315 lines
13 KiB
Markdown
315 lines
13 KiB
Markdown
---
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assignees:
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- mikedanese
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- thockin
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---
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Authentication in kubernetes can differ for different individuals.
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- A running kubelet might have one way of authenticating (i.e. certificates).
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- Users might have a different way of authenticating (i.e. tokens).
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- Administrators might have a list of certificates which they provide individual users.
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- There may be multiple clusters, and we may want to define them all in one place - giving users the ability to use their own certificates and reusing the same global configuration.
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So in order to easily switch between multiple clusters, for multiple users, a kubeconfig file was defined.
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This file contains a series of authentication mechanisms and cluster connection information associated with nicknames. It also introduces the concept of a tuple of authentication information (user) and cluster connection information called a context that is also associated with a nickname.
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Multiple kubeconfig files are allowed, if specified explicitly. At runtime they are loaded and merged along with override options specified from the command line (see [rules](#loading-and-merging) below).
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## Related discussion
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http://issue.k8s.io/1755
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## Components of a kubeconfig file
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### Example kubeconfig file
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```yaml
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current-context: federal-context
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apiVersion: v1
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clusters:
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- cluster:
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api-version: v1
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server: http://cow.org:8080
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name: cow-cluster
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- cluster:
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certificate-authority: path/to/my/cafile
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server: https://horse.org:4443
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name: horse-cluster
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- cluster:
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insecure-skip-tls-verify: true
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server: https://pig.org:443
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name: pig-cluster
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contexts:
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- context:
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cluster: horse-cluster
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namespace: chisel-ns
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user: green-user
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name: federal-context
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- context:
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cluster: pig-cluster
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namespace: saw-ns
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user: black-user
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name: queen-anne-context
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kind: Config
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preferences:
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colors: true
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users:
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- name: blue-user
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user:
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token: blue-token
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- name: green-user
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user:
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client-certificate: path/to/my/client/cert
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client-key: path/to/my/client/key
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```
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### Breakdown/explanation of components
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#### cluster
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```yaml
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clusters:
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- cluster:
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certificate-authority: path/to/my/cafile
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server: https://horse.org:4443
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name: horse-cluster
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- cluster:
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insecure-skip-tls-verify: true
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server: https://pig.org:443
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name: pig-cluster
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```
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A `cluster` contains endpoint data for a kubernetes cluster. This includes the fully
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qualified url for the kubernetes apiserver, as well as the cluster's certificate
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authority or `insecure-skip-tls-verify: true`, if the cluster's serving
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certificate is not signed by a system trusted certificate authority.
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A `cluster` has a name (nickname) which acts as a dictionary key for the cluster
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within this kubeconfig file. You can add or modify `cluster` entries using
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[`kubectl config set-cluster`](/docs/user-guide/kubectl/kubectl_config_set-cluster/).
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#### user
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```yaml
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users:
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- name: blue-user
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user:
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token: blue-token
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- name: green-user
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user:
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client-certificate: path/to/my/client/cert
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client-key: path/to/my/client/key
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```
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A `user` defines client credentials for authenticating to a kubernetes cluster. A
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`user` has a name (nickname) which acts as its key within the list of user entries
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after kubeconfig is loaded/merged. Available credentials are `client-certificate`,
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`client-key`, `token`, and `username/password`. `username/password` and `token`
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are mutually exclusive, but client certs and keys can be combined with them.
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You can add or modify `user` entries using
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[`kubectl config set-credentials`](/docs/user-guide/kubectl/kubectl_config_set-credentials).
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#### context
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```yaml
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contexts:
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- context:
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cluster: horse-cluster
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namespace: chisel-ns
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user: green-user
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name: federal-context
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```
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A `context` defines a named [`cluster`](#cluster),[`user`](#user),[`namespace`](/docs/user-guide/namespaces) tuple
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which is used to send requests to the specified cluster using the provided authentication info and
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namespace. Each of the three is optional; it is valid to specify a context with only one of `cluster`,
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`user`,`namespace`, or to specify none. Unspecified values, or named values that don't have corresponding
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entries in the loaded kubeconfig (e.g. if the context specified a `pink-user` for the above kubeconfig file)
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will be replaced with the default. See [Loading and merging rules](#loading-and-merging) below for override/merge behavior.
