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So let's use compose here in this project

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and you'll find this project attached

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and it is the project we built

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in the last course section.

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So we have a backend

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and we have a frontend

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and we got the docker files

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in the backend and frontend folders.

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So did we there

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also have these images prepared

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because as I mentioned,

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we'll need these docker files.

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Docker compose will not replace them.

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Now, how do we get started with docker compose then?

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Well, in your project folder,

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you create a docker-compose.yml or yamol file.

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The extension can be free or four characters.

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It's always a yamol file

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and yamol is just a specific text format

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where you use indentation

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to express dependencies

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between configuration options.

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You'll see it in action here.

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Now, in such a docker compose yamol file,

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you describe your multi container environment,

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your project setup,

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and you always start by defining a version here.

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Now you should get auto completion here, by the way,

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since we installed the docker extension,

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make sure you have

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that Docker extension installed

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in visual studio code

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and with that you will get all the completion here,

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which is very helpful.

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So we specify a version here

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and with version I don't mean a version

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for our app or our file here.

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Instead, we specify the version

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of the docker compose specification we wanna use

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and the version we defined here

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has an effect on the features

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we can use in this compose file

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because the docker compose specification

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and therefore the Syntex we have

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to use in this docker compose file

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is under active development

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and may change over time.

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So you can lock in a certain version up here

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so the docker knows which features are

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and are not available.

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And therefore it's able

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to execute your docker compose file correctly.

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Now you can visit docs.docker.com/compose/composed-file.

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And you will find a complete reference

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of all the configuration options

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you can set up in a composed file,

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and you also find the different

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compose specification versions,

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which are available.

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And obviously that will change over time.

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I'm using 3.8 when I'm recording this,

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there will be newer versions out

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when you're viewing this most likely.

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However, of course, a new version

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does not mean that everything changed

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maybe some tiny new features were added

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and to be honest,

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most of the features you can use

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most of the configurations you can add

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might not matter to your project.

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And that's an evernote

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I have about this site here.

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It's a huge list,

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a long list of configuration options

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you can add in your docker compose yamol file

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and you will not need all of them.

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You will only need a small subset

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for most applications

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but of course,

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in order to express any potential projects

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that you might have,

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you have a lot of configuration options here.

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Now you can use this as a backup reference.

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I just wanted to talk about these versions.

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And so they offer at the moment

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3.8 is the latest version I have available.

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And I will specify this here

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therefore, to inform docker

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that this is the version does file uses

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and to let docker know

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which features I therefore want to use

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and want to be able to use.

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So that is the first thing we have to add, the version,

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that next thing,

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the next configuration we have to add here

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is the services key

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And by the way,

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these key names of course

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have to be typed correctly

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because docker will look out for these keywords.

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So this has to be version

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and not Version like this

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or VRS like this.

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It has to be written exactly like that.

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That's why it is auto-completion

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with the docker extension helps.

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So here we got services

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and now services doesn't take a value like this.

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Instead it has a couple of nested values.

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So we enter a new line

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and now the indentation here matters.

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I did indent by two blanks here.

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And this is important

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because yamol uses indentation

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to express dependencies

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and everything which is indented by two blanks

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is now a direct child of services

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and services needs

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at least one child element

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possibly multiple children.

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Now what are the children of services though?

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That will be your containers.

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And since our application here

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has three containers,

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we will have three child elements here below services.

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Now you can choose names

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of your choice to label these containers

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to give these containers a name.

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And I will name one container backend,

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one container frontend,

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and maybe first one container mongodb.

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Now these names are up to you.

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You can use any names you want here.

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They should all be on the same level though.

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All indented by two blanks,

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since they all are equal children to services.

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With that we're defining

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that our application, our project

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will use three containers.

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Now of course that's just the start.

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Now we can define a configuration

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for every container

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and you might already be guessing it.

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We do that by indenting again.

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So now I indent here below mongodb

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to set up the options

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that belong to the mongodb container.

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And we'll do something similar

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for backend and for frontend

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we'll indent by two more blanks here.

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So four blanks in total,

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and then that's the configuration

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for mongodb, backend and so on.

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So that's what we'll continue with

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because now we can dive into the configurations

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for the individual containers.