website/content/en/docs/tasks/access-application-cluster/access-cluster.md

---
title: Accessing Clusters
weight: 20
content_type: concept
---

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This topic discusses multiple ways to interact with clusters.

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## Accessing for the first time with kubectl

When accessing the Kubernetes API for the first time, we suggest using the
Kubernetes CLI, `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 set up 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](/docs/reference/kubectl/quick-reference/) provide an introduction to using
`kubectl`, and complete documentation is found in the
[kubectl reference](/docs/reference/kubectl/).

## Directly accessing the REST API

Kubectl handles locating and authenticating to the apiserver.
If you want to directly access the REST API with an http client like
curl or wget, or a browser, there are several ways to locate and authenticate:

- Run kubectl in proxy mode.
  - Recommended approach.
  - Uses stored apiserver location.
  - Verifies identity of apiserver using self-signed cert. No MITM possible.
  - Authenticates to apiserver.
  - In future, may do intelligent client-side load-balancing and failover.
- Provide the location and credentials directly to the http client.
  - Alternate approach.
  - Works with some types of client code that are confused by using a proxy.
  - Need to import a root cert into your browser to protect against MITM.

### Using kubectl proxy

The following command runs kubectl in a mode where it acts as a reverse proxy. It handles
locating the apiserver 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, replacing localhost
with [::1] for IPv6, like so:

```shell
curl http://localhost:8080/api/
```

The output is similar to this:

```json
{
  "kind": "APIVersions",
  "versions": [
    "v1"
  ],
  "serverAddressByClientCIDRs": [
    {
      "clientCIDR": "0.0.0.0/0",
      "serverAddress": "10.0.1.149:443"
    }
  ]
}
```

### Without kubectl proxy

Use `kubectl apply` and `kubectl describe secret...` to create a token for the default service account with grep/cut:

First, create the Secret, requesting a token for the default ServiceAccount:

```shell
kubectl apply -f - <<EOF
apiVersion: v1
kind: Secret
metadata:
  name: default-token
  annotations:
    kubernetes.io/service-account.name: default
type: kubernetes.io/service-account-token
EOF
```

Next, wait for the token controller to populate the Secret with a token:

```shell
while ! kubectl describe secret default-token | grep -E '^token' >/dev/null; do
  echo "waiting for token..." >&2
  sleep 1
done
```

Capture and use the generated token:

```shell
APISERVER=$(kubectl config view --minify | grep server | cut -f 2- -d ":" | tr -d " ")
TOKEN=$(kubectl describe secret default-token | grep -E '^token' | cut -f2 -d':' | tr -d " ")

curl $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`:

```shell
APISERVER=$(kubectl config view --minify -o jsonpath='{.clusters[0].cluster.server}')
TOKEN=$(kubectl get secret default-token -o jsonpath='{.data.token}' | base64 --decode)

curl $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"
    }
  ]
}
```

The above examples use 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 apiserver does not require authentication; it may serve
on localhost, or be protected by a firewall. There is not a standard
for this. [Controlling Access to the API](/docs/concepts/security/controlling-access)
describes how a cluster admin can configure this.

## Programmatic access to the API

Kubernetes officially supports [Go](#go-client) and [Python](#python-client)
client libraries.

### Go client

* To get the library, run the following command: `go get k8s.io/client-go@kubernetes-<kubernetes-version-number>`,
  see [INSTALL.md](https://github.com/kubernetes/client-go/blob/master/INSTALL.md#for-the-casual-user)
  for detailed installation instructions. See
  [https://github.com/kubernetes/client-go](https://github.com/kubernetes/client-go#compatibility-matrix)
  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/kubernetes"` is correct.

The Go client can use the same [kubeconfig file](/docs/concepts/configuration/organize-cluster-access-kubeconfig/)
as the kubectl CLI does to locate and authenticate to the apiserver. See this
[example](https://git.k8s.io/client-go/examples/out-of-cluster-client-configuration/main.go).

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/configuration/organize-cluster-access-kubeconfig/)
as the kubectl CLI does to locate and authenticate to the apiserver. See this
[example](https://github.com/kubernetes-client/python/tree/master/examples).

### 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.

Please check [Accessing the API from within a Pod](/docs/tasks/run-application/access-api-from-pod/)
for more details.

## Accessing services running on the cluster

The previous section describes how to connect to the Kubernetes API server.
For information about connecting to other services running on a Kubernetes cluster, see
[Access Cluster Services](/docs/tasks/access-application-cluster/access-cluster-services/).

## Requesting redirects

The redirect capabilities have been deprecated and removed. Please use a proxy (see below) instead.

## So many proxies

There are several different proxies you may encounter when using Kubernetes:

1. The [kubectl proxy](#directly-accessing-the-rest-api):

   - runs on a user's desktop or in a pod
   - proxies from a localhost address to the Kubernetes apiserver
   - client to proxy uses HTTP
   - proxy to apiserver uses HTTPS
   - locates apiserver
   - adds authentication headers

1. The [apiserver proxy](/docs/tasks/access-application-cluster/access-cluster-services/#discovering-builtin-services):

   - is a bastion built into the apiserver
   - connects a user outside of the cluster to cluster IPs which otherwise might not be reachable
   - runs in the apiserver processes
   - client to proxy uses HTTPS (or http if apiserver so configured)
   - proxy to target may use HTTP or HTTPS as chosen by proxy using available information
   - can be used to reach a Node, Pod, or Service
   - does load balancing when used to reach a Service

1. The [kube proxy](/docs/concepts/services-networking/service/#ips-and-vips):

   - runs on each node
   - proxies UDP and TCP
   - does not understand HTTP
   - provides load balancing
   - is only used to reach services

1. A Proxy/Load-balancer in front of apiserver(s):

   - existence and implementation varies from cluster to cluster (e.g. nginx)
   - sits between all clients and one or more apiservers
   - acts as load balancer if there are several apiservers.

1. Cloud Load Balancers on external services:

   - are provided by some cloud providers (e.g. AWS ELB, Google Cloud Load Balancer)
   - are created automatically when the Kubernetes service has type `LoadBalancer`
   - use UDP/TCP only
   - implementation varies by cloud provider.

Kubernetes users will typically not need to worry about anything other than the first two types. The cluster admin
will typically ensure that the latter types are set up correctly.