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Now, to see this in action,

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for the moment,

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I will stick to this application we worked on thus far

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in this course.

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Just make sure that you've got no ongoing deployments

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with kubectl get deployments

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and you shouldn't see anything here.

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If you do, use the kubectl delete deployment command

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and then specify the name of the deployment to delete it.

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Also, make sure you've got no pods,

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which you shouldn't have if you have no deployments.

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And you've got no services,

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except for that default Kubernetes services,

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which is fine.

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Of course, also ensure that minikube is still up

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and running but if it wouldn't be,

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these commands I just showed you would have failed anyways.

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And with that, let's now create a config file

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for the deployment,

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which we created in the command line before.

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For this, I'll add a new file in this project

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and I'll name it deployment.yaml.

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The file name is totally up to you though.

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The only thing that matters

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is that it's a YAML file

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but the file name is up to you.

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Now, in this deployment.yaml file,

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we now specify how our deployment should look like,

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how it should work,

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how it should be configured.

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And there is a certain syntax you have to use

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in these Kubernetes config files.

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First of all, no matter which kind

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of resource you are configuring,

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if it's a deployment or a service,

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whatever it is, you need to specify an apiVersion

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by adding such an apiVersion key written like this.

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Now, there are different apiVersions available

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and like everything in the world,

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Kubernetes, of course,

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also is under active development.

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To find out which apiVersion to use here,

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my personal approach is that I dive into the docs

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or that I simply google for Kubernetes deployment YAML

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or something like this.

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You could also search for service.yaml

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if you would want to define a service

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and then somewhere in the docs,

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you will find an example snippet like this one

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and you'll see the apiVersion here.

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This is a quick way of finding out

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what the currently latest apiVersion is.

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Though, of course, you should keep in mind

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that if you always use the latest version,

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of course, some features might change over time.

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Here, I can use the latest version though

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and therefore, I set the apiVersion here

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to apps/v1 for this deployment resource,

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which I'm gonna create.

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And that's the next important piece

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of information we need here.

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Just because we named the file deployment

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does not mean that Kubernetes will treat it

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as a file that creates a deployment

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because we could have chosen any file name.

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Instead, you have to let Kubernetes know

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what you want to create

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by adding a kind key here.

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And that's super important.

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Here you define the kind

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of Kubernetes object you wanna create.

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And here, we wanna create a Deployment

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and of course, this value is not up to you.

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There's only a certain set of possible values here,

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like Service or Job, which we haven't used thus far.

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But in this case, we need a Deployment.

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And again, the official docs are a place

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where you can learn about all possible resource types

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and also very useful,

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in the official docs,

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at the very bottom here on the left, the reference.

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If you dive into the latest API reference here,

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you also find a full reference

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of all supported objects and configurations

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and for example, here, we can also dive

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into the Deployment object.

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Here we also see that it's apps v1 as a version.

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And then here, you see what you can configure

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in this YAML file.

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For example, here you also see the kind configuration,

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which here, of course, should be Deployment.

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So that's the next thing we set.

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Now, with that, we're telling Kubernetes

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that we wanna create a new deployment object.

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As a next step, you typically need

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to add some metadata.

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Now, this is not some random data you come up with

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but instead, this includes crucial things like the name

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of the object you're creating.

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And keep in mind, we chose a name

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in the imperative approach as well.

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There we created a deployment like this

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and we gave it a name like this.

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And here, we're basically doing the same.

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This deployment here is basically replaced

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by setting a kind here.

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And now we also need to give it a name

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so that we can identify it later.

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And we do this by adding the metadata key

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and then nest it in there

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and therefore, since it's YAML, indent it

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because that is how you nest things

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in a YAML document.

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We set a name.

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And now this name is totally up to you.

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I will name is second-app-deployment

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but this name again is up to you.

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Now, there is more metadata, which you can add.

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As you can see in the reference docs here

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on metadata, if you click on this type definition.

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It's not possible for all types

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but for many it is.

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And here you then see, if you scroll down below that list

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of objects which support this type,

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her you see what you can add.

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There you see you can add a lot,

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for example, the name, which we just added

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but also, other things,

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though I will say, many of these things don't need

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to be added for the vast majority of objects.

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And I will highlight some other things,

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which you can add whenever we have an object

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where it makes sense.

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So with that, I'll go back to my deployment definition here

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and just add the name here.

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Okay, so now we tell Kubernetes

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that we wanna create a deployment

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and that it will have a name of second-app-deployment.

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Now we need to add the so-called spec,

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the specification of this deployment.

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And that's the meat of this object

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because here, we will define how this deployment

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should be configured.

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So here, all the interesting things are being added

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and therefore, let's now dive into this.