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Now that we learned about the crucial

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feature of volumes,

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persistent volumes,

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and persistent volume claims.

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The last topic I wanna cover in this course section

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would be environment variables.

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Because environment variables

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of course matter

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in a lot of applications.

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Let's say in this application here.

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The application we've been working on all the time.

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This story folder,

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in which we stored a text text file

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is of course hard-coded in the code.

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Now actually,

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the fact that

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we do store data in a story folder

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is however configured

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in our deployment yaml file, here.

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At least that is the folder

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which we save

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with help of a volume.

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So we might prefer

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to set up that exact folder name here

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in our yaml files,

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and use it through an environment variable

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inside of app JS.

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And we learned about applying environment variables

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with Docker and Docker compose.

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Of course, Kubernetes

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also supports environment variables.

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And for that,

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let's start the code.

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Here I will replace

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the hard-coded story

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folder name

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with process.env.STORY_FOLDER.

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This name is up to you.

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It's your program,

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it's your environment,

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the names are up to you.

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But of course now we need to ensure

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that this environment variable

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is set to a folder name

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we wanna use

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when we deploy our cluster.

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And therefore we need to provide a value

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for this environment variable.

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And the easiest way of doing that

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is to go to the file where you define your pod,

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and therefore the container,

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which is executed in the pod.

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So in our case, the deployment.yaml file,

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and in there,

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in your containers config,

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next to volume mounts,

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and image,

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and so on,

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you can add a env key.

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And below that,

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so indented below the env key

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you can set up all your environment key value pairs

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which you might need.

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Simply by adding a list of environment variables

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by using dashes here.

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So my first,

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and in this case only environment variable

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which I wanna set

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has a name,

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and that's something you need to provide

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the name of the environment variable

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of story underscore, folder.

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So that name you chose here in your code

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that's the name

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for the environment variable

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you wanna define here.

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And then of course, besides the name,

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we also need,

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a value.

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So that's the second key

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you need to provide for every environment variable.

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So name

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of the environment variable,

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and value

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for that environment variable.

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In this case, story.

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But of course you could choose a different name here,

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but then

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you should also bind a different folder

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with your

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volume here.

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But with that we now externalized this name,

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and we make it more flexible.

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Now, if we ever want to go for a different folder name

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we only need to make changes here

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in our

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containers pack,

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and we don't need to make any changes to app JS anymore

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because we are utilizing an environment variable here.

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Hence here now,

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if I

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update my image tag,

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or we set the image pull policy

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to always pull the updated image,

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which I don't have here,

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hence I changed the tag.

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Then we just need to

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build this image again,

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with a tag of academind/kub-data-demo,

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and then

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a tag of 2,

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so colon 2 here,

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hit enter,

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and once this is built, of course,

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docker push academind kub-data-demo,

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with tag 2.

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And now this is pushed to Docker Hub,

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so that now

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this will

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be pulled, and used

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if we apply our changes to the deployment.

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So let's wait for this push process to finish.

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And then let's apply this updated deployment.yaml file,

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so that the deployment is updated.

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Our old pods will be

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terminated eventually

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here you can see it,

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and the new pods are up and running.

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Now getting the data still works,

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and everything still works.

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But now under the hood,

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we are using our environment variables.