262 lines
10 KiB
Markdown
262 lines
10 KiB
Markdown
---
|
|
title: Access Clusters Using the Kubernetes API
|
|
content_template: templates/task
|
|
---
|
|
|
|
{{% capture overview %}}
|
|
This page shows how to access clusters using the Kubernetes API.
|
|
{{% /capture %}}
|
|
|
|
{{% capture prerequisites %}}
|
|
|
|
{{< include "task-tutorial-prereqs.md" >}} {{< version-check >}}
|
|
{{% /capture %}}
|
|
|
|
{{% capture steps %}}
|
|
|
|
## Accessing the cluster API
|
|
|
|
### Accessing for the first time with kubectl
|
|
|
|
When accessing the Kubernetes API for the first time, use the
|
|
Kubernetes command-line tool, `kubectl`.
|
|
|
|
To access a cluster, you need to know the location of the cluster and have credentials
|
|
to access it. Typically, this is automatically set-up when you work through
|
|
a [Getting started guide](/docs/setup/),
|
|
or someone else setup the cluster and provided you with credentials and a location.
|
|
|
|
Check the location and credentials that kubectl knows about with this command:
|
|
|
|
```shell
|
|
kubectl config view
|
|
```
|
|
|
|
Many of the [examples](https://github.com/kubernetes/examples/tree/{{< param "githubbranch" >}}/) provide an introduction to using
|
|
kubectl. Complete documentation is found in the [kubectl manual](/docs/reference/kubectl/overview/).
|
|
|
|
### Directly accessing the REST API
|
|
|
|
kubectl handles locating and authenticating to the API server. If you want to directly access the REST API with an http client like
|
|
`curl` or `wget`, or a browser, there are multiple ways you can locate and authenticate against the API server:
|
|
|
|
1. Run kubectl in proxy mode (recommended). This method is recommended, since it uses the stored apiserver location and verifies the identity of the API server using a self-signed cert. No man-in-the-middle (MITM) attack is possible using this method.
|
|
1. Alternatively, you can provide the location and credentials directly to the http client. This works with client code that is confused by proxies. To protect against man in the middle attacks, you'll need to import a root cert into your browser.
|
|
|
|
Using the Go or Python client libraries provides accessing kubectl in proxy mode.
|
|
|
|
#### Using kubectl proxy
|
|
|
|
The following command runs kubectl in a mode where it acts as a reverse proxy. It handles
|
|
locating the API server and authenticating.
|
|
|
|
Run it like this:
|
|
|
|
```shell
|
|
kubectl proxy --port=8080 &
|
|
```
|
|
|
|
See [kubectl proxy](/docs/reference/generated/kubectl/kubectl-commands/#proxy) for more details.
|
|
|
|
Then you can explore the API with curl, wget, or a browser, like so:
|
|
|
|
```shell
|
|
curl http://localhost:8080/api/
|
|
```
|
|
|
|
The output is similar to this:
|
|
|
|
```json
|
|
{
|
|
"versions": [
|
|
"v1"
|
|
],
|
|
"serverAddressByClientCIDRs": [
|
|
{
|
|
"clientCIDR": "0.0.0.0/0",
|
|
"serverAddress": "10.0.1.149:443"
|
|
}
|
|
]
|
|
}
|
|
```
|
|
|
|
#### Without kubectl proxy
|
|
|
|
It is possible to avoid using kubectl proxy by passing an authentication token
|
|
directly to the API server, like this:
|
|
|
|
Using `grep/cut` approach:
|
|
|
|
```shell
|
|
# Check all possible clusters, as you .KUBECONFIG may have multiple contexts:
|
|
kubectl config view -o jsonpath='{"Cluster name\tServer\n"}{range .clusters[*]}{.name}{"\t"}{.cluster.server}{"\n"}{end}'
|
|
|
|
# Select name of cluster you want to interact with from above output:
|
|
export CLUSTER_NAME="some_server_name"
|
|
|
|
# Point to the API server refering the cluster name
|
|
APISERVER=$(kubectl config view -o jsonpath="{.clusters[?(@.name==\"$CLUSTER_NAME\")].cluster.server}")
|
|
|
|
# Gets the token value
|
|
TOKEN=$(kubectl get secrets -o jsonpath="{.items[?(@.metadata.annotations['kubernetes\.io/service-account\.name']=='default')].data.token}"|base64 -d)
|
|
|
|
# Explore the API with TOKEN
|
|
curl -X GET $APISERVER/api --header "Authorization: Bearer $TOKEN" --insecure
|
|
```
|
|
|
|
The output is similar to this:
|
|
|
|
```json
|
|
{
|
|
"kind": "APIVersions",
|
|
"versions": [
|
|
"v1"
|
|
],
|
|
"serverAddressByClientCIDRs": [
|
|
{
|
|
"clientCIDR": "0.0.0.0/0",
|
|
"serverAddress": "10.0.1.149:443"
|
|
}
|
|
]
|
|
}
|
|
```
|
|
|
|
Using `jsonpath` approach:
|
|
|
|
```shell
|
|
APISERVER=$(kubectl config view --minify -o jsonpath='{.clusters[0].cluster.server}')
|
|
TOKEN=$(kubectl get secret $(kubectl get serviceaccount default -o jsonpath='{.secrets[0].name}') -o jsonpath='{.data.token}' | base64 --decode )
|
|
curl $APISERVER/api --header "Authorization: Bearer $TOKEN" --insecure
|
|
{
|
|
"kind": "APIVersions",
|
|
"versions": [
|
|
"v1"
|
|
],
|
|
"serverAddressByClientCIDRs": [
|
|
{
|
|
"clientCIDR": "0.0.0.0/0",
|
|
"serverAddress": "10.0.1.149:443"
|
|
}
|
|
]
|
|
}
|
|
```
|
|
|
|
The above example uses the `--insecure` flag. This leaves it subject to MITM
|
|
attacks. When kubectl accesses the cluster it uses a stored root certificate
|
|
and client certificates to access the server. (These are installed in the
|
|
`~/.kube` directory). Since cluster certificates are typically self-signed, it
|
|
may take special configuration to get your http client to use root
|
|
certificate.
