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Hi, Let us understand about deployments. Earlier we discussed about replica sets

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which is going to have a collection of pods and it's going to maintain the

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desired capacity. Sometimes there may be a need to change the replica set and

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replace the replica set with a different version. Let's take an example I do have

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version one of application running with desired capacity as 3 and I'm going to

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get a different version of application or the next version of the application

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and I want that to get deploy. There are two ways of deploying, one: I can start 3

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such containers and replace all the requests coming to the old version

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to the newer version or I can go in a staggered way or in a controlled rate I can switch the traffic. So whenever

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I wanted to make change to the replica set in a controlled rate and in a controlled

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way I can go ahead and use the deployments. So deployment is nothing

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but it's a declarative way of controlling the pods or internally the replica sets

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and making sure the availability of the replica set is changed in a controlled rate

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and this can be used for different type of use cases like rolling the new version of

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replica sets or replacing the applications with a different version and facing out

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any version of the applications or pausing the entire application for some

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reason as well as to scale up or scale down the load on any replica set

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Basically I'm going to control the pod or replica set in a declarative way and that's

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where the deployments will be used. As we discussed earlier directly we will not

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be controlling the replica set in production we will be using the

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deployments or the auto scaling. Let's go ahead and create a sample deployment

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As a part of kubernetes website I do have the github user content over here.

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I'm going to use the web link directly and use kubectl apply and see how it's going

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to work. Here I do have the api version and kind as deployment within spec I do

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have replica as 3 and selector I am using the app as nginx, so this is what the label

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will be used to do the selection and the new pod will get created using this

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specific template and it will be using this specific label and it will be using the

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container with the name nginx and image as this specific image and port 80 will

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get exposed. Let me go ahead and apply this particular file, so automatically the

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file will get referred and the deployment will get created. Let me go ahead and

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get the deployments so I do have a deployment where zero objects are ready

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and the desired capacity needs to be 3. I can go ahead and do the description of

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this specific deployment, I can get the deployment details using the describe

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command and get the information. So here I do have the details about the name

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in which namespace it got created what are all the annotations that is

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the api version and what is the selector, this is the important label it's going to

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use to select the pods and whether it is part of this specific deployment or not

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and 3 desired capacity, yes I do have 3 number of pods available and as a part

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of blue-green deployment as well as the deployment strategy we will be

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discussing about the rolling update and what these specific values are, this is

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just a quick introduction on various concepts and objects available as a part

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of kubernetes. Now let me go ahead and get the replica set available as a part of

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this specific deployment, so I can get the replica set so this is what the replica set

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name I am going to get, let me give the command get rs, so this is the replica set

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available as a part of the deployment. If I get into the description of the

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deployment here I will be having the new deployment that is active and there is no

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old deployments available. In case if I wanted to roll it to a new version I will be

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getting the new replica set name over here and their status and within the

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replica set I should have n number of pods I can go ahead and get the pods as

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well, let me use the command kubectl get pods so these are all the pods

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available as a part of the specific deployment and I can get the pods with a

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label. So all the pods should have that specific label app is equal to nginx. So

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this is what the app selector that's going to use to make it as a part of the

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deployment or the replica set. So what's going to happen it's going to use the

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replica set internally and make use of the desired capacity and the collection of

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pods how to use the label selector and get the n number of pods up and running

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The most of the use cases we will be using is the controlled way of deploying

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or making changes to the replica set or to the auto scaling we will be using the

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deployments. We can go ahead and scale up the deployments as well as

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scale down the deployments and make changes to the deployments at runtime

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all those we will be discussing it as a part of advanced discussion of

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deployments. So in a quick summary we have seen what is a deployment and how

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it is going to use replica sets and pods, label selector as a part

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of the deployment internally and in what use cases and how

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it will be used within the kubernetes.