Kubernetes is an open source container orchestration system for managing containerized applications across multiple hosts in a cluster.

Kubernetes provides mechanisms for application deployment, scheduling, updating, maintenance, and scaling. A key feature of Kubernetes is that it actively manages containers to ensure that the state of the cluster always matches the user's expectations.

Kubernetes enables you to respond quickly to customer demand by scaling or rolling out new features. It also allows you to make full use of your hardware.

Kubernetes is the following:

• Lean: Lightweight, simple, and accessible
• Portable: Public, private, hybrid, and multi-cloud
• Extensible: Modular, pluggable, hookable, composable, and toolable
• Self-healing: Auto-placement, auto-restart, and auto-replication

Kubernetes builds on a decade and a half of experience at Google running production workloads at scale, combined with best-of-breed ideas and best practices from the community:

Figure 1.1 – A 10,000-foot view of Kubernetes' architecture

One of the ways to manage Kubernetes clusters is kubectl—Kubernetes' command-line tool for management, it is a tool for accessing a Kubernetes cluster that allows you to run different commands against Kubernetes clusters to deploy apps, manage nodes, troubleshoot deployments, and more.

In this chapter, we're going to cover the following main topics:

• Introducing kubectl
• Installing kubectl
• kubectl commands

To learn kubectl, you will need access to a Kubernetes cluster; it can be one of these cloud ones:

• Google Cloud GKE: https://cloud.google.com/kubernetes-engine
• Azure AKS EKS: https://azure.microsoft.com/en-us/free/kubernetes-service
• AWS EKS: https://aws.amazon.com/eks/
• DigitalOcean DOKS: https://www.digitalocean.com/docs/kubernetes/

Alternatively, it can be a local one:

• KIND: https://kind.sigs.k8s.io/docs/user/quick-start/
• Minikube: https://kubernetes.io/docs/setup/learning-environment/minikube/
• Docker Desktop: https://www.docker.com/products/docker-desktop

In this book, we are going to use Google Cloud's GKE Kubernetes cluster.

You can use kubectl to deploy applications, inspect and manage them, check cluster resources, view logs, and more.

kubectl is a command-line tool that can run from your computer, in CI/CD pipelines, as part of the operating system, or as a Docker image. It is a very automation-friendly tool.

kubectl looks for a configuration file named .kube in the $HOME folder. In the .kube file, kubectl stores the cluster configurations needed to access a Kubernetes cluster. You can also set the KUBECONFIG environment variable or use the --kubeconfig flag to point to the kubeconfig file.

Let's take a look at how you can install kubectl on macOS, on Windows, and in CI/CD pipelines.

Installing on macOS

The easiest way to install kubectl on macOS is using the Homebrew package manager (https://brew.sh/):

1. To install, run this:

   $ brew install kubectl

2. To see the version you have installed, use this:

   $ kubectl version –client --short
   Client Version: v1.18.1

Installing on Windows

To install kubectl on Windows, you could use the simple command-line installer Scoop (https://scoop.sh/):

1. To install, run this:

   $ scoop install kubectl

2. To see the version you have installed, use this:

   $ kubectl version –client --short
   Client Version: v1.18.1

3. Create the .kube directory in your home directory:

   $ mkdir %USERPROFILE%\.kube

4. Navigate to the .kube directory:

   $ cd %USERPROFILE%\.kube

5. Configure kubectl to use a remote Kubernetes cluster:

   $ New-Item config -type file

Installing on Linux

When you want to use kubectl on Linux, you have two options:

• Use curl:

  $ curl -LO https://storage.googleapis.com/kubernetes-release/release/`curl -s https://storage.googleapis.com/kubernetes-release/release/stable.txt`/bin/linux/amd64/kubectl

• If your Linux system supports Docker images, use https://hub.docker.com/r/bitnami/kubectl/.

  Note

  Linux is a very common environment for CI/CD pipelines.

To get a list of supported kubectl commands, run this:

$ kubectl --help

kubectl commands are grouped by category. Let's look at each category.

Basic commands

The following are basic kubectl commands:

• create: Create a resource from a file or from stdin; for example, create a Kubernetes deployment from the file.
• expose: Take a 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—for example, set environment variables, update a Docker image in a pod template, and so on.
• explain: Get the documentation of resources—for example, the documentation on deployments.
• get: Display one or many resources. For example, you can get a list of running pods or the YAML output of a pod.
• edit: Edit a resource—for example, edit a deployment.
• delete: Delete resources by filenames, stdin, resources, and names, or by resources and label selectors.

Deploy commands

The following are kubectl deploy commands:

• rollout: Manage the rollout of a resource.
• scale: Set a new size for a deployment, ReplicaSet, or StatefulSet.
• autoscale: Auto-scale a deployment, ReplicaSet, or StatefulSet.

Cluster management commands

The following are the kubectl cluster management commands:

• certificate: Modify certificate resources.
• cluster-info: Display cluster information.
• top: Display resource (CPU/memory/storage) usage.
• cordon: Mark a node as unschedulable.
• uncordon: Mark a node as schedulable.
• drain: Drain a node in preparation for maintenance.
• taint: Update the taints on one or more nodes.

Troubleshooting and debugging commands

The following are the kubectl troubleshooting and debugging commands:

• describe: Show the details of a specific resource or group of resources.
• logs: Print the logs for a container in a pod.
• attach: Attach to a running container.
• exec: Execute a command in a container.
• port-forward: Forward one or more local ports to a pod.
• proxy: Run a proxy to the Kubernetes API server.
• cp: Copy files and directories to and from containers.
• auth: Inspect authorization.

Advanced commands

The following are the kubectl advanced commands:

• diff: Show difference of live version against a would-be applied version.
• apply: Apply a configuration to a resource by filename or stdin.
• patch: Update the field(s) of a resource using a strategic merge patch.
• replace: Replace a resource by filename or stdin.
• wait: Wait for a specific condition on one or many resources.
• convert: Convert config files between different API versions.
• kustomize: Build a kustomization target from a directory or a remote URL.

Settings commands

The following are the settings commands in kubectl:

• label: Update the labels on a resource.
• annotate: Update the annotations on a resource.

Other commands

The following are several other commands used in kubectl:

• alpha: Commands for features in alpha.
• api-resources: Print the supported API resources on the server.
• api-versions: Print the supported API versions on the server, in the form of group/version.
• config: Modify kube-config files.
• plugin: Provide utilities for interacting with plugins.
• version: Print the client and server version information.

As you can see from the lists, commands are divided into different groups. We are going to learn about most but not all of these commands in the coming chapters.

At the time of writing, the kubectl version is 1.18; with more recent versions, the commands might have changed.

In this chapter, we have learned what kubectl is and how to install it on macOS, Windows, and CI/CD pipelines. We also checked out the different commands supported by kubectl and what they do.

In the next chapter, we will learn how to get information about Kubernetes clusters using kubectl.