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So now we know what Docker is

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and what containers are and why we might wanna use it.

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We will learn what exactly Kubernetes is a little bit later

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in the course, by the way.

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But let's stick at the basics for now.

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Containers and Docker.

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The problems solved by Docker

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and containers makes sense hopefully

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and it makes sense that we might be looking

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for a solution like Docker and containers

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but if you've been in the software development area

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for some time, you might also think to yourselves

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why Docker and why containers?

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Isn't that a problem?

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So that reproducible environment thing,

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isn't that a problem which we can solve

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with virtual machines?

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So machines running on our machines?

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Virtual machines with virtual operating systems encapsulated

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in their own shell independent

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from our host operating system,

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isn't that a solution?

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Well, kind of.

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With virtual machines,

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we have our host operating system,

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Windows or macOS or Linux

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and then on top of that, we install the virtual machine.

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So a computer inside of our computer so to say.

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This virtual machine has its own operating system,

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the virtual operating system,

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which runs inside of that virtual machine.

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Let's say Linux.

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Then in this virtual machine,

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since it is like a computer,

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it's just virtually emulated you could say,

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but inside of that virtual machine,

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we can then install extra tools.

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We can install whatever we want in there

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because it is just another machine,

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even though it just exists virtually.

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We can install all the libraries, dependencies

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and tools which we need

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and then also, move our source code there.

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And hence, since it's an encapsulated virtual machine

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with everything our program needs

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and all the tools being installed there,

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we kind of have the same result

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as with Docker and containers.

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We have an encapsulated environment

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where everything is locked in.

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And we could then have multiple such environments

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for different projects

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or we could share our virtual machine configuration

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with a colleague to ensure

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that we're working in the same environment.

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Well, this works but there are a couple of problems.

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One of the biggest problems is the virtual operating system

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and in general,

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the overhead we have with multiple virtual machines.

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Every virtual machine is really like a standalone computer,

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a standalone machine running on top of our machine.

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And therefore, if we have multiple such machines especially,

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we have a lot of wasted space and resources

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because every time a brand new computer has

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to be set up inside of our machine

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and that, of course, eats up memory, CPU

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and of course, also space on our hard drive.

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And that really can become a problem

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if you have more and more virtual machines on your system.

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Because if you have a lot of things,

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which are always the same

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and still duplicated, especially the operating system.

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You might be using Linux in all your virtual machines

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and still it's installed separately in every machine.

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And that, of course, wastes a lot of space.

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In addition, you might have a lot

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of other tools installed in every virtual machine,

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which your application doesn't need directly

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but which still are set up as a default.

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And that can be a problem.

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So to sum it up,

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virtual machines have a couple of pros and cons.

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They do allow us to create separated environments

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and we can have environment-specific configurations in them

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and we can share and reproduce everything reliably

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but we do have this redundant duplication,

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that wasted space.

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Performance can be bad

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since we have an extra machine running on top

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of our host system

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and especially if we have multiple such machines,

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performance can really degrade.

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And in addition, even though it is reproducible

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and sharable, that also can be tricky

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because if you still have to set up that virtual machine

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on every system where you want it

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and you have to then configure it in exactly the same way.

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There is no single config file you can necessarily share.

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If you wanna deploy your application,

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so from development to production,

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you also have to ensure

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that you configure your production machine

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in the same way as your virtual machine.

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Alternatively, you run your virtual machine

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on your production machine

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but that wasted performance,

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that's something you might not wanna do in production.

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So it solves the problem but not in a perfect way.

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And you might guess

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that's why we have Docker and containers.

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And actually, it's really important to understand

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that containers is the key concept here.

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Docker is just the defacto standard tool

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for creating and managing them.

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So why does Docker help us with that?

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How do containers solve that problem in a better way

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than virtual machines do?

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With containers, we still have our host operating system,

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Windows, macOS, Linux, whatever it is

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but then we don't install a couple of machines

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in the machine.

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Instead, we utilize built-in container support,

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which our operating system has

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or emulated container support,

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something Docker will take care about that this works.

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And then we run a tool called the Docker Engine

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on top of that.

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And that will all be set up by Docker

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when we install it, by the way.

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And then, based on that Docker Engine,

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which now runs on our system,

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which is just one tool,

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one lightweight small tool being installed there,

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we can spin up containers.

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And these containers contain our code

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and the crucial tools and runtimes our code needs,

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like Node.js, for example,

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but they don't container a bloated operating system,

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tons of extra tools or anything like that.

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They might have a small operating system layer

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inside of the container

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but even that will be a very lightweight version

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of an operating system,

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much smaller than anything you would install

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in a virtual machine.

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And you're going to see how containers work exactly

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and how you create them throughout this course, of course.

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Now, the other great thing about containers

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is that you can configure and describe them

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with a configuration file

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and you can then share that file with others

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so that they can recreate the container

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or you can also build the container into something,

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which is called an image,

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which you need to do anyways

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and then you can share that image

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with others to ensure that everyone's able

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to launch that same container which you have

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on your system on their systems.

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And obviously, we're going to dive in detail into images

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and containers throughout this course,

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so you are going to learn all about that step by step.

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So if we compare containers to virtual machines,

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we have a couple of advantages on the container side.

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They have a low impact on our operating system and machine.

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They've very fast.

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And they use minimal disk space,

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sharing, rebuilding and distributing them

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is very, very easy

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because we have these images

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and these configuration files.

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And we still have encapsulated apps and environments

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with everything our app needs but nothing more,

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which is perfect, which is exactly what we want.

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Virtual machines, on the other hand,

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have that bigger impact on your operating system.

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They tend to be slower

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and they also tend to eat up more of our disk space.

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In addition, as I said, sharing, rebuilding

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and distribution, that all can be done

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but also may be trickier than with containers and Dockers.

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Still, of course, we encapsulate our environments

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but we don't just encapsulate our app

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and what it needs to run but entire computers.

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It's like having a totally separate machine,

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which in rare examples, or in rare uses cases,

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could be an advantage but often,

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it's just a bloated thing, which you don't necessarily need.