|
|
|
|
On some clusters, the API server does not require authentication; it may serve
|
|
on localhost, or be protected by a firewall. There is not a standard
|
|
for this. [Configuring Access to the API](/docs/reference/access-authn-authz/controlling-access/)
|
|
describes how a cluster admin can configure this. Such approaches may conflict
|
|
with future high-availability support.
|
|
|
|
### Programmatic access to the API
|
|
|
|
Kubernetes officially supports client libraries for [Go](#go-client) and
|
|
[Python](#python-client).
|
|
|
|
#### Go client
|
|
|
|
* To get the library, run the following command: `go get k8s.io/client-go/<version number>/kubernetes` See [https://github.com/kubernetes/client-go](https://github.com/kubernetes/client-go) to see which versions are supported.
|
|
* Write an application atop of the client-go clients. Note that client-go defines its own API objects, so if needed, please import API definitions from client-go rather than from the main repository, e.g., `import "k8s.io/client-go/1.4/pkg/api/v1"` is correct.
|
|
|
|
The Go client can use the same [kubeconfig file](/docs/concepts/cluster-administration/authenticate-across-clusters-kubeconfig/)
|
|
as the kubectl CLI does to locate and authenticate to the API server. See this [example](https://git.k8s.io/client-go/examples/out-of-cluster-client-configuration/main.go):
|
|
|
|
```golang
|
|
import (
|
|
"fmt"
|
|
"k8s.io/client-go/1.4/kubernetes"
|
|
"k8s.io/client-go/1.4/pkg/api/v1"
|
|
"k8s.io/client-go/1.4/tools/clientcmd"
|
|
)
|
|
...
|
|
// uses the current context in kubeconfig
|
|
config, _ := clientcmd.BuildConfigFromFlags("", "path to kubeconfig")
|
|
// creates the clientset
|
|
clientset, _:= kubernetes.NewForConfig(config)
|
|
// access the API to list pods
|
|
pods, _:= clientset.CoreV1().Pods("").List(v1.ListOptions{})
|
|
fmt.Printf("There are %d pods in the cluster\n", len(pods.Items))
|
|
...
|
|
```
|
|
|
|
If the application is deployed as a Pod in the cluster, please refer to the [next section](#accessing-the-api-from-a-pod).
|
|
|
|
#### Python client
|
|
|
|
To use [Python client](https://github.com/kubernetes-client/python), run the following command: `pip install kubernetes` See [Python Client Library page](https://github.com/kubernetes-client/python) for more installation options.
|
|
|
|
The Python client can use the same [kubeconfig file](/docs/concepts/cluster-administration/authenticate-across-clusters-kubeconfig/)
|
|
as the kubectl CLI does to locate and authenticate to the API server. See this [example](https://github.com/kubernetes-client/python/blob/master/examples/out_of_cluster_config.py):
|
|
|
|
```python
|
|
from kubernetes import client, config
|
|
|
|
config.load_kube_config()
|
|
|
|
v1=client.CoreV1Api()
|
|
print("Listing pods with their IPs:")
|
|
ret = v1.list_pod_for_all_namespaces(watch=False)
|
|
for i in ret.items:
|
|
print("%s\t%s\t%s" % (i.status.pod_ip, i.metadata.namespace, i.metadata.name))
|
|
```
|
|
|
|
#### Other languages
|
|
|
|
There are [client libraries](/docs/reference/using-api/client-libraries/) for accessing the API from other languages. See documentation for other libraries for how they authenticate.
|
|
|
|
### Accessing the API from a Pod
|
|
|
|
When accessing the API from a Pod, locating and authenticating
|
|
to the API server are somewhat different.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
From within a Pod, the recommended way to authenticate to the API server is with a
|
|
[service account](/docs/user-guide/service-accounts) 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.
|
|
|
|
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).
|
|
|
|
- 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.
|
|
|
|
In each case, the service account credentials of the Pod are used to communicate
|
|
securely with the API server.
|
|
|
|
{{% /capture %}}
|
|
|
|
|