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Hello and welcome to this lecture.



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My name is Mumshad Mannambeth.



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In this lecture



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we will discuss about Kubernetes Deployments. For a minute,



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let us forget about PODs and replicasets and other kubernetes concepts and talk about how you might



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want to deploy your application in a production environment.



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Say for example 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 for obvious reasons.



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Secondly whenever newer versions of application builds become available on the docker registry you would



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like to upgrade your Docker instances seamlessly.



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However when you upgrade your instances you do not want to upgrade all of them at once



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as we just did. This may impact users accessing our applications, so you might want to upgrade them one



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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 and you're asked to undo the



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recent change you would like to be able to roll back the changes that were recently carried out. Finally,



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say for example you would like to make multiple changes to your environment such as upgrading the underlying



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



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WebServer versions, 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 you would like to



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apply a pause to your environment, make the changes and then resume so that all changes are rolled-out



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together. All of these capabilities are available with the kubernetes Deployments. So far in this course



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we discussed about PODs, which deploy single instances of our application such as the web application



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in this case. Each container is encapsulated in PODs. Multiple such PODs are deployed using Replication



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Controllers or Replica Sets. And then comes Deployment which is a kubernetes object that comes higher



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in the hierarchy.



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The deployment provides us with the capability to upgrade the underlying instances seamlessly using



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rolling updates, undo changes, and pause and resume changes as required.



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So how do we create a deployment. As with the previous components,



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We first create a deployment definition file. The contents of the deployment definition file are exactly



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similar to the replica set definition file, except for the kind, which is now going to be deployment. If



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we walk through the contents of the file



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it has an apiVersion which is apps/v1, metadata which has name and labels and a spec that



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has template, replicas and selector.



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The template has a pod definition inside it. Once the file is ready run the kubectl create command



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and specify the deployment definition file. Then run the kubectl get deployments command to see



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the newly created deployment. The deployment automatically creates a replica set.



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So if you run the kubectl get replcaset command



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You will be able to see a new replica set 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 difference between replica set and deployments except for the fact



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that deployments created a new kubernetes object called deployments.



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We will see how to take advantage of the deployment using the use cases we discussed in the previous



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slide in the upcoming lectures and one more note before we end this lecture.



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To see all the created objects at once run the kubectl get all command and in this case we can



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see that the deployment was created and then we have the replica set followed by three pods that were



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created as part of the deployment.



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That's it for this lecture.