This page shows how to connect to services running on the Kubernetes cluster.
Before you begin
You need to have a Kubernetes cluster, and the kubectl command-line tool mustbe configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have acluster, you can create one by usingminikubeor you can use one of these Kubernetes playgrounds:
To check the version, enter kubectl version.
Accessing services running on the cluster
In Kubernetes, nodes,pods and services all havetheir own IPs. In many cases, the node IPs, pod IPs, and some service IPs on a cluster will not beroutable, 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
NodePortorLoadBalancerto make the service reachable outsidethe cluster. See the services andkubectl expose documentation. - Depending on your cluster environment, this may only 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 accessnodes via their nodeIPs.
- Use a service with type
- 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 gainaccess to ports on the node IP, or for debugging.
- Proxies may cause problems for some web applications.
- Only works for HTTP/HTTPS.
- Described here.
- Access from a node or pod in the cluster.
- Run a pod, and then connect to a shell in it using kubectl 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 toaccess cluster services. This is a non-standard method, and will work on some clusters butnot 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 thesewith the kubectl cluster-info command:
kubectl cluster-infoThe output is similar to this:
Kubernetes master is running at https://192.0.2.1elasticsearch-logging is running at https://192.0.2.1/api/v1/namespaces/kube-system/services/elasticsearch-logging/proxykibana-logging is running at https://192.0.2.1/api/v1/namespaces/kube-system/services/kibana-logging/proxykube-dns is running at https://192.0.2.1/api/v1/namespaces/kube-system/services/kube-dns/proxygrafana is running at https://192.0.2.1/api/v1/namespaces/kube-system/services/monitoring-grafana/proxyheapster is running at https://192.0.2.1/api/v1/namespaces/kube-system/services/monitoring-heapster/proxyThis shows the proxy-verb URL for accessing each service.For example, this cluster has cluster-level logging enabled (using Elasticsearch), which can be reachedat https://192.0.2.1/api/v1/namespaces/kube-system/services/elasticsearch-logging/proxy/if suitable credentials are passed, or through a kubectl proxy at, for example:http://localhost:8080/api/v1/namespaces/kube-system/services/elasticsearch-logging/proxy/.
Note: See Access Clusters Using the Kubernetes APIfor 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 createproxy URLs that include service endpoints, suffixes, and parameters, you append to the service's proxy URL:http://kubernetes_master_address/api/v1/namespaces/namespace_name/services/[https:]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. You can alsouse the port number in place of the port_name for both named and unnamed ports.
By default, the API server proxies to your service using HTTP. To use HTTPS, prefix the service name with https::http://<kubernetes_master_address>/api/v1/namespaces/<namespace_name>/services/<service_name>/proxy
The supported formats for the <service_name> segment of the URL are:
<service_name>- proxies to the default or unnamed port using http<service_name>:<port_name>- proxies to the specified port name or port number using httphttps:<service_name>:- proxies to the default or unnamed port using https (note the trailing colon)https:<service_name>:<port_name>- proxies to the specified port name or port number using https
Examples
To access the Elasticsearch service endpoint
_search?q=user:kimchy, you would use:http://192.0.2.1/api/v1/namespaces/kube-system/services/elasticsearch-logging/proxy/_search?q=user:kimchyTo access the Elasticsearch cluster health information
_cluster/health?pretty=true, you would use:https://192.0.2.1/api/v1/namespaces/kube-system/services/elasticsearch-logging/proxy/_cluster/health?pretty=trueThe health information is similar to this:
{ "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}To access the https Elasticsearch service health information
_cluster/health?pretty=true, you would use:https://192.0.2.1/api/v1/namespaces/kube-system/services/https:elasticsearch-logging:/proxy/_cluster/health?pretty=true
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 away that is unaware of the proxy path prefix.
