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Guided Exercise: The Kubernetes and OpenShift Command-Line Interfaces

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Syarif
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Access an OpenShift cluster using the command-line to get information about cluster services and nodes.

Outcomes

  • Use the OpenShift web console to locate the installation file for the oc OpenShift command-line interface.

  • Get and use a token from the web console to access the cluster from the command line.

  • Identify key differences between the kubectl and oc command-line tools.

  • Identify the main components of OpenShift and Kubernetes.

As the student user on the workstation machine, use the lab command to prepare your system for this exercise.

This command ensures that all resources are available for this exercise.

[student@workstation ~]$ lab start cli-interfaces

Procedure 2.1. Instructions

  1. Log in to the OpenShift web console as the developer user. Locate the installation file for the oc OpenShift command-line interface (CLI).

    1. Open a web browser and then navigate to https://console-openshift-console.apps.ocp4.example.com.

    2. Click Red Hat Identity Management and log in as the developer user with the developer password.

    3. Locate the installation file for the oc CLI. From the OpenShift web console, select Help → Command line tools. The Help menu is represented by a ? icon.

      The oc binary is available for multiple operating systems and architectures. For each operating system and architecture, the oc binary also includes the kubectl binary.

      NOTE

      You do not need to download or install the oc and kubectl binaries, which are already installed on the workstation machine.

  2. Download an authorization token from the web console. Then, use the token and the oc command to log in to the OpenShift cluster.

    1. From the Command Line Tools page, click the Copy login command link.

    2. The link opens a login page. Click Red Hat Identity Management and log in as the developer user with the developer password.

    3. A web page is displayed. Click the Display token link to show your API token and the login command.

    4. Copy the oc login command to your clipboard. Open a terminal window and then use the copied command to log in to the cluster with your token.

       [student@workstation ~]$ oc login --token=sha256-fypX...Ot6A \
   --server=https://api.ocp4.example.com:6443
 Logged into "https://api.ocp4.example.com:6443" as "developer" using the token provided.
 ...output omitted...

  3. Compare the available commands for the kubectl and oc commands.

    1. Use the help command to list and review the available commands for the kubectl command.

       [student@workstation ~]$ kubectl help
 kubectl controls the Kubernetes cluster manager.

  Find more information at: https://kubernetes.io/docs/reference/kubectl/

 Basic Commands (Beginner):
   create          Create a resource from a file or from stdin
   expose          Take a replication controller, service, deployment or pod and expose it as a new Kubernetes service
   run             Run a particular image on the cluster
   set             Set specific features on objects

 Basic Commands (Intermediate):
   explain         Get documentation for a resource
   get             Display one or many resources
   edit            Edit a resource on the server
   delete          Delete resources by file names, stdin, resources and names, or by resources and label selector
 ...output omitted....

      Notice that the kubectl command does not provide a login command.

    2. Examine the available subcommands and options for the kubectl create command by using the --help option.

       [student@workstation ~]$ kubectl create --help
 Create a resource from a file or from stdin.

  JSON and YAML formats are accepted.

 Examples:
   # Create a pod using the data in pod.json
   kubectl create -f ./pod.json
 ...output omitted....
 Available Commands:
   clusterrole           Create a cluster role
   clusterrolebinding    Create a cluster role binding for a particular cluster role
   configmap             Create a config map from a local file, directory or literal value
   cronjob               Create a cron job with the specified name
   deployment            Create a deployment with the specified name
 ...output omitted...
 Options:
     --allow-missing-template-keys=true:
     If true, ignore any errors in templates when a field or map key is missing in the template. Only applies to
     golang and jsonpath output formats.

     --dry-run='none':
     Must be "none", "server", or "client". If client strategy, only print the object that would be sent, without
     sending it. If server strategy, submit server-side request without persisting the resource.
 ...output omitted....
 Usage:
   kubectl create -f FILENAME [options]

 Use "kubectl <command> --help" for more information about a given command.
 Use "kubectl options" for a list of global command-line options (applies to all commands).

      You can use the --help option with any kubectl command. The --help option provides information about a command, including the available subcommands and options, and the command syntax.

    3. List and review the available commands for the oc binary by using the help command.

       [student@workstation ~]$ oc help
 OpenShift Client

 This client helps you develop, build, deploy, and run your applications on any
 OpenShift or Kubernetes cluster. It also includes the administrative
 commands for managing a cluster under the 'adm' subcommand.

 Basic Commands:
   login             Log in to a server
   new-project       Request a new project
   new-app           Create a new application
   status            Show an overview of the current project
   project           Switch to another project
   projects          Display existing projects
   explain           Get documentation for a resource
 ...output omitted....

      The oc command supports the same capabilities as the kubectl command. The oc command provides additional commands to natively support an OpenShift cluster. For example, the new-project command creates a project, which is a Kubernetes namespace, in the OpenShift cluster. The new-app command is unique to the oc command. It creates applications by using existing source code or prebuilt images.

    4. Use the --help option with the oc create command to view the available subcommands and options.

       [student@workstation ~]$ oc create --help
 Create a resource from a file or from stdin.

  JSON and YAML formats are accepted.

 Examples:
   # Create a pod using the data in pod.json
   oc create -f ./pod.json
 ...output omitted...

