Connecting Clients

Accessing the Kubernetes API with and without TLS verification, and managing multiple clusters

Prerequisites

  • Before attempting to connect to the Kubernetes cluster, ensure that you have correctly exposed the Kubernetes API to outside the DC/OS cluster. This can be achieved, for example, by following the steps described in Exposing the Kubernetes API.

  • Also ensure that kubectl is installed and available in the terminal session. If you installed the Kubernetes package through the DC/OS UI, you will also need to install the dcos kubernetes CLI:

    dcos package install kubernetes --cli
    
  • Ensure that dcos is adequately configured to access the desired DC/OS cluster before proceeding.

WARNING: dcos MUST be configured to access the desired DC/OS cluster over HTTPS before proceeding.
The following command must return a URL that starts with https://
$ dcos config show core.dcos_url

In case the returned URL doesn't start with https:// run:
$ dcos config set core.dcos_url https://<master-ip> Also if the TLS certificate used by DC/OS is not trusted you additionally need to run the following command to disable TLS verification:
<$ dcos config set core.ssl_verify false

Without TLS verification

In order to configure kubectl to access the Kubernetes API without validating the presented TLS certificate, run the following command, replacing https://kube-apiserver.example.com:6443 with the URL at which the Kubernetes API is exposed to outside the DC/OS cluster:

dcos kubernetes cluster kubeconfig \
    --cluster-name=CLUSTER-NAME \
    --apiserver-url https://kube-apiserver.example.com:6443 \
    --insecure-skip-tls-verify

With TLS verification

In order to configure kubectl to access the Kubernetes API while validating the presented TLS certificate run the dcos kubernetes cluster kubeconfig command. Use ca.crt for the path to the CA certificate that signed the certificate used to expose the Kubernetes API. Replace https://kube-apiserver.example.com:6443 with the URL at which the Kubernetes API is exposed to outside the DC/OS cluster.

dcos kubernetes cluster kubeconfig \
    --cluster-name=CLUSTER-NAME \
    --apiserver-url https://kube-apiserver.example.com:6443 \
    --path-to-custom-ca ca.pem

From this point on, any kubectl calls should simply work, depending on the Kubernetes API authorization mode configured and the permissions given to the user’s Kubernetes service account.

Managing multiple clusters

To interact with multiple Kubernetes clusters, kubectl supports contexts, a group of access parameters that defines how to connect to a cluster.

To create the DC/OS Kubernetes config without switching the context, run:

$ dcos kubernetes cluster kubeconfig \
    --cluster-name=CLUSTER-NAME \
    --apiserver-url https://kube-apiserver.example.com:6443 \
    --path-to-custom-ca ca.pem \
    --no-activate-context
kubeconfig context 'kube-apiserver-example-com6443' created successfully

To switch to the DC/OS Kubernetes cluster context, run:

$ kubectl config use-context kube-apiserver-example-com6443
Switched to context "kube-apiserver-example-com6443".

Or specify the context when running commands:

$ kubectl get nodes --context=kube-apiserver-example-com6443
NAME                                             STATUS    ROLES     AGE       VERSION
kube-control-plane-0-instance.kubernetes-cluster.mesos   Ready     master    44m       v1.12.5
kube-node-0-kubelet.kubernetes-cluster.mesos             Ready     <none>    43m       v1.12.5

By default, the kubeconfig context name is derived from the value of the --apiserver-url flag. To make the context name easier to remember and switch between, you can specify a name by using the --context-name flag:

$ dcos kubernetes cluster kubeconfig \
    --cluster-name=CLUSTER-NAME \
    --apiserver-url https://kube-apiserver.example.com:6443 \
    --path-to-custom-ca ca.pem \
    --context-name=my-context

NOTE: dcos kubernetes cluster kubeconfig --cluster-name=CLUSTER-NAME will refuse to overwrite existing user, context and cluster entries whose name matches the value of the --context-name flag (or the value derived from the value of the --apiserver-url flag) in case --context-name is not specified. As such, make sure to provide a unique, non-existing value for --context-name.