Introduction to Kubernetes¶
Kubernetes is a container orchestration system for automating the management of containers, storage and configuration of applications. Kubernetes manages one or more computers into a cluster which can run container-based workloads. Kubernetes is one of the most widely deployed pieces of software in the world, meaning it is available on any cloud and can be deployed to any computer.
Concepts¶
Kubernetes provides many basic building blocks, but this introduction will focus on those most relevant to running containers and applications.
- Pods - A Pod is a container running in the Kubernetes cluster.
- Control Plane - The Kubernetes control plane provides an API which can be used to manage the rest of the system.
- Nodes - A Node is a computer that is a member of the cluster, which the Control Plane can use to deploy workloads.
- Namespaces - Nearly everything in Kubernetes is separated into Namespaces, which are a way to divide your cluster resources into logical units. For example, if you run a blog and a landing page on your cluster, you might have those two workloads separated into blog and landing namespaces.
- Services - A Service provides an endpoint to connect to a group of Pods that provide one overall service.
- Volumes - A volume is a persistent storage location to be attached to Pods.
Creating a Kubernetes Cluster¶
If this is your first time using Kubernetes or Podinate, try going through the Podinate Quick Start guide to install a Kubernetes cluster and Podctl.
kubectl¶
Kubernetes provides an official CLI tool for interacting with the Kubernetes Control Plane, called Kubectl. Kubectl provides a handful of commands that can be applied to any type of Object in the Kubernetes cluster:
- get [type] - Show a list of all objects of the given type, for example kubectl get pods.
- describe [type] [name] - Get details of the given object, for example kubectl describe pod my-app.
- apply -f [file] - Apply a file of YAML or JSON definitions of Kubernetes objects. They will be created or updated to match the desired state.
Kubectl and Namespaces¶
Most resources in Kubernetes are divided into Namespaces, which allows you to group related resources on the cluster. There is also a default Namespace, called default.
Access objects in a specific namespace:
Keeping-n my-app at the start of the command allows you to easily edit the end of the command to change what kubectl is doing.
Access objects in all namespaces:
Unfortunately, -A needs to be placed after the sub-command name.You can also set which Namespace Kubectl will use if none is specified like so:
This is useful because most of the time you'll be interacting with one namespace for a long time, for example while deploying and debugging a particular app.