16 /dev/urandom | od -An -t x | tr -d ' '` | ||
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| will generate tokens that look like `02b50b05283e98dd0fd71db496ef01e8` | ||
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| The token file will look like the following example, where the first three values can be anything and the quoted group | ||
| name should be as depicted: | ||
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| ``` | ||
| 02b50b05283e98dd0fd71db496ef01e8,kubelet-bootstrap,10001,"system:kubelet-bootstrap" | ||
| ``` | ||
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| Add the `--token-auth-file=FILENAME` flag to the apiserver command to enable the token file. | ||
| See docs at http://kubernetes.io/docs/admin/authentication/#static-token-file for further details. | ||
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| ### Client certificate CA bundle | ||
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| Add the `--client-ca-file=FILENAME` flag to the apiserver command to enable client certificate authentication, | ||
| referencing a certificate authority bundle containing the signing certificate. | ||
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| ## controller-manager configuration | ||
| The API for requesting certificates adds a certificate-issuing control loop to the KCM. This takes the form of a | ||
| [cfssl](https://blog.cloudflare.com/introducing-cfssl/) local signer using assets on disk. | ||
| Currently, all certificates issued have one year validity and a default set of key usages. | ||
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| ### Signing assets | ||
| You must provide a Certificate Authority in order to provide the cryptographic materials necessary to issue certificates. | ||
| This CA should be trusted by the apiserver for authentication with the `--client-ca-file=SOMEFILE` flag. The management | ||
| of the CA is beyond the scope of this document but it is recommended that you generate a dedicated CA for Kubernetes. | ||
| Both certificate and key are assumed to be PEM-encoded. | ||
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| The new controller-manager flags are: | ||
| ``` | ||
| --cluster-signing-cert-file="/etc/path/to/kubernetes/ca/ca.crt" --cluster-signing-key-file="/etc/path/to/kubernetes/ca/ca.key" | ||
| ``` | ||
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| ### Auto-approval | ||
| To ease deployment and testing, the alpha version of the certificate request API includes a flag to approve all certificate | ||
| requests made by users in a certain group. The intended use of this is to whitelist only the group corresponding to the bootstrap | ||
| token in the token file above. Use of this flag circumvents makes the "approval" process described below and is not recommended | ||
| for production use. | ||
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| The flag is: | ||
| ``` | ||
| --insecure-experimental-approve-all-kubelet-csrs-for-group="system:kubelet-bootstrap" | ||
| ``` | ||
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| ## kubelet configuration | ||
| To use request a client cert from the certificate request API, the kubelet needs a path to a kubeconfig file that contains the | ||
| bootstrap auth token. If the file specified by `--kubeconfig` does not exist, the bootstrap kubeconfig is used to request a | ||
| client certificate from the API server. On success, a kubeconfig file referencing the generated key and obtained certificate | ||
| is written to the path specified by `--kubeconfig`. The certificate and key file will be stored in the directory pointed | ||
| by `--cert-dir`. The new flag is: | ||
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| ``` | ||
| --experimental-bootstrap-kubeconfig="/path/to/bootstrap/kubeconfig" | ||
| ``` | ||
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| ## kubectl approval | ||
| The signing controller does not immediately sign all certificate requests. Instead, it waits until they have been flagged with an | ||
| "Approved" status by an appropriately-privileged user. This is intended to eventually be an automated process handled by an external | ||
| approval controller, but for the alpha version of the API it can be done manually by a cluster administrator using kubectl. | ||
| An administrator can list CSRs with `kubectl get csr`, describe one in detail with `kubectl describe <name>`. There are | ||
| [currently no direct approve/deny commands](https://github.com/kubernetes/kubernetes/issues/30163) so an approver will need to update | ||
| the Status field directly. A rough example of how to do this in bash which should only be used until the porcelain merges is available | ||
| at https://github.com/gtank/csrctl. | ||
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