113 lines
4.1 KiB
Markdown
113 lines
4.1 KiB
Markdown
---
|
|
title: Accessing the Kubernetes API from a Pod
|
|
content_type: task
|
|
weight: 120
|
|
---
|
|
|
|
<!-- overview -->
|
|
|
|
This guide demonstrates how to access the Kubernetes API from within a pod.
|
|
|
|
## {{% heading "prerequisites" %}}
|
|
|
|
{{< include "task-tutorial-prereqs.md" >}}
|
|
|
|
<!-- steps -->
|
|
|
|
## Accessing the API from within a Pod
|
|
|
|
When accessing the API from within a Pod, locating and authenticating
|
|
to the API server are slightly different to the external client case.
|
|
|
|
The easiest way to use the Kubernetes API from a Pod is to use
|
|
one of the official [client libraries](/docs/reference/using-api/client-libraries/). These
|
|
libraries can automatically discover the API server and authenticate.
|
|
|
|
### Using Official Client Libraries
|
|
|
|
From within a Pod, the recommended ways to connect to the Kubernetes API are:
|
|
|
|
- For a Go client, use the official [Go client library](https://github.com/kubernetes/client-go/).
|
|
The `rest.InClusterConfig()` function handles API host discovery and authentication automatically.
|
|
See [an example here](https://git.k8s.io/client-go/examples/in-cluster-client-configuration/main.go).
|
|
|
|
- For a Python client, use the official [Python client library](https://github.com/kubernetes-client/python/).
|
|
The `config.load_incluster_config()` function handles API host discovery and authentication automatically.
|
|
See [an example here](https://github.com/kubernetes-client/python/blob/master/examples/in_cluster_config.py).
|
|
|
|
- There are a number of other libraries available, please refer to the [Client Libraries](/docs/reference/using-api/client-libraries/) page.
|
|
|
|
In each case, the service account credentials of the Pod are used to communicate
|
|
securely with the API server.
|
|
|
|
### Directly accessing the REST API
|
|
|
|
While running in a Pod, the Kubernetes apiserver is accessible via a Service named
|
|
`kubernetes` in the `default` namespace. Therefore, Pods can use the
|
|
`kubernetes.default.svc` hostname to query the API server. Official client libraries
|
|
do this automatically.
|
|
|
|
The recommended way to authenticate to the API server is with a
|
|
[service account](/docs/tasks/configure-pod-container/configure-service-account/)
|
|
credential. By default, a Pod
|
|
is associated with a service account, and a credential (token) for that
|
|
service account is placed into the filesystem tree of each container in that Pod,
|
|
at `/var/run/secrets/kubernetes.io/serviceaccount/token`.
|
|
|
|
If available, a certificate bundle is placed into the filesystem tree of each
|
|
container at `/var/run/secrets/kubernetes.io/serviceaccount/ca.crt`, and should be
|
|
used to verify the serving certificate of the API server.
|
|
|
|
Finally, the default namespace to be used for namespaced API operations is placed in a file
|
|
at `/var/run/secrets/kubernetes.io/serviceaccount/namespace` in each container.
|
|
|
|
### Using kubectl proxy
|
|
|
|
If you would like to query the API without an official client library, you can run `kubectl proxy`
|
|
as the [command](/docs/tasks/inject-data-application/define-command-argument-container/)
|
|
of a new sidecar container in the Pod. This way, `kubectl proxy` will authenticate
|
|
to the API and expose it on the `localhost` interface of the Pod, so that other containers
|
|
in the Pod can use it directly.
|
|
|
|
### Without using a proxy
|
|
|
|
It is possible to avoid using the kubectl proxy by passing the authentication token
|
|
directly to the API server. The internal certificate secures the connection.
|
|
|
|
```shell
|
|
# Point to the internal API server hostname
|
|
APISERVER=https://kubernetes.default.svc
|
|
|
|
# Path to ServiceAccount token
|
|
SERVICEACCOUNT=/var/run/secrets/kubernetes.io/serviceaccount
|
|
|
|
# Read this Pod's namespace
|
|
NAMESPACE=$(cat ${SERVICEACCOUNT}/namespace)
|
|
|
|
# Read the ServiceAccount bearer token
|
|
TOKEN=$(cat ${SERVICEACCOUNT}/token)
|
|
|
|
# Reference the internal certificate authority (CA)
|
|
CACERT=${SERVICEACCOUNT}/ca.crt
|
|
|
|
# Explore the API with TOKEN
|
|
curl --cacert ${CACERT} --header "Authorization: Bearer ${TOKEN}" -X GET ${APISERVER}/api
|
|
```
|
|
|
|
The output will be similar to this:
|
|
|
|
```json
|
|
{
|
|
"kind": "APIVersions",
|
|
"versions": [
|
|
"v1"
|
|
],
|
|
"serverAddressByClientCIDRs": [
|
|
{
|
|
"clientCIDR": "0.0.0.0/0",
|
|
"serverAddress": "10.0.1.149:443"
|
|
}
|
|
]
|
|
}
|
|
```
|