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For the spec, the specification

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of this object, we again have a nested key.

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So we indent

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below spec here,

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and we then add a couple of pieces of information

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about this deployment.

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For example, the number of pod instances

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we wanna have as a default.

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Now, if you don't add any information

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the default is one,

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but you can also manually set it

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by adding the replicas key here,

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and give that a value of one, or two, or three, or even zero

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if you initially don't want any pods to be launched.

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I'll set it to one, but you could also set it to three

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to start with three running pods,

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three equal pods containing the same container,

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right from the start.

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Which of course could make sense for certain applications.

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If you know that for the traffic which you expect

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to arrive you will need three pods anyways,

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you of course don't have to scale them after you created

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the deployment, you can simply start with three.

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But here we'll start with one, because of course,

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for our local development, this will suffice.

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Now as our next step, you need to add a template.

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Here You will define the pods that should be created

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as part of this deployment.

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And that's of course, super important.

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With the imperative approach, create deployment first app,

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we added "dash dash image" to define

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which image should be used for the container used

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in the pod attached to this deployment.

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Now we'll do kind of the same here.

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Now with the template we define the pod

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which should be created and therefor nested below template,

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we now also, again, add "metadata"

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because a pod is a new object in the Kubernetes World.

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Deployment is an object, a pod is another object,

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and therefore, we need new metadata here

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for this new object.

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To, for example, give it a name if you want to,

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but in this case, we want to add a label

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and we do this with the labels key.

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I'll come back to why we need a label in a second.

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For the moment, let's add it and nested below that,

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you can give it any label you want.

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And here both the key as well as the "value" value,

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are up to you.

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So here I'll name this app, "second dash app",

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but you could have also named this here, "deployment"

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or "depl"

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or... "tier"

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whatever you want.

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I'll add a label named "app" and give it a value

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of second app.

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And again I will come back to

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why labels are important metadata for some objects,

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in a second.

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Now, as a side note, you don't need to add the kind here

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because the template of a deployment always describes a pod.

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So this always is a pod object,

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and that's why we don't need to add this pod kind here.

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Indeed, if you have a look at the reference documentation,

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here in the deployment spec, and then there

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on the template,

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you see, this is always a pod template spec

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and therefor here, you see, you only can add two pieces

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of data, and that's the metadata and

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then the specification of the pod.

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And you can't even add a kind here because it's not expected

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by Kubernetes because this always has to be a pod.

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So we added the metadata, but as we just saw the other thing

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which we have to add for this pod template is

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the specification for how this pod should look like.

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We did add a specification before, this one,

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but that was the specification for the overall deployment.

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Now we add another spec on the same level

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as metadata inside of the template,

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so indented below template and here we now define

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how this pod should be configured.

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So this spec is the configuration of the deployment,

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which basically sets up which pod we want and how many pods.

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Now we have to specification of the individual pods

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which are created for this deployment.

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And here it's one type of pod per deployment.

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So you can have multiple pods if you increase the replicas

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but it's always the same pods then

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with the same containers inside of it.

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If you want different pods with different containers,

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you need different deployments.

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And we'll see that in action later as well.

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So here in this specification for the pod,

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we now basically need one important key

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and that's the containers key.

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And again, you can always look this up

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in the official documentation.

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If we have a look at the pod spec,

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we see that there's a lot we can configure,

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many things which you will rarely need,

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and basically nothing we need right now.

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But we do need this containers key here

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which allows us to define the containers

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or the single container, which should be part of this pod.

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Now we'll have a look at some of the other options later.

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For the moment, let's just add containers

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and there, we now have a list of containers,

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which means we need dashes.

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Without a dash it's just a nested key below another key.

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Now here, we can have multiple containers in the same pod,

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so you can have multiple containers to find

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with multiple dashes here, with multiple list items.

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And every container then can have a name,

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which is up to you.

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I will name it,

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"second node".

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Not because it's on the second worker node

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or anything like that, but because it's a Node.js app

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and it's our second app and the container

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for this second app.

