Exercise - Explore the functionality of a Kubernetes cluster

  • 15 minutes

Several options are available when you're running Kubernetes locally. You can install Kubernetes on physical machines or VMs, or use a cloud-based solution such as Azure Kubernetes Service (AKS).

Your goal in this exercise is to explore a Kubernetes installation with a single-node cluster. In this exercise, you learn how to configure and install a MicroK8s environment that's easy to set up and tear down. Then, you deploy a Kubernetes service and scale it out to multiple instances to host a website.

Note

This exercise is optional and includes steps that show how to delete and uninstall the software and resources you'll use in the exercise.

Keep in mind that there are other options, such as MiniKube and Kubernetes support in Docker, to do the same.

What is MicroK8s?

MicroK8s is an option for deploying a single-node Kubernetes cluster as a single package to target workstations and Internet of Things (IoT) devices. Canonical, the creator of Ubuntu Linux, originally developed and currently maintains MicroK8s.

You can install MicroK8s on Linux, Windows, and macOS. However, installation instructions are slightly different for each operating system. Choose the option that best fits your environment.

Install MicroK8s on Linux

The Linux installation of MicroK8s is the installation option that has the lowest number of steps. Switch to a terminal window and run the commands in the following instructions:

  1. Install the MicroK8s snap app. This step might take a few minutes to complete, depending on the speed of your internet connection and desktop.

    sudo snap install microk8s --classic

    A successful installation shows the following message.

    2020-03-16T12:50:59+02:00 INFO Waiting for restart...
microk8s v1.17.3 from Canonical✓ installed

You're now ready to install add-ons on the cluster.

Install MicroK8s on Windows

To run MicroK8s on Windows, use Multipass. Multipass is a lightweight VM manager for Linux, Windows, and macOS.

  1. Download and install the latest release of Multipass for Windows from GitHub.

  2. In a command console, run the Multipass launch command to configure and run the microk8s-vm image. This step might take a few minutes to complete, depending on the speed of your internet connection and desktop.

    multipass launch --name microk8s-vm --memory 4G --disk 40G

  3. After you receive the launch confirmation for microk8s-vm, run the multipass shell microk8s-vm command to access the VM instance.

    multipass shell microk8s-vm

    Once multipass is working, you can access the Ubuntu VM to host your cluster and install MicroK8s.

  4. Install the MicroK8s snap app. This step might take a few minutes to complete, depending on the speed of your internet connection and desktop.

    sudo snap install microk8s --classic

    A successful installation shows the following message:

    2020-03-16T12:50:59+02:00 INFO Waiting for restart...
microk8s v1.17.3 from Canonical✓ installed

You're now ready to install add-ons on the cluster.

Install MicroK8s on macOS

To run MicroK8s on macOS, use Multipass. Multipass is a lightweight VM manager for Linux, Windows, and macOS.

  1. You have two options to install Multipass on macOS. Either download and install the latest release of Multipass for macOS from GitHub, or to install Multipass with the brew cask install multipass command, use Homebrew.

    brew install --cask multipass

  2. In a command console, run the multipass launch command to configure and run the microk8s-vm image. This step might take a few minutes to complete, depending on the speed of your internet connection and desktop.

    multipass launch --name microk8s-vm --memory 4G --disk 40G

  3. After you receive the launch confirmation for microk8s-vm, run the multipass shell microk8s-vm command to enter the VM instance.

    multipass shell microk8s-vm

    At this point, you can access the Ubuntu VM to host your cluster. You still have to install MicroK8s. Follow these steps.

  4. Install the MicroK8s snap app. This step might take a few minutes to complete, depending on the speed of your internet connection and desktop.

    sudo snap install microk8s --classic

    A successful installation shows the following message:

    2020-03-16T12:50:59+02:00 INFO Waiting for restart...
microk8s v1.17.3 from Canonical✓ installed

You're now ready to install add-ons on the cluster.

Prepare the cluster

To view the status of the installed add-ons on your cluster, run the status command in MicroK8s. These add-ons provide several services, some of which you covered previously. One example is DNS functionality.

