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cn/docs/tasks/access-application-cluster/access-cluster.md
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---
title: Accessing Clusters
---
* TOC
{:toc}
## Accessing the cluster API
### 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/getting-started-guides/),
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/kubernetes/tree/{{page.githubbranch}}/examples/) provide an introduction to using
kubectl and complete documentation is found in the [kubectl manual](/docs/user-guide/kubectl/index).
### 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/user-guide/kubectl/v1.6/#proxy) for more details.
Then you can explore the API with curl, wget, or a browser, like so:
```shell
$ curl http://localhost:8080/api/
{
"versions": [
"v1"
]
}
```
#### Without kubectl proxy (before v1.3.x)
It is possible to avoid using kubectl proxy by passing an authentication token
directly to the apiserver, like this:
```shell
$ APISERVER=$(kubectl config view | grep server | cut -f 2- -d ":" | tr -d " ")
$ TOKEN=$(kubectl config view | grep token | cut -f 2 -d ":" | tr -d " ")
$ curl $APISERVER/api --header "Authorization: Bearer $TOKEN" --insecure
{
"versions": [
"v1"
]
}
```
#### Without kubectl proxy (post v1.3.x)
In Kubernetes version 1.3 or later, `kubectl config view` no longer displays the token. Use `kubectl describe secret...` to get the token for the default service account, like this:
``` shell
$ APISERVER=$(kubectl config view | grep server | cut -f 2- -d ":" | tr -d " ")
$ TOKEN=$(kubectl describe secret $(kubectl get secrets | grep default | cut -f1 -d ' ') | grep -E '^token' | cut -f2 -d':' | tr -d '\t')
$ 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 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. [Configuring Access to the API](/docs/admin/accessing-the-api)
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 [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/<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 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-incubator/client-python), run the following command: `pip install kubernetes`. See [Python Client Library page](https://github.com/kubernetes-incubator/client-python) for more installation options.
The Python client can use the same [kubeconfig file](/docs/user-guide/kubeconfig-file)
as the kubectl CLI does to locate and authenticate to the apiserver. See this [example](https://github.com/kubernetes-incubator/client-python/tree/master/examples/example1.py).
#### Other languages
There are [client libraries](/docs/reference/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 apiserver are somewhat different.
The recommended way to locate the apiserver within the pod is with
the `kubernetes` DNS name, which resolves to a Service IP which in turn
will be routed to an apiserver.
The recommended way to authenticate to the apiserver is with a
[service account](/docs/tasks/configure-pod-container/configure-service-account/) credential. By kube-system, 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 apiserver.
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 API are:
- run a kubectl proxy as one of the containers in the pod, or as a background
process within a container. This proxies the
Kubernetes API to the localhost interface of the pod, so that other processes
in any container of the pod can access it. See this [example of using kubectl proxy
in a pod](https://github.com/kubernetes/kubernetes/tree/{{page.githubbranch}}/examples/kubectl-container/).
- use the Go client library, and create a client using the `rest.InClusterConfig()` and `kubernetes.NewForConfig()` functions.
They handle locating and authenticating to the apiserver. [example](https://git.k8s.io/client-go/examples/in-cluster-client-configuration/main.go)
In each case, the credentials of the pod are used to communicate securely with the apiserver.
## Accessing services running on the cluster
The previous section was about connecting the Kubernetes API server. This section is about
connecting to other services running on Kubernetes cluster. In Kubernetes, the
[nodes](/docs/admin/node), [pods](/docs/user-guide/pods) and [services](/docs/user-guide/services) all have
their own IPs. In many cases, the node IPs, pod IPs, and some service IPs on a cluster will not be
routable, so they will not be reachable from a machine outside the cluster,
such as your desktop machine.
### Ways to connect
You have several options for connecting to nodes, pods and services from outside the cluster:
- Access services through public IPs.
- Use a service with type `NodePort` or `LoadBalancer` to make the service reachable outside
the cluster. See the [services](/docs/user-guide/services) and
[kubectl expose](/docs/user-guide/kubectl/v1.6/#expose) documentation.
- Depending on your cluster environment, this may just expose the service to your corporate network,
or it may expose it to the internet. Think about whether the service being exposed is secure.
Does it do its own authentication?
- Place pods behind services. To access one specific pod from a set of replicas, such as for debugging,
place a unique label on the pod and create a new service which selects this label.
