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Kubernetes overview

What is Kubernetes?

Production-Grade Container Scheduling and Management

Kubernetes is an open source 'Production-Grade' container Orchestration platform. It can be used to automate deployment, scaling and management of containerized applications. With modern web services, users expect applications to be available 24/7, and developers expect to deploy new versions of those applications several times a day. Containerization helps package software to serve these goals, enabling applications to be released and updated in an easy and fast way without downtime. Kubernetes helps you make sure those containerized applications run where and when you want, and helps them find the resources and tools they need to work

One of the advantages of it being open source is that it gives you the freedom to run your workloads anywhere (on-premises, hybrid, or public cloud infrastructure).

In this workshop we are going to focus on the basics but the platform is fully extendable to suit a various number of use cases and work loads.

Kubernetes Basic Architecture

Kubernetes Architecture Diagram

More details about each components can be found at https://kubernetes.io/docs/concepts/overview/components/

Above is a basic diagram of some of the components that make up the platform. The master node is the brain of the platform. Users use the cli tool kubectl to interact with master node and it will provision your containers across the worker nodes. Each worker node is running an agent called kubelete which is interacting with the master node provision containers as necessary until the platform matches the state that you define. Kubernetes is a declarative API You will rarely ever interact with the worker nodes directly.

If you are looking to understand how to create your own kubernetes cluster read Kelsey Hightower's Kubernetes the hard way

Kubernetes Basics

All interactions in this workshop will be performed using the kubectl tool. https://kubernetes.io/docs/reference/kubectl/overview/

Use the following syntax to run commands

kubectl [command] [TYPE] [NAME] [flags]

You can also look at this as operations on a resource

For example:

kubectl     [Operations]    [Resource]
kubectl     get         nodes

There are a lot of action to choose from but some of the most commonly uses are

apply       - Apply a configuration change to a resource from a file or stdin.
create      - Create one or more resources from a file or stdin.
describe    - Display the detailed state of one or more resources.
get         - List one or more resources.
logs        - Print the logs for a container in a pod.

We will be going through various types of resources throughout this talk:

Let get a feel for some of these commands and what they do. Don't worry about understanding what is happening these are just to give you a feel for some of the actions that are performed using the commands.

kubectl apply -f resources/intro.yaml

To see everything

master $ kubectl get all
NAME                                    READY   STATUS    RESTARTS   AGE
pod/hello-world-deployment-785df54c5c-5lbz6   1/1     Running   0          94s
pod/hello-world-deployment-785df54c5c-c6vvc   1/1     Running   0          94s
pod/hello-world-deployment-785df54c5c-m7wfp   1/1     Running   0          94s

NAME                 TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
service/kubernetes   ClusterIP   10.96.0.1    <none>        443/TCP   21m

NAME                               READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/hello-world-deployment   3/3     3            3           94s

NAME                                          DESIRED   CURRENT   READY   AGE
replicaset.apps/hello-world-deployment-785df54c5c   3         3         3       94s

You can can get all of a specific resource. (adding -owide give you more information)

master $ kubectl get deployments -owide
NAME               READY   UP-TO-DATE   AVAILABLE   AGE    CONTAINERS   IMAGES    SELECTOR
hello-world-deployment   3/3     3            3           107s   intro        busybox   app=hello-world

You can use describe to find out more details about something running

master $ kubectl describe deployment hello-world-deployment
Name:                   hello-world-deployment
Namespace:              default
....

You can view the logs of a running pod

master $ kubectl get pods
NAME                                READY   STATUS    RESTARTS   AGE
hello-world-deployment-785df54c5c-5lbz6   1/1     Running   0          2m48s
hello-world-deployment-785df54c5c-c6vvc   1/1     Running   0          2m48s
hello-world-deployment-785df54c5c-m7wfp   1/1     Running   0          2m48s

master $ kubectl logs hello-world-deployment-785df54c5c-5lbz6
Hello Kubernetes!

Clean up

master $ k delete -f resources/intro.yaml
deployment.apps "hello-world-deployment" deleted

YAML

Kubernetes uses YAML files to define resources. Yaml is a serialization language that is intended to be human readable. YAML uses 2 space indentation. YAML is a superset of JSON Let quickly compare YAML and JSON:

---
title: Hitchhiker's Guide to the Galaxy
author: Douglas Adams
books: 
  - The Hitchhiker's Guide to the Galaxy
  - The Restaurant at the End of the Universe
  - Life, the Universe and Everything
  - So Long, and Thanks for All the Fish
  - Mostly Harmless
meaning:
  of:
    life: 42
{
  "title": "Hitchhiker's Guide to the Galaxy",
  "author": "Douglas Adams",
  "books": [
    "The Hitchhiker's Guide to the Galaxy",
    "The Restaurant at the End of the Universe",
    "Life, the Universe and Everything",
    "So Long, and Thanks for All the Fish",
    "Mostly Harmless"
  ],
  "meaning": {
    "of": {
      "life": 42
    }
  }
}

You will see a lot of YAML in the following pages

Next topic

Pods