  1. To check the status of the installation, run the microk8s.status --wait-ready command.

    sudo microk8s.status --wait-ready

    Notice that there are several disabled add-ons on your cluster. Don't worry about the add-ons that you don't recognize.

    microk8s is running
addons:
cilium: disabled
dashboard: disabled
dns: disabled
fluentd: disabled
gpu: disabled
helm3: disabled
helm: disabled
ingress: disabled
istio: disabled
jaeger: disabled
juju: disabled
knative: disabled
kubeflow: disabled
linkerd: disabled
metallb: disabled
metrics-server: disabled
prometheus: disabled
rbac: disabled
registry: disabled
storage: disabled

  2. From the list, you need to enable the DNS, Dashboard, and Registry add-ons. Here are the purposes of each add-on:

    Add-ons Purpose
    DNS Deploys the coreDNS service.
    Dashboard Deploys the kubernetes-dashboard service and several other services that support its functionality. It's a general-purpose, web-based UI for Kubernetes clusters.
    Registry Deploys a private registry and several services that support its functionality. To store private containers, use this registry.

    To install the add-ons, run the following command.

    sudo microk8s.enable dns dashboard registry

You're now ready to access your cluster with kubectl.

Explore the Kubernetes cluster

MicroK8s provides a version of kubectl that you can use to interact with your new Kubernetes cluster. This copy of kubectl allows you to have a parallel installation of another system-wide kubectl instance without affecting its functionality.

  1. Run the snap alias command to alias microk8s.kubectl to kubectl. This step simplifies usage.

    sudo snap alias microk8s.kubectl kubectl

    The following output appears when the command finishes successfully:

    Added:
  - microk8s.kubectl as kubectl

Display cluster node information

Recall from earlier that a Kubernetes cluster exists out of control planes and worker nodes. Let's explore the new cluster to see what's installed.

  1. Check the nodes that are running in your cluster.

    You know that MicroK8s is a single-node cluster installation, so you expect to see only one node. Keep in mind, though, that this node is both the control plane and a worker node in the cluster. Confirm this configuration by running the kubectl get nodes command. To retrieve information about all the resources in your cluster, run the kubectl get command:

    sudo kubectl get nodes

    The result is similar to the following example, which shows you that there's only one node in the cluster with the name microk8s-vm. Notice that the node is in a Ready state. The ready state indicates that the control plane might schedule workloads on this node.

    NAME          STATUS   ROLES    AGE   VERSION
microk8s-vm   Ready    <none>   35m   v1.17.3

    You can get more information for the specific resource that's requested. For example, let's assume that you need to find the node's IP address. To fetch extra information from the API server, run the -o wide parameter:

    sudo kubectl get nodes -o wide

    The result is similar to the following example. Notice that you now can see the node's internal IP address, the OS running on the node, the kernel version, and the container runtime.

    NAME          STATUS   ROLES    AGE   VERSION   INTERNAL-IP      EXTERNAL-IP   OS-IMAGE             KERNEL-VERSION      CONTAINER-RUNTIME
microk8s-vm   Ready    <none>   36m   v1.17.3   192.168.56.132   <none>        Ubuntu 18.04.4 LTS   4.15.0-88-generic   containerd://1.2.5

  2. The next step is to explore the services running on your cluster. As with nodes, to find information about the services running on the cluster, run the kubectl get command.

    sudo kubectl get services -o wide

    The result is similar to the following example, but notice that only one service is listed. You installed add-ons on the cluster earlier, and you'd expect to see these services as well.

    NAME         TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)   AGE   SELECTOR
kubernetes   ClusterIP   10.152.183.1   <none>        443/TCP   37m   <none>

    The reason for the single service listing is that Kubernetes uses a concept called namespaces to logically divide a cluster into multiple virtual clusters.

    To fetch all services in all namespaces, pass the --all-namespaces parameter:

    sudo kubectl get services -o wide --all-namespaces

    The result is similar to the following example. Notice that you have three namespaces in your cluster. They're the default, container-registry, and kube-system namespaces. Here, you can see the registry, kube-dns, and kubernetes-dashboard instances that you installed. There are also supporting services that were installed alongside some of the add-ons.

    NAMESPACE            NAME                        TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)                  AGE   SELECTOR
container-registry   registry                    NodePort    10.152.183.36    <none>        5000:32000/TCP           28m   app=registry
default              kubernetes                  ClusterIP   10.152.183.1     <none>        443/TCP                  37m   <none>
kube-system          dashboard-metrics-scraper   ClusterIP   10.152.183.130   <none>        8000/TCP                 28m   k8s-app=dashboard-metrics-scraper
kube-system          heapster                    ClusterIP   10.152.183.115   <none>        80/TCP                   28m   k8s-app=heapster
kube-system          kube-dns                    ClusterIP   10.152.183.10    <none>        53/UDP,53/TCP,9153/TCP   28m   k8s-app=kube-dns
kube-system          kubernetes-dashboard        ClusterIP   10.152.183.132   <none>        443/TCP                  28m   k8s-app=kubernetes-dashboard
kube-system          monitoring-grafana          ClusterIP   10.152.183.88    <none>        80/TCP                   28m   k8s-app=influxGrafana
kube-system          monitoring-influxdb         ClusterIP   10.152.183.232   <none>        8083/TCP,8086/TCP        28m   k8s-app=influxGrafana

    Now that you can see the services running on the cluster, you can schedule a workload on the worker node.

