depending on where you are in the world.

This is CS50 on Twitch.

My name is Colton Ogden and I'm joined today by--

DAVID MALAN: David Malan, also of CS50.

Good to see everyone again.

It's been a while.

COLTON OGDEN: Yeah, it's been a while.

When was the last stream that you were on, do you remember?

DAVID MALAN: Oh, it was good December.

I think we've played Zelda last time.

COLTON OGDEN: Oh, that's true.

It was not as much of an educational stream as today.

DAVID MALAN: It was very educational.

COLTON OGDEN: We could say a little bit of game development stuff.

DAVID MALAN: What game are we here to play today?

I'm all set to accrue some points.

COLTON OGDEN: It's a game called Docker.

I believe it stars a whale of some kind and some boxes on top of them.

DAVID MALAN: Indeed.

COLTON OGDEN: We have a bunch of people that are in the chat already.

DAVID MALAN: I see.

A lot of people have tuned in already.

Nice to see some familiar names.

COLTON OGDEN: We're almost at the magic number of 50.

We have 49 viewers currently.

DAVID MALAN: Oh, and what happens after 50?

COLTON OGDEN: Then we just get tons of-- just tons of money,

just showered with money.

Yeah, we have a lot of people in the chat.

There's a lot of regulars.

I shouted out a bunch of people in the chat,

but thanks so much for everybody who's joining.

Dan Nurell, Bavick Night, we have Belicures, Elias, Assly, Brenda,

Mr. Frigg--

who I think is a new person.

Kugie Snipers, We Be, ISO TV.

I think ISO TV was one of the first people.

DAVID MALAN: I'm impressed you can pronounce all these so easily.

COLTON OGDEN: I've gotten a lot of practice at this point.

M. Kloppenburg, thanks for joining-- another regular.

For Sunlight, Suraton, GP Guy.

We have an absolute ton of people.

DAVID MALAN: Oh, we've got a first-timer here.

1Jacko0TS.

I don't know.

COLTON OGDEN: Oh, yeah, 1JackOTS.

Thanks so much for the follow layout.

They followed right before this stream as well.

DAVID MALAN: Nice.

Hello, Elasorsa.

COLTON OGDEN: Elasorsa, yeah, that's a new person as well,

and Adamantine Bipartite.

What's up, David and Colton?

What's up?

That's the first I've seen that name.

That's a long name.

DAVID MALAN: Yeah, we've got a lot.

Nice to see everyone here.

COLTON OGDEN: Yeah, Amed Osman, and--

DAVID MALAN: Another first-timer from Adam.

COLTON OGDEN: Yeah, M. Gonayni says hello.

WhipStreak23, there we go, another regular.

DAVID MALAN: 52.

Oh, we missed the 50.

We blinked and it was gone.

COLTON OGDEN: We did, yeah.

So what are we--

what exactly is Docker?

That's what we-- we sort of spoiled what we're talking about today.

It's not actually a game.

DAVID MALAN: No, I'm sorry.

So tune out now if you don't want to learn something really interesting,

though technically.

So Docker is containerization.

COLTON OGDEN: Oh, wait.

It looks like your laptop is not--

DAVID MALAN: Oh, we're not plugged in.

Oh, user error, apologies.

COLTON OGDEN: Sorry.

Sorry, that's my fault. I should have--

DAVID MALAN: And if Colton is going to tell some jokes here for just a moment.

COLTON OGDEN: Oh, man.

I didn't have any.

DAVID MALAN: Did you hear about the guy who--

I don't know.

COLTON OGDEN: Who forgot to plug-in his dongle?

DAVID MALAN: Yeah.

Here we go.

Let me go ahead and--

today's lesson will be about how to change your display preferences.

Here we are going under Scaled so as to do 720p,

which isn't actually a very high resolution,

but for our purposes of streaming technical content,

makes it all a lot more readable on the screen.

COLTON OGDEN: Oh, look, Brian's actually on the chat.

He says hello--

BrianU28.

DAVID MALAN: Oh, nice.

Please send all of your questions to Brian U, who is here from CS50's team.

COLTON OGDEN: Yeah, Brian I'm sure knows a lot about Docker too.

DAVID MALAN: So let's begin.

Again, so Docker is containerization technology.

But what does that actually mean?

Well, let's rewind a little bit.

Normally when you're running software it's

on your Mac, or your PC, or your server, or somewhere else,

and you have installed whatever operating system was installed when you

bought it or when you first set it up--

Mac OS, Windows, Linux, or whatnot.

The problem, though, arises in a server side environment

where you want to run multiple applications.

Like CS50 has a whole suite of web apps.

We have the CS50 Sandbox, CS50 Lab, if you started tuning in to CS50X 2019.

We have help50, and style50, and bunches more.

So all of these apps have their own dependencies, like certain software,

and libraries, and frameworks that they need.

And frankly, not all apps need the same things.

And so in yester year, only five plus years ago, we, CS50,

used to have a centralized architecture for all of our web apps.

We had what were called vhost servers, virtual hosting servers

running popular web server software called Apache.

