Understand Kubernetes Object and Create Nginx Deployment

In this blog, we will explore Kubernetes Objects ,learn about how to create a Nginx deployment using yaml file.

We will also learn how to rollback the deployment and how the revision number changed when we do the rollback.

Prerequisite

  1. Kubernetes Cluster should be configured
  2. Kubectl configured

Follow my YouTube video or blog to setup the prerequisite.

Kubernetes Objects

Kubernetes objects are persistent entities in the Kubernetes system. Kubernetes uses these entities to represent the state of your cluster.

A Kubernetes object is a “record of intent” — once you create the object, the Kubernetes system will constantly work to ensure that object exists.

By creating an object, you’re effectively telling the Kubernetes system what you want your cluster’s workload to look like; this is your cluster’s desired state.

Kubernetes object includes two nested object fields that govern the object’s configuration: the object spec and the object status

Deploying workloads using YAML files

We will create the resource configurations required to deploy your applications in Kubernetes

Make sure you have a Kubernetes cluster ready and kubectl configured to manage the cluster resources.

Agenda:

  • Creating a Deployment
  • Verifying a Deployment
  • Editing a Deployment
  • Rolling back a Deployment
  • Deleting a Deployment

Creating a Deployment

A Deployment is an object that actually represents your application which is running on the cluster

We will create a Deployment using a yaml file where we will have configurations defined for our application like images, port, pods etc.

So let’s create a sample yaml file for the nginx deployment. You can also refer the git repo for this yaml file

apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
name: nginx-deployment
spec:
selector:
matchLabels:
app: nginx
replicas: 2 # tells deployment to run 2 pods matching the template
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: nginx:1.14.2
ports:
- containerPort: 80

Now, lets describe each tags in more detail

apiversion — Version of Kubernetes API

kind — Kind of object like Deployment/Service you want to create

metadata — to uniquely identify your object with tag name

spec — Desired state of your object by providing below details:

  1. .spec.selector how the Deployment finds which Pods to manage
  2. .spec.replicas how many pods

For more details on deployment refer official kubernetes documentation

Now Let’s create a deployment object using the yaml file

— -record This flag is used to write the command executed in the resource annotation kubernetes.io/change-cause.

kubectl apply -f nginx.yaml --record=true
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Now if you run the rollout history you will see the message

kubectl rollout history deployment.v1.apps/nginx-deployment
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Verify the Deployment

Let’s check the status of the deployment

kubectl get deployment
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Check the deployment status

kubectl rollout status deployment nginx-deployment
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Check the replica sets and pods which got deployed as part of this deployment

Replica Set — maintains a stable set of replica Pods running at any given time.

kubectl get rs,pods
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Edit the Deployment

Firstly, let’s add the annotation which will provide the description of your change

CHANGE-CAUSE is copied from the Deployment annotation kubernetes.io/change-cause to its revisions upon creation. You can specify theCHANGE-CAUSE message by:

kubectl annotate deployment nginx-deployment kubernetes.io/change-cause="initial deployment"kubectl rollout history deployment.v1.apps/nginx-deployment
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Now we will try to edit the deployment and scale it to 3

kubectl edit deployment nginx-deployment

Now check the rolling Status, you will see only one revision because scaling the Deployment, do not create a Deployment revision. Again, edit the deployment and change the image to the some other version you will see the new revision gets created.

kubectl rollout history deployment.v1.apps/nginx-deployment
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Describe Deployment

kubectl get deployment

Rolling Back Deployment

By default, all of the Deployment’s rollout history is kept in the system so that you can rollback anytime you want.

A Deployment’s revision is created when a Deployment’s rollout is triggered.

If you update the labels or container images of the template then only a new Deployment revision gets created.

Other updates, such as scaling the Deployment, do not create a Deployment revision.

Therefore, when you do the rollback to the previous version then only pod template gets rolled back but not the pod replica. If you have 3 pods running then after rollback also 3 pods will be running.

Now, let’s use the different image of nginx which is not available in dockerhub

using below command

kubectl set image deployment/nginx-deployment nginx=nginx:1.16.1.2 --record
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To fix the above issue you need to revert back to the previous version

kubectl rollout undo deployment nginx-deployment
kubectl rollout undo deployment nginx-deployment --to-revision=2

Refer their official documentation for Rolling Back Deployment here

Deleting a deployment

kubectl delete deployment nginx-deployment

Congratulations, we have successfully explore Kubernetes Objects , learn about how to create a nginx deployment using yaml file.

Written by

Devops Automation Enginneer

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