Install a web server on a cluster

You want to schedule a web server on the cluster to serve a website to your customers. You can choose from several options. For this example, you use NGINX.

Recall from earlier that you can use pod manifest files to describe your pods, replica sets, and deployments to define workloads. Because you haven't covered these files in detail, you run kubectl to directly pass the information to the API server.

Even though the use of kubectl is handy, using manifest files is a best practice. Manifest files allow you to roll forward or roll back deployments with ease in your cluster. These files also help document a cluster's configuration.

  1. To create your NGINX deployment, run the kubectl create deployment command. Specify the name of the deployment and the container image to create a single instance of the pod.

    sudo kubectl create deployment nginx --image=nginx

    The result is similar to the following example:

    deployment.apps/nginx created

  2. To fetch the information about your deployment, run kubectl get deployments:

    sudo kubectl get deployments

    The result is similar to the following example. Notice that the name of the deployment matches the name you gave it, and that one deployment with this name is in a ready state and available.

    NAME    READY   UP-TO-DATE   AVAILABLE   AGE
nginx   1/1     1            1           18s

  3. The deployment created a pod. To fetch info about your cluster's pods, run the kubectl get pods command:

    sudo kubectl get pods

    The result is similar to the following example. Notice that the name of the pod is a generated value prefixed with the name of the deployment, and the pod has a status of Running.

    NAME                     READY   STATUS    RESTARTS   AGE
nginx-86c57db685-dj6lz   1/1     Running   0          33s

Test the website installation

Test the NGINX installation by connecting to the web server through the pod's IP address.

  1. To find the pod's address, pass the -o wide parameter:

    sudo kubectl get pods -o wide

    The result is similar to the following example. Notice that the command returns both the IP address of the node, and the node name on which the workload is scheduled.

    NAME                     READY   STATUS    RESTARTS   AGE     IP           NODE          NOMINATED NODE   READINESS GATES
nginx-86c57db685-dj6lz   1/1     Running   0          4m17s   10.1.83.10   microk8s-vm   <none>           <none>

  2. To access the website, run wget on the IP listed before:

    wget <POD_IP>

    The result is similar to the following example:

    --2020-03-16 13:34:17--  http://10.1.83.10/
Connecting to 10.1.83.10:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 612 [text/html]
Saving to: 'index.html'

index.html                                    100%[==============================================================================================>]     612  --.-KB/s    in 0s

2020-03-16 13:34:17 (150 MB/s) - 'index.html' saved [612/612]

Scale a web server deployment on a cluster

Assume that you suddenly see an increase in users who access your website, and the website starts failing because of the load. You can deploy more instances of the site in your cluster and split the load across the instances.

To scale the number of replicas in your deployment, run the kubectl scale command. You specify the number of replicas you need and the name of the deployment.

  1. To scale the total of NGINX pods to three, run the kubectl scale command:

    sudo kubectl scale --replicas=3 deployments/nginx

    The result is similar to the following example:

    deployment.apps/nginx scaled

    The scale command allows you to scale the instance count up or down.

  2. To check the number of running pods, run the kubectl get command, and again pass the -o wide parameter:

    sudo kubectl get pods -o wide

    The result is similar to the following example. Notice that you now see three running pods, each with a unique IP address.

    NAME                     READY   STATUS    RESTARTS   AGE     IP           NODE          NOMINATED NODE   READINESS GATES
nginx-86c57db685-dj6lz   1/1     Running   0          7m57s   10.1.83.10   microk8s-vm   <none>           <none>
nginx-86c57db685-lzrwp   1/1     Running   0          9s      10.1.83.12   microk8s-vm   <none>           <none>
nginx-86c57db685-m7vdd   1/1     Running   0          9s      10.1.83.11   microk8s-vm   <none>           <none>
ubuntu@microk8s-vm:~$

You'd need to apply several more configurations to the cluster to effectively expose your website as a public-facing website. Examples include installing a load balancer and mapping node IP addresses. This type of configuration forms part of advanced aspects that you'll explore in the future. In the summary, there are instructions if you choose to uninstall and clean up your VM.