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[Intro Music]

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Hello and welcome to this lecture.

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In this lecture, we will discuss about Kubernetes Deployments.

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For a minute, let us forget about PODs

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and ReplicaSets and other Kubernetes concepts,

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and talk about how you might want to deploy your application

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in a production environment.

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Say for example,

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you have a web server that needs to be deployed in a production environment.

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You need not one but many such instances of the web server running

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for obvious reasons.

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Secondly, whenever newer versions of application builds

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become available on the Docker registry,

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you would like to upgrade your Docker instances seamlessly.

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However, when you upgrade your instances,

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you do not want to upgrade all of them at once as we just did,

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this may impact users accessing our applications, so

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you might want to upgrade them one after the other,

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and that kind of upgrade is known as rolling updates.

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Suppose one of the upgrades you performed resulted in an unexpected error,

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and you're asked to undo the recent change,

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you would like to be able to rollback the changes that were recently carried out.

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Finally say for example, you would like to make

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multiple changes to your environment,

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such as upgrading the underlying web server versions,

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as well as scaling your environment and also modifying the resource allocations, etc.

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You do not want to apply each change immediately after the command is run, instead

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you would like to apply a pause to your environment,

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make the changes and then resume, so that

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all the changes are rolled out together.

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All of these capabilities are available with the Kubernetes Deployments.

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So far, in this course, we discussed about pods,

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which deploy single instances of our application,

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such as the web application in this case.

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Each container is encapsulated in pods.

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Multiple such pods are deployed using ReplicationControllers or ReplicaSets,

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and then comes deployment, which is a Kubernetes

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object that comes higher in the hierarchy.

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The deployment provides us with the capability

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to upgrade the underlying instances seamlessly using rolling updates,

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undo changes, and pause and resume changes as required.

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So how do we create a deployment?

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As with the previous components, we first create a deployment-definition file.

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The contents of the deployment-definition file

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are exactly similar to the replicaset-definition file,

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except for the kind, which is now going to be Deployment.

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If we worked through the contents of the file, it has an apiVersion,

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which is apps/v1;

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metadata, which has name and labels;

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and a spec that has template replicas and selector.

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The template has a pod definition inside it.

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Once the file is ready, run the kubectl

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create command and specify the deployment-definition file.

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Then run the kubectl get deployments command

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to see the newly created deployment.

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The Deployment automatically creates a ReplicaSet,

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so if you run the kubectl get replicaset command,

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you will be able to see a new ReplicaSet in the name of the Deployment.

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The ReplicaSets ultimately create pods;

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so if you run the kubectl get pods command,

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you will be able to see the pods with the name of the deployment and the ReplicaSet.

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So far, there hasn't been much of a

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difference between ReplicaSet and deployments,

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except for the fact that deployment

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created a new Kubernetes object called deployment.

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We will see how to take advantage of the deployment

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using the use cases we discussed in the previous slide in the upcoming lectures.

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And one more note before we end this lecture

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to see all the created objects at once

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run the kubectl get all command,

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and in this case, we can see that the deployment

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was created and then we have the ReplicaSet

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followed by three pods that were created as part of the deployment.

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[No Audio]

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That's it for this lecture, we will now head over to a demo

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and I will see you in the next lecture.

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[Outro Music]

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[No Audio]