Now, besides the two kinds of communication,
the two kinds of requests you could say,
I already talked about,
container to worldwide web
and container to host machine,
there is one other form of communication
you could encounter in your Dockerized app
and that would be that your application
running inside of your container
wants to talk to another container.
Let's say we have another container
with a sequel database inside of it.
Could all the be container with a Mongo DB
database in a DOE
or any aggro container,
which is running some service
to which you want to talk
from inside your other container.
So in this case,
our application in the middle container
might want to talk to this sequel database
in another container.
So communication between multiple containers
is also a quite common scenario
and in general, building applications
with multiple containers is quite common.
Up to this point in this course,
we always worked with one container, right?
We dockerized one pipe snap
or one note app
because we always had very simple application steer.
Now, even though the demo app
we're going to use in this module
is also still quite simple,
it's at least a bit more complex
because here we actually, will have a great example,
a great use case, a great scenario,
where we might want to use multiple containers.
Because with Docker containers,
it is strongly recommended
and the best practice that every container
should just do one main thing.
So if you have a note application,
which also needs a Mongo DB database,
it is a recommendation
and the best practice that your note application,
so does app JS file
and all the required dependencies
and Alden and models folder,
which belongs to this app,
go into one container and one image
and your Mongo DB database uses another image
and runs in another container.
This is a best practice,
and we're going to learn way more about
multi container apps throughout this course.
But this here is already a first example
and therefore this example
as well as most applications
you're going to build with Docker,
will typically need cross container communication
and that will therefore be another form of communication
and of networking,
which we're going to take a closer look at
in this module.