- In most cases, it should not be necessary for application developer to directly access
nodes via their nodeIPs.
- Access services, nodes, or pods using the Proxy Verb.
- Does apiserver authentication and authorization prior to accessing the remote service.
Use this if the services are not secure enough to expose to the internet, or to gain
access to ports on the node IP, or for debugging.
- Proxies may cause problems for some web applications.
- Only works for HTTP/HTTPS.
- Described [here](#manually-constructing-apiserver-proxy-urls).
- Access from a node or pod in the cluster.
- Run a pod, and then connect to a shell in it using [kubectl exec](/docs/user-guide/kubectl/v1.6/#exec).
Connect to other nodes, pods, and services from that shell.
- Some clusters may allow you to ssh to a node in the cluster. From there you may be able to
access cluster services. This is a non-standard method, and will work on some clusters but
not others. Browsers and other tools may or may not be installed. Cluster DNS may not work.
### Discovering builtin services
Typically, there are several services which are started on a cluster by kube-system. Get a list of these
with the `kubectl cluster-info` command:
```shell
$ kubectl cluster-info
Kubernetes master is running at https://104.197.5.247
elasticsearch-logging is running at https://104.197.5.247/api/v1/namespaces/kube-system/services/elasticsearch-logging/proxy
kibana-logging is running at https://104.197.5.247/api/v1/namespaces/kube-system/services/kibana-logging/proxy
kube-dns is running at https://104.197.5.247/api/v1/namespaces/kube-system/services/kube-dns/proxy
grafana is running at https://104.197.5.247/api/v1/namespaces/kube-system/services/monitoring-grafana/proxy
heapster is running at https://104.197.5.247/api/v1/namespaces/kube-system/services/monitoring-heapster/proxy
```
This shows the proxy-verb URL for accessing each service.
For example, this cluster has cluster-level logging enabled (using Elasticsearch), which can be reached
at `https://104.197.5.247/api/v1/namespaces/kube-system/services/elasticsearch-logging/proxy/` if suitable credentials are passed. Logging can also be reached through a kubectl proxy, for example at:
`http://localhost:8080/api/v1/namespaces/kube-system/services/elasticsearch-logging/proxy/`.
(See [above](#accessing-the-cluster-api) for how to pass credentials or use kubectl proxy.)
#### Manually constructing apiserver proxy URLs
As mentioned above, you use the `kubectl cluster-info` command to retrieve the service's proxy URL. To create proxy URLs that include service endpoints, suffixes, and parameters, you simply append to the service's proxy URL:
`http://`*`kubernetes_master_address`*`/api/v1/namespaces/`*`namespace_name`*`/services/`*`service_name[:port_name]`*`/proxy`
If you haven't specified a name for your port, you don't have to specify *port_name* in the URL.
##### Examples
* To access the Elasticsearch service endpoint `_search?q=user:kimchy`, you would use: `http://104.197.5.247/api/v1/namespaces/kube-system/services/elasticsearch-logging/proxy/_search?q=user:kimchy`
* To access the Elasticsearch cluster health information `_cluster/health?pretty=true`, you would use: `https://104.197.5.247/api/v1/namespaces/kube-system/services/elasticsearch-logging/proxy/_cluster/health?pretty=true`
```json
{
"cluster_name" : "kubernetes_logging",
"status" : "yellow",
"timed_out" : false,
"number_of_nodes" : 1,
"number_of_data_nodes" : 1,
"active_primary_shards" : 5,
"active_shards" : 5,
"relocating_shards" : 0,
"initializing_shards" : 0,
"unassigned_shards" : 5
}
```
#### Using web browsers to access services running on the cluster
You may be able to put an apiserver proxy url into the address bar of a browser. However:
- Web browsers cannot usually pass tokens, so you may need to use basic (password) auth. Apiserver can be configured to accept basic auth,
but your cluster may not be configured to accept basic auth.
- Some web apps may not work, particularly those with client side javascript that construct urls in a
way that is unaware of the proxy path prefix.