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You can add or modify `context` entries with [`kubectl config set-context`](/docs/user-guide/kubectl/kubectl_config_set-context).
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#### current-context
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```yaml
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current-context: federal-context
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```
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`current-context` is the nickname or 'key' for the cluster,user,namespace tuple that kubectl
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will use by default when loading config from this file. You can override any of the values in kubectl
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from the commandline, by passing `--context=CONTEXT`, `--cluster=CLUSTER`, `--user=USER`, and/or `--namespace=NAMESPACE` respectively.
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You can change the `current-context` with [`kubectl config use-context`](/docs/user-guide/kubectl/kubectl_config_use-context).
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#### miscellaneous
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```yaml
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apiVersion: v1
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kind: Config
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preferences:
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colors: true
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```
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`apiVersion` and `kind` identify the version and schema for the client parser and should not
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be edited manually.
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`preferences` specify optional (and currently unused) kubectl preferences.
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## Viewing kubeconfig files
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`kubectl config view` will display the current kubeconfig settings. By default
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it will show you all loaded kubeconfig settings; you can filter the view to just
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the settings relevant to the `current-context` by passing `--minify`. See
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[`kubectl config view`](/docs/user-guide/kubectl/kubectl_config_view) for other options.
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## Building your own kubeconfig file
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NOTE, that if you are deploying k8s via kube-up.sh, you do not need to create your own kubeconfig files, the script will do it for you.
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In any case, you can easily use this file as a template to create your own kubeconfig files.
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So, lets do a quick walk through the basics of the above file so you can easily modify it as needed...
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The above file would likely correspond to an api-server which was launched using the `--token-auth-file=tokens.csv` option, where the tokens.csv file looked something like this:
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```conf
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blue-user,blue-user,1
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mister-red,mister-red,2
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```
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Also, since we have other users who validate using **other** mechanisms, the api-server would have probably been launched with other authentication options (there are many such options, make sure you understand which ones YOU care about before crafting a kubeconfig file, as nobody needs to implement all the different permutations of possible authentication schemes).
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- Since the user for the current context is "green-user", any client of the api-server using this kubeconfig file would naturally be able to log in successfully, because we are providing the green-user's client credentials.
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- Similarly, we can operate as the "blue-user" if we choose to change the value of current-context.
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In the above scenario, green-user would have to log in by providing certificates, whereas blue-user would just provide the token. All this information would be handled for us by the
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## Loading and merging rules
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The rules for loading and merging the kubeconfig files are straightforward, but there are a lot of them. The final config is built in this order:
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1. Get the kubeconfig from disk. This is done with the following hierarchy and merge rules:
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If the `CommandLineLocation` (the value of the `kubeconfig` command line option) is set, use this file only. No merging. Only one instance of this flag is allowed.
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Else, if `EnvVarLocation` (the value of `$KUBECONFIG`) is available, use it as a list of files that should be merged.
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Merge files together based on the following rules.
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Empty filenames are ignored. Files with non-deserializable content produced errors.
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The first file to set a particular value or map key wins and the value or map key is never changed.
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This means that the first file to set `CurrentContext` will have its context preserved. It also means that if two files specify a "red-user", only values from the first file's red-user are used. Even non-conflicting entries from the second file's "red-user" are discarded.
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Otherwise, use HomeDirectoryLocation (`~/.kube/config`) with no merging.
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1. Determine the context to use based on the first hit in this chain
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1. command line argument - the value of the `context` command line option
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1. `current-context` from the merged kubeconfig file
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1. Empty is allowed at this stage
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1. Determine the cluster info and user to use. At this point, we may or may not have a context. They are built based on the first hit in this chain. (run it twice, once for user, once for cluster)
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1. command line argument - `user` for user name and `cluster` for cluster name
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1. If context is present, then use the context's value
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1. Empty is allowed
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1. Determine the actual cluster info to use. At this point, we may or may not have a cluster info. Build each piece of the cluster info based on the chain (first hit wins):
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1. command line arguments - `server`, `api-version`, `certificate-authority`, and `insecure-skip-tls-verify`
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1. If cluster info is present and a value for the attribute is present, use it.
