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Updates to docs/admin/kubelet-tls-bootstrapping (#3617)

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* update TLS bootstrapping doc

* formatting edits on top of prev edits

* revert to lowercase b in title
This commit is contained in:
Murad Korejo
2017-06-22 16:22:20 -05:00
committed by Andrew Chen
parent 6283e51faa
commit bbffb34c6c
1 changed files with 52 additions and 52 deletions
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docs/admin/kubelet-tls-bootstrapping.md
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@@ -10,21 +10,17 @@ title: TLS bootstrapping
## Overview ## Overview
This document describes how to set up TLS client certificate bootstrapping for kubelets. This document describes how to set up TLS client certificate bootstrapping for kubelets.
Kubernetes 1.4 introduces an experimental API for requesting certificates from a cluster-level Kubernetes 1.4 introduced an API for requesting certificates from a cluster-level Certificate Authority (CA). The original intent of this API is to enable provisioning of TLS client certificates for kubelets. The proposal can be found [here](https://github.com/kubernetes/kubernetes/pull/20439)
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). and progress on the feature is being tracked as [feature #43](https://github.com/kubernetes/features/issues/43).
## apiserver configuration ## kube-apiserver configuration
You must provide a token file which specifies at least one "bootstrap token" assigned to a kubelet bootstrap-specific group. You must provide a token file which specifies at least one "bootstrap token" assigned to a kubelet bootstrap-specific group.
This group will later be used in the controller-manager configuration to scope approvals in the default approval 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 controller. As this feature matures, you should ensure tokens are bound to a Role-Based Access Control (RBAC) policy which limits requests
using the bootstrap token to only be able to make requests related to certificate provisioning. When RBAC policy (using the bootstrap token) strictly to client requests related to certificate provisioning. With RBAC in place, scoping the tokens to a group allows for great flexibility (e.g. you could disable a particular bootstrap group's access when you are done provisioning the nodes).
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).
### Token auth file ### Token authentication file
Tokens are arbitrary but should represent at least 128 bits of entropy derived from a secure random number 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: generator (such as /dev/urandom on most modern systems). There are multiple ways you can generate a token. For example:
@@ -32,54 +28,60 @@ generator (such as /dev/urandom on most modern systems). There are multiple ways
will generate tokens that look like `02b50b05283e98dd0fd71db496ef01e8` will generate tokens that look like `02b50b05283e98dd0fd71db496ef01e8`
The token file will look like the following example, where the first three values can be anything and the quoted group The token file should look like the following example, where the first three values can be anything and the quoted group
name should be as depicted: name should be as depicted:
``` ```
02b50b05283e98dd0fd71db496ef01e8,kubelet-bootstrap,10001,"system:kubelet-bootstrap" 02b50b05283e98dd0fd71db496ef01e8,kubelet-bootstrap,10001,"system:kubelet-bootstrap"
``` ```
Add the `--token-auth-file=FILENAME` flag to the apiserver command to enable the token file. Add the `--token-auth-file=FILENAME` flag to the kube-apiserver command (in your systemd unit file perhaps) to enable the token file.
See docs at http://kubernetes.io/docs/admin/authentication/#static-token-file for further details. See docs [here](http://kubernetes.io/docs/admin/authentication/#static-token-file) for further details.
### Client certificate CA bundle ### Client certificate CA bundle
Add the `--client-ca-file=FILENAME` flag to the apiserver command to enable client certificate authentication, Add the `--client-ca-file=FILENAME` flag to the kube-apiserver command to enable client certificate authentication,
referencing a certificate authority bundle containing the signing certificate. referencing a certificate authority bundle containing the signing certificate (e.g. `--client-ca-file=/var/lib/kubernetes/ca.pem`).
## controller-manager configuration ## kube-controller-manager configuration
The API for requesting certificates adds a certificate-issuing control loop to the KCM. This takes the form of a The API for requesting certificates adds a certificate-issuing control loop to the Kubernetes Controller Manager. This takes the form of a
[cfssl](https://blog.cloudflare.com/introducing-cfssl/) local signer using assets on disk. [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.
Currently, all certificates issued have one year validity and a default set of key usages.
### Signing assets ### Signing assets
You must provide a Certificate Authority in order to provide the cryptographic materials necessary to issue certificates. 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 This CA should be trusted by kube-apiserver for authentication with the `--client-ca-file=FILENAME` 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. 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. Both certificate and key are assumed to be PEM-encoded.
The new controller-manager flags are: The kube-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" --cluster-signing-cert-file="/etc/path/to/kubernetes/ca/ca.crt" --cluster-signing-key-file="/etc/path/to/kubernetes/ca/ca.key"
``` ```
### Auto-approval ### Automatic approval
To ease deployment and testing, the alpha version of the certificate request API includes a flag to approve all certificate To ease deployment and testing, there is an experimental flag in the certificate bootstrapping API 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 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 token in the token file above. Use of this flag circumvents the approval process described below and is not recommended
for production use. for production use.
The flag is: The flag is:
``` ```
--insecure-experimental-approve-all-kubelet-csrs-for-group="system:kubelet-bootstrap" --insecure-experimental-approve-all-kubelet-csrs-for-group="system:kubelet-bootstrap"
``` ```
## kubelet configuration ## 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 To request a client certificate from kube-apiserver, the kubelet first 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 bootstrap authentication token. You can use `kubectl config set-cluster`, `set-credentials`, and `set-context` to build this kubeconfig. Provide the name `kubelet-bootstrap` to `kubectl config set-credentials` and include `--token=<token-value>` as follows:
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: kubectl config set-credentials kubelet-bootstrap --token=${BOOTSTRAP_TOKEN} --kubeconfig=bootstrap.kubeconfig
```
When starting the kubelet, if the file specified by `--kubeconfig` does not exist, the bootstrap kubeconfig is used to request a client certificate from the API server. On approval of the certificate request and receipt back by the kubelet, 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 placed in the directory specified by `--cert-dir`.
The flag to enable this bootstrapping when starting the kubelet is:
``` ```
--experimental-bootstrap-kubeconfig="/path/to/bootstrap/kubeconfig" --experimental-bootstrap-kubeconfig="/path/to/bootstrap/kubeconfig"
@@ -89,8 +91,6 @@ by `--cert-dir`. The new flag is:
The signing controller does not immediately sign all certificate requests. Instead, it waits until they have been flagged with an 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 "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. 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 An administrator can list CSRs with `kubectl get csr` and describe one in detail with `kubectl describe csr <name>`. Before the 1.6 release there were
[currently no direct approve/deny commands](https://github.com/kubernetes/kubernetes/issues/30163) so an approver will need to update [no direct approve/deny commands](https://github.com/kubernetes/kubernetes/issues/30163) so an approver had 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 the Status field directly ([rough how-to](https://github.com/gtank/csrctl)). Later versions of Kubernetes offer `kubectl certificate approve <name>` and `kubectl certificate deny <name>` commands.
at [https://github.com/gtank/csrctl](https://github.com/gtank/csrctl).