## 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](#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/user-guide/services/#ips-and-vips):
- runs on each node
- proxies UDP and TCP
- does not understand HTTP
- provides load balancing
- is just 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 setup correctly.
cn/docs/tasks/access-application-cluster/frontend.yaml
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kind: Service
apiVersion: v1
metadata:
name: frontend
spec:
selector:
app: hello
tier: frontend
ports:
- protocol: "TCP"
port: 80
targetPort: 80
type: LoadBalancer
---
apiVersion: apps/v1beta1
kind: Deployment
metadata:
name: frontend
spec:
replicas: 1
template:
metadata:
labels:
app: hello
tier: frontend
track: stable
spec:
containers:
- name: nginx
image: "gcr.io/google-samples/hello-frontend:1.0"
lifecycle:
preStop:
exec:
command: ["/usr/sbin/nginx","-s","quit"]
cn/docs/tasks/access-application-cluster/hello-service.yaml
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kind: Service
apiVersion: v1
metadata:
name: hello
spec:
selector:
app: hello
tier: backend
ports:
- protocol: TCP
port: 80
targetPort: http
cn/docs/tasks/access-application-cluster/hello.yaml
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apiVersion: apps/v1beta1
kind: Deployment
metadata:
name: hello
spec:
replicas: 7
template:
metadata:
labels:
app: hello
tier: backend
track: stable
spec:
containers:
- name: hello
image: "gcr.io/google-samples/hello-go-gke:1.0"
ports:
- name: http
containerPort: 80
cn/docs/tasks/access-application-cluster/port-forward-access-application-cluster.md
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---
title: Use Port Forwarding to Access Applications in a Cluster
---
{% capture overview %}
This page shows how to use `kubectl port-forward` to connect to a Redis
server running in a Kubernetes cluster. This type of connection can be useful
for database debugging.
{% endcapture %}
{% capture prerequisites %}
* {% include task-tutorial-prereqs.md %}
* Install [redis-cli](http://redis.io/topics/rediscli).
{% endcapture %}
{% capture steps %}
## Creating a pod to run a Redis server
1. Create a pod:
kubectl create -f https://k8s.io/docs/tasks/access-application-cluster/redis-master.yaml
The output of a successful command verifies that the pod was created:
pod "redis-master" created
1. Check to see whether the pod is running and ready:
kubectl get pods
When the pod is ready, the output displays a STATUS of Running:
NAME READY STATUS RESTARTS AGE
redis-master 2/2 Running 0 41s
1. Verify that the Redis server is running in the pod and listening on port 6379:
{% raw %}
kubectl get pods redis-master --template='{{(index (index .spec.containers 0).ports 0).containerPort}}{{"\n"}}'
{% endraw %}
The output displays the port:
6379
## Forward a local port to a port on the pod
1. Forward port 6379 on the local workstation to port 6379 of redis-master pod:
kubectl port-forward redis-master 6379:6379
The output is similar to this:
I0710 14:43:38.274550 3655 portforward.go:225] Forwarding from 127.0.0.1:6379 -> 6379
I0710 14:43:38.274797 3655 portforward.go:225] Forwarding from [::1]:6379 -> 6379
1. Start the Redis command line interface:
redis-cli
1. At the Redis command line prompt, enter the `ping` command:
127.0.0.1:6379>ping
A successful ping request returns PONG.
{% endcapture %}
{% capture discussion %}
## Discussion
Connections made to local port 6379 are forwarded to port 6379 of the pod that
is running the Redis server. With this connection in place you can use your
local workstation to debug the database that is running in the pod.
{% endcapture %}
{% capture whatsnext %}
Learn more about [kubectl port-forward](/docs/user-guide/kubectl/v1.6/#port-forward).
{% endcapture %}
{% include templates/task.md %}
cn/docs/tasks/access-application-cluster/redis-master.yaml
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apiVersion: v1
kind: Pod
metadata:
labels:
name: redis
redis-sentinel: "true"
role: master
name: redis-master
spec:
containers:
- name: master
image: gcr.io/google_containers/redis:v1
env:
- name: MASTER
value: "true"
ports:
- containerPort: 6379
resources:
limits:
cpu: "0.1"
volumeMounts:
- mountPath: /redis-master-data
name: data
- name: sentinel
image: kubernetes/redis:v1
env:
- name: SENTINEL
value: "true"
ports:
- containerPort: 26379
volumes:
- name: data
emptyDir: {}
cn/docs/tasks/access-application-cluster/service-access-application-cluster.md
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---
title: Use a Service to Access an Application in a Cluster
---
{% capture overview %}
This page shows how to create a Kubernetes Service object that external
clients can use to access an application running in a cluster. The Service
provides load balancing for an application that has two running instances.