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The name is up to you, of course.

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Very important is another key which you now don't add

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00:06:07,210 --> 00:06:10,160
with a dash because it's still for the same container,

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just in a new line.

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And that's the image which you want to use here.

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And of course, that's the image you would have specified

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with "dash dash image" here

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when creating a deployment imperatively.

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There, as a side note, you could have also

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added multiple images by separating them

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with commas to create multiple containers.

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Here in the declarative approach, as mentioned before,

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you could add multiple containers like this

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by adding multiple dashes.

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Not something we need to do here though,

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so I'll comment this out.

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Here the image I want to use, of course,

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00:06:47,320 --> 00:06:48,580
is the first...

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00:06:49,550 --> 00:06:52,000
app image I deployed before.

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So the "kub dash first app" image.

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00:06:54,540 --> 00:06:57,150
And it needs to be an image on a registry,

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00:06:57,150 --> 00:07:00,960
so that's why I'm using my registry account name here

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slash and then the image name.

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00:07:02,740 --> 00:07:05,770
So overall the repository name on that image.

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00:07:05,770 --> 00:07:08,540
And you can, of course, also specify a tag here

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00:07:08,540 --> 00:07:10,620
like that latest version we deployed

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00:07:10,620 --> 00:07:12,620
in one of the last lectures.

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00:07:12,620 --> 00:07:15,840
And that's it, that's the bare minimum configuration

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00:07:15,840 --> 00:07:18,660
we need here to create a deployment,

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00:07:18,660 --> 00:07:21,094
which will create one pod with that one container

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00:07:21,094 --> 00:07:23,010
inside of it.

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00:07:23,010 --> 00:07:25,330
That of course leaves only one question.

153
00:07:25,330 --> 00:07:28,730
How can we now apply that deployment?

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00:07:28,730 --> 00:07:31,530
How can we now make the cluster aware of it

155
00:07:31,530 --> 00:07:34,490
and have it create that deployment and pod

156
00:07:34,490 --> 00:07:36,290
and launch that container?

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00:07:36,290 --> 00:07:38,670
Well for that, we use the command line

158
00:07:38,670 --> 00:07:41,870
and we still use the kube control command here

159
00:07:41,870 --> 00:07:44,063
because that is our communication device

160
00:07:44,063 --> 00:07:46,220
with the master node.

161
00:07:46,220 --> 00:07:51,220
But now we don't call, create something, but instead, apply.

162
00:07:51,310 --> 00:07:52,920
That's another command built

163
00:07:52,920 --> 00:07:56,200
into this kube control command tool here,

164
00:07:56,200 --> 00:07:59,590
and it's simply applies a configuration file

165
00:07:59,590 --> 00:08:02,090
to the connected cluster.

166
00:08:02,090 --> 00:08:05,840
You identify the file with the dash F...

167
00:08:05,840 --> 00:08:06,890
option here

168
00:08:06,890 --> 00:08:09,490
and you can have multiple dash F options,

169
00:08:09,490 --> 00:08:12,190
if you wanna apply multiple files at once.

170
00:08:12,190 --> 00:08:14,270
Here, it's only one file though.

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00:08:14,270 --> 00:08:17,970
And then you simply add an equal sign and then the file name

172
00:08:17,970 --> 00:08:21,410
or the path to the file, which should be applied.

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00:08:21,410 --> 00:08:23,740
So in this case kube control applied

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00:08:23,740 --> 00:08:27,250
dash F equals deployment dot yaml.

175
00:08:27,250 --> 00:08:30,723
And if we now hit enter, it tries to apply this.

176
00:08:31,660 --> 00:08:33,820
But you see, I get an error.

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00:08:33,820 --> 00:08:37,130
I'm getting a missing required field "selector" here.

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00:08:37,130 --> 00:08:40,230
And I did this on purpose because selectors are

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00:08:40,230 --> 00:08:43,120
a key concept in the Kubernetes world,

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00:08:43,120 --> 00:08:46,083
especially when using the declarative approach.