 Available Commands:
   build                  Create a new build
   clusterresourcequota   Create a cluster resource quota
   clusterrole            Create a cluster role
   clusterrolebinding     Create a cluster role binding for a particular cluster role
   configmap              Create a config map from a local file, directory or literal value
   cronjob                Create a cron job with the specified name
   deployment             Create a deployment with the specified name
   deploymentconfig       Create a deployment config with default options that uses a given image
 ...output omitted....
 Options:
     --allow-missing-template-keys=true:
     If true, ignore any errors in templates when a field or map key is missing in the template. Only applies to
     golang and jsonpath output formats.

     --dry-run='none':
     Must be "none", "server", or "client". If client strategy, only print the object that would be sent, without
     sending it. If server strategy, submit server-side request without persisting the resource.
 ...output omitted...
 Usage:
   oc create -f FILENAME [options]
 ....output omitted....

      The oc create command includes the same subcommands and options as the kubectl create command, and provides additional subcommands for OpenShift resources. For example, you can use the oc create command to create OpenShift resources such as a deployment configuration, a route, and an image stream.

  4. Identify the components and Kubernetes resources of an OpenShift cluster by using the terminal. Unless otherwise noted, all commands are available for the oc and kubectl commands.

    1. In a terminal, use the oc login command to log in to the cluster as the admin user with the redhatocp password. Regular cluster users, such as the developer user, cannot list resources at a cluster scope.

       [student@workstation ~]$ oc login -u admin -p redhatocp
 Login successful
 ...output omitted...

    2. Identify the cluster version with the version command.

       [student@workstation ~]$ oc version
 Client Version: 4.12.0
 Kustomize Version: v4.5.7
 Server Version: 4.12.0
 Kubernetes Version: v1.25.4+77bec7a

    3. Use the cluster-info command to identify the URL for the Kubernetes control plane.

       [student@workstation ~]$ oc cluster-info
 Kubernetes control plane is running at https://api.ocp4.example.com:6443

 To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.

    4. Identify the supported API versions by using the api-versions command.

       [student@workstation ~]$ oc api-versions
 admissionregistration.k8s.io/v1
 apiextensions.k8s.io/v1
 apiregistration.k8s.io/v1
 apiserver.openshift.io/v1
 apps.openshift.io/v1
 apps/v1
 ...output omitted....

    5. List cluster operators with the get clusteroperator command.

       [student@workstation ~]$ oc get clusteroperator
 NAME                        VERSION   AVAILABLE   PROGRESSING   DEGRADED   SINCE ...
 authentication              4.12.0    True        False         False      18d
 baremetal                   4.12.0    True        False         False      18d
 cloud-controller-manager    4.12.0    True        False         False      18d
 cloud-credential            4.12.0    True        False         False      18d
 cluster-autoscaler          4.12.0    True        False         False      18d
 config-operator             4.12.0    True        False         False      18d
 console                     4.12.0    True        False         False      18d
 control-plane-machine-set   4.12.0    True        False         False      18d
 csi-snapshot-controller     4.12.0    True        False         False      18d
 dns                         4.12.0    True        False         False      5h24m
 etcd                        4.12.0    True        False         False      18d
 image-registry              4.12.0    True        False         False      18d
 ingress                     4.12.0    True        False         False      18d
 ...output omitted...

    6. Use the get command to list pods in the openshift-api project. Specify the project with the -n option.

       [student@workstation ~]$ oc get pods -n openshift-apiserver
 NAME                         READY   STATUS    RESTARTS   AGE
 apiserver-68c9485699-ndqlc   2/2     Running   2          18d

    7. Use the oc status command to retrieve the status of resources in the openshift-authentication project.

       [student@workstation ~]$ oc status -n openshift-authentication
 In project openshift-authentication on server https://api.ocp4.example.com:6443

 https://oauth-openshift.apps.ocp4.example.com (passthrough) to pod port 6443 (svc/oauth-openshift)
   deployment/oauth-openshift deploys quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:7d75...6c86
     deployment #7 running for 2 weeks - 1 pod
     deployment #6 deployed 2 weeks ago
     deployment #4 deployed 2 weeks ago
     deployment #3 deployed 2 weeks ago
     deployment #2 deployed 2 weeks ago
     deployment #1 deployed 2 weeks ago
 ...output omitted...

    8. Use the explain command to list the description and available fields for services resources.

       [student@workstation ~]$ oc explain services
 KIND:     Service
 VERSION:  v1

 DESCRIPTION:
      Service is a named abstraction of software service (for example, mysql)
      consisting of local port (for example 3306) that the proxy listens on, and
      the selector that determines which pods will answer requests sent through
      the proxy.

 FIELDS:
    apiVersion    <string>
      APIVersion defines the versioned schema of this representation of an
      object. Servers should convert recognized schemas to the latest internal
      value, and may reject unrecognized values.
 ...output omitted...

    9. Use the get command to list cluster nodes.

       [student@workstation ~]$ oc get nodes
 NAME       STATUS   ROLES                         AGE   VERSION
 master01   Ready    control-plane,master,worker   18d   v1.25.4+77bec7a

      A single node exists in the cluster.

Finish

On the workstation machine, use the lab command to complete this exercise. This step is important to ensure that resources from previous exercises do not impact upcoming exercises.

[student@workstation ~]$ lab finish cli-interfaces
openshift