{% endcapture %}
{% capture prerequisites %}
{% include task-tutorial-prereqs.md %}
{% endcapture %}
{% capture objectives %}
* Run two instances of a Hello World application.
* Create a Service object that exposes a node port.
* Use the Service object to access the running application.
{% endcapture %}
{% capture lessoncontent %}
## Creating a service for an application running in two pods
1. Run a Hello World application in your cluster:
kubectl run hello-world --replicas=2 --labels="run=load-balancer-example" --image=gcr.io/google-samples/node-hello:1.0 --port=8080
The preceding command creates a
[Deployment](/docs/concepts/workloads/controllers/deployment/)
object and an associated
[ReplicaSet](/docs/concepts/workloads/controllers/replicaset/)
object. The ReplicaSet has two
[Pods](/docs/concepts/workloads/pods/pod/),
each of which runs the Hello World application.
1. Display information about the Deployment:
kubectl get deployments hello-world
kubectl describe deployments hello-world
1. Display information about your ReplicaSet objects:
kubectl get replicasets
kubectl describe replicasets
1. Create a Service object that exposes the deployment:
kubectl expose deployment hello-world --type=NodePort --name=example-service
1. Display information about the Service:
kubectl describe services example-service
The output is similar to this:
Name: example-service
Namespace: default
Labels: run=load-balancer-example
Selector: run=load-balancer-example
Type: NodePort
IP: 10.32.0.16
Port: <unset> 8080/TCP
NodePort: <unset> 31496/TCP
Endpoints: 10.200.1.4:8080,10.200.2.5:8080
Session Affinity: None
No events.
Make a note of the NodePort value for the service. For example,
in the preceding output, the NodePort value is 31496.
1. List the pods that are running the Hello World application:
kubectl get pods --selector="run=load-balancer-example" --output=wide
The output is similar to this:
NAME READY STATUS ... IP NODE
hello-world-2895499144-bsbk5 1/1 Running ... 10.200.1.4 worker1
hello-world-2895499144-m1pwt 1/1 Running ... 10.200.2.5 worker2
1. Get the public IP address of one of your nodes that is running
a Hello World pod. How you get this address depends on how you set
up your cluster. For example, if you are using Minikube, you can
see the node address by running `kubectl cluster-info`. If you are
using Google Compute Engine instances, you can use the
`gcloud compute instances list` command to see the public addresses of your
nodes. For more information about this command, see the [GCE documentation](https://cloud.google.com/sdk/gcloud/reference/compute/instances/list).
1. On your chosen node, create a firewall rule that allows TCP traffic
on your node port. For example, if your Service has a NodePort value of
31568, create a firewall rule that allows TCP traffic on port 31568. Different
cloud providers offer different ways of configuring firewall rules. See [the
GCE documentation on firewall rules](https://cloud.google.com/compute/docs/vpc/firewalls),
for example.
1. Use the node address and node port to access the Hello World application:
curl http://<public-node-ip>:<node-port>
where `<public-node-ip>` is the public IP address of your node,
and `<node-port>` is the NodePort value for your service.
The response to a successful request is a hello message:
Hello Kubernetes!
## Using a service configuration file
As an alternative to using `kubectl expose`, you can use a
[service configuration file](/docs/user-guide/services/operations)
to create a Service.
{% endcapture %}
{% capture cleanup %}
To delete the Service, enter this command:
kubectl delete services example-service
To delete the Deployment, the ReplicaSet, and the Pods that are running
the Hello World application, enter this command:
kubectl delete deployment hello-world
{% endcapture %}
{% capture whatsnext %}
Learn more about
[connecting applications with services](/docs/concepts/services-networking/connect-applications-service/).
{% endcapture %}
{% include templates/tutorial.md %}
cn/docs/tasks/access-application-cluster/two-container-pod.yaml
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apiVersion: v1
kind: Pod
metadata:
name: two-containers
spec:
restartPolicy: Never
volumes:
- name: shared-data
emptyDir: {}
containers:
- name: nginx-container
image: nginx
volumeMounts:
- name: shared-data
mountPath: /usr/share/nginx/html
- name: debian-container
image: debian
volumeMounts:
- name: shared-data
mountPath: /pod-data
command: ["/bin/sh"]
args: ["-c", "echo Hello from the debian container > /pod-data/index.html"]