And what we would do is we pretty much had

to find the greatest common denominator among all of our apps

and actually install on those servers every library

and every piece of software that every app might possibly need.

The problem, of course, is that eventually you

run into incompatibilities.

One needs this version, another needs that, and now you're just out of luck.

And if something breaks in one app, it's not isolated from another,

and so one app can take down the rest.

So Docker ultimately is about isolating your applications from one another.

COLTON OGDEN: And so it says on your web page there, what is a container?

I'm guessing that the whale and the boxes on top of the whale

are like a representation of this idea of containers?

DAVID MALAN: Indeed.

We can pull this up if I enhance this image up here.

So Docker is a company that also makes and contributes

to open source software, which is also called Docker.

And indeed, you can see those little boxes represent those big--

we call them containers.

That really big--

COLTON OGDEN: Shipping containers.

DAVID MALAN: Shipping containers that tractor trailer trucks generally

cart around.

So it's actually pretty cute.

The whale is instead the ship and it's holding up the containers,

and it's really cute.

If you want to go ahead today even, install Docker, at least on Mac OS,

the first message that the software will print for you is,

"We are whaley glad to see you."

COLTON OGDEN: Wow, that's cringey.

DAVID MALAN: A little bit, a little hard to say.

But I should say, some folks out there might be familiar perhaps

with virtualization software.

For instance, has anyone used VMware, or Parallels, or other such tools?

Those are--

COLTON OGDEN: That's certainly been around for a while, a long--

DAVID MALAN: A long time.

COLTON OGDEN: Much longer than Docker has.

And I know I've definitely used it quite a bit.

DAVID MALAN: Yeah, and we use those too.

But with virtualization software, or virtual machines,

or virtual machine monitors-- bunch of different ways to describe essentially

the same thing--

you would have to run, you could run, multiple operating systems

on your same computer.

Essentially, each OS in its own window.

The problem with a VM or virtual machine is

it virtualizes the entire hardware-- the CPU, and the memory, and the disk,

and the files, and everything.

So it actually is a lot heavier weight.

You have a lot of redundancy.

If you have Linux in your virtual machines,

you have as many copies of Linux running and installed

as you have virtual machines.

COLTON OGDEN: So a Docker-- part of what Docker does is sort of mitigates

that resource use on your machine?

DAVID MALAN: Indeed.

So I pulled this up in advance, one, to learn what Docker is, and two,

to actually show some of the fun pictures that they have.

That actually does paint a nice picture here.

I think if we scroll down--

yeah, indeed.

So here on the right--

this is just on Docker/resources/what-container.

On the right, you see an artist's rendition of what a virtual machine is.

At the lowest level you have your hardware, your infrastructure,

like the physical servers.

The blue bar above that is the hypervisor, a.k.a.

virtual machine monitor, a.k.a.

VMware, or Parallels, or other software too.

And then on top of that conceptually you have maybe Windows installed,

and Linux installed, and maybe Mac OS-- but Apple does not make that easy--

otherwise known as your "guest operating systems."

And on those guest operating systems, you

have your individual apps each running.

So now if you look to the left, what seems to be missing, for instance?

COLTON OGDEN: Well, there's no virtual machines separating the apps.

They're all running in sort of the same bucket, which

is the container as applications arrow.

That's what that's referring to?

DAVID MALAN: Yeah, exactly.

Yeah, each of those apps is a containerized application,

which means each app is using Docker.

Docker is now the software beneath them that makes all this possible.

And notice, you only have one operating system.

So you run, for instance, Linux or something

on your own based computer, and thanks to Docker,

can you now share just one other operating system,

if you'd like, across all of those applications.

And moreover and most excitingly, if all of those apps--

A, B, C, D, E, F-- are all running Ubuntu Linux Version 18, well, then

what you'll have is one base installation of Ubuntu.

And if app A and B need slightly different software,

they're just going to be layered on top.

Docker supports what's called a "union file system."

So if we both have apps that we've written

using Linux but I need a library called Foo and you need Bar,

we'll share the same base layer.

But for you, Docker will layer Bar on it,

but for me, Docker will layer Foo on it, but still have that commonality

underneath.

COLTON OGDEN: And if we both need two different versions of Ubuntu,

does it do similar types of things?

DAVID MALAN: It does.

You go a little lower level, but then each of us has our own copy of Ubuntu--

15, or 16, or 18, or whatnot--

and then, yes, those are isolated from each.

COLTON OGDEN: Pretty cool.

Yes, so it sounds like in factors out a lot of the bulk, the unnecessary bulk

associated with running multiple VMs.

DAVID MALAN: Indeed.

COLTON OGDEN: I know we definitely have a bunch of messages here.

DAVID MALAN: Well, let's catch up on these.

COLTON OGDEN: Some people have definitely talked about Apache in hear.

And people are asking, "What is Docker?

I wear Dockers."

They think it's a clothing brand.

I'm trying to do this in code recover--

55 people.

DAVID MALAN: There we go.

This is what we'll be talking about today.