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Now, besides the two kinds of communication,

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the two kinds of requests you could say,

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I already talked about,

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container to worldwide web

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and container to host machine,

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there is one other form of communication

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you could encounter in your Dockerized app

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and that would be that your application

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running inside of your container

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wants to talk to another container.

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Let's say we have another container

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with a sequel database inside of it.

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Could all the be container with a Mongo DB

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database in a DOE

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or any aggro container,

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which is running some service

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to which you want to talk

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from inside your other container.

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So in this case,

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our application in the middle container

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might want to talk to this sequel database

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in another container.

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So communication between multiple containers

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is also a quite common scenario

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and in general, building applications

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with multiple containers is quite common.

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Up to this point in this course,

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we always worked with one container, right?

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We dockerized one pipe snap

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or one note app

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because we always had very simple application steer.

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Now, even though the demo app

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we're going to use in this module

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is also still quite simple,

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it's at least a bit more complex

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because here we actually, will have a great example,

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a great use case, a great scenario,

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where we might want to use multiple containers.

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Because with Docker containers,

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it is strongly recommended

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and the best practice that every container

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should just do one main thing.

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So if you have a note application,

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which also needs a Mongo DB database,

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it is a recommendation

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and the best practice that your note application,

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so does app JS file

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and all the required dependencies

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and Alden and models folder,

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which belongs to this app,

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go into one container and one image

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and your Mongo DB database uses another image

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and runs in another container.

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This is a best practice,

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and we're going to learn way more about

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multi container apps throughout this course.

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But this here is already a first example

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and therefore this example

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as well as most applications

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you're going to build with Docker,

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will typically need cross container communication

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and that will therefore be another form of communication

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and of networking,

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which we're going to take a closer look at

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in this module.