Access Services Running on Clusters

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 must be 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 a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

• Killercoda
• Play with Kubernetes

Accessing services running on the cluster

In Kubernetes, nodes, pods and 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 and kubectl 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 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.
• 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 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:

kubectl cluster-info

The output is similar to this:

Kubernetes master is running at https://192.0.2.1
elasticsearch-logging is running at https://192.0.2.1/api/v1/namespaces/kube-system/services/elasticsearch-logging/proxy
kibana-logging is running at https://192.0.2.1/api/v1/namespaces/kube-system/services/kibana-logging/proxy
kube-dns is running at https://192.0.2.1/api/v1/namespaces/kube-system/services/kube-dns/proxy
grafana is running at https://192.0.2.1/api/v1/namespaces/kube-system/services/monitoring-grafana/proxy
heapster is running at https://192.0.2.1/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://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/.

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 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 also use 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 http
• https:<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:kimchy
  

• To 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=true
  

  The 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 a way that is unaware of the proxy path prefix.