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1. If you don't have a server location, error.
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1. Determine the actual user info to use. User is built using the same rules as cluster info, EXCEPT that you can only have one authentication technique per user.
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1. Load precedence is 1) command line flag, 2) user fields from kubeconfig
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1. The command line flags are: `client-certificate`, `client-key`, `username`, `password`, and `token`.
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1. If there are two conflicting techniques, fail.
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1. For any information still missing, use default values and potentially prompt for authentication information
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1. All file references inside of a kubeconfig file are resolved relative to the location of the kubeconfig file itself. When file references are presented on the command line
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they are resolved relative to the current working directory. When paths are saved in the ~/.kube/config, relative paths are stored relatively while absolute paths are stored absolutely.
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Any path in a kubeconfig file is resolved relative to the location of the kubeconfig file itself.
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## Manipulation of kubeconfig via `kubectl config <subcommand>`
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In order to more easily manipulate kubeconfig files, there are a series of subcommands to `kubectl config` to help.
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See [kubectl/kubectl_config.md](/docs/user-guide/kubectl/kubectl_config) for help.
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### Example
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```shell
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$ kubectl config set-credentials myself --username=admin --password=secret
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$ kubectl config set-cluster local-server --server=http://localhost:8080
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$ kubectl config set-context default-context --cluster=local-server --user=myself
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$ kubectl config use-context default-context
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$ kubectl config set contexts.default-context.namespace the-right-prefix
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$ kubectl config view
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```
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produces this output
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```yaml
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apiVersion: v1
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clusters:
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- cluster:
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server: http://localhost:8080
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name: local-server
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contexts:
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- context:
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cluster: local-server
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namespace: the-right-prefix
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user: myself
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name: default-context
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current-context: default-context
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kind: Config
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preferences: {}
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users:
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- name: myself
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user:
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password: secret
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username: admin
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```
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and a kubeconfig file that looks like this
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```yaml
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apiVersion: v1
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clusters:
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- cluster:
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server: http://localhost:8080
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name: local-server
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contexts:
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- context:
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cluster: local-server
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namespace: the-right-prefix
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user: myself
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name: default-context
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current-context: default-context
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kind: Config
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preferences: {}
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users:
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- name: myself
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user:
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password: secret
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username: admin
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```
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#### Commands for the example file
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```shell
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$ kubectl config set preferences.colors true
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$ kubectl config set-cluster cow-cluster --server=http://cow.org:8080 --api-version=v1
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$ kubectl config set-cluster horse-cluster --server=https://horse.org:4443 --certificate-authority=path/to/my/cafile
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$ kubectl config set-cluster pig-cluster --server=https://pig.org:443 --insecure-skip-tls-verify=true
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$ kubectl config set-credentials blue-user --token=blue-token
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$ kubectl config set-credentials green-user --client-certificate=path/to/my/client/cert --client-key=path/to/my/client/key
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$ kubectl config set-context queen-anne-context --cluster=pig-cluster --user=black-user --namespace=saw-ns
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$ kubectl config set-context federal-context --cluster=horse-cluster --user=green-user --namespace=chisel-ns
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$ kubectl config use-context federal-context
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```
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### Final notes for tying it all together
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So, tying this all together, a quick start to creating your own kubeconfig file:
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- Take a good look and understand how your api-server is being launched: You need to know YOUR security requirements and policies before you can design a kubeconfig file for convenient authentication.
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- Replace the snippet above with information for your cluster's api-server endpoint.
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- Make sure your api-server is launched in such a way that at least one user (i.e. green-user) credentials are provided to it. You will of course have to look at api-server documentation in order to determine the current state-of-the-art in terms of providing authentication details.
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