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[Intro Music]

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In each new programming language

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learner will always start with

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simple program called hello-world.

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And the studying of Docker is not

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an exception. That's why I suggest

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to start from the very first simple

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container, the most simple one,

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called hello-world. For now, you

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should have Docker installed on

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your computer, and we are basically

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ready to go. Let's go to terminal,

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I'll use macOS in this section,

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and the let me simply type 'docker

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run hello-world', like this, press

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Enter, and see what will happen. I

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see message, 'Unable to find image

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'hello-world:latest' locally'.

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After that image is pulled from

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Docker Hub. And afterwards, I see

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this section of text in terminal -

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Hello from Docker! This message

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shows that installation appears to

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be working correctly, and so on.

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Afterwards, I got back to terminal

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and actually you see that container

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was exited. You could also verify

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that there are no currently running

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containers using command 'docker ps'.

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And you see here empty output only

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with headers of the columns like

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CONTAINER ID, IMAGE, COMMAND, and so

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on. Let's try to run the same

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container once again. 'docker run

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hello-world', Enter, and now

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you'll see the same result as

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before. The goal of this container

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is simply to start and print this

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piece of text to terminal. Nothing

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else. As soon as this is done,

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container exits. That's all about

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the most simple hello-world

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container that you could use in

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Docker. And also from this example,

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you see that Docker has actually

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pulled the image called hello-world

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:latest' from Docker Hub. You

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see this action here. This image

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also has sha256 Hash. And here you

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see this hash as well. Great.

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That's how you're able to create

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the very first container pretty

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fast and easily. But basically this

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container is useless. All what it

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does, it simply prints to the

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console a piece of text, and that's

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it. Also, let's have a look at the

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this sequence of actions that

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actually happened under the hood

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when we have entered this command

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'docker run hello-world'. First step,

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Docker client contacted the Docker

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daemon. It means that there are two

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different pieces of software -

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Docker client on one side, and

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Docker daemon or Docker server on

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the other side. Next, Docker daemon

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pulled the "hello-world" image from

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the Docker Hub. That's what I have

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already told you. We have tried to

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find the image called 'hello-world

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:latest' locally, but there

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were no images, there was just

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clean installation and that's it.

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That's why Docker server or Docker

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daemon has decided to pull image

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'hello-world' from a Remote Registry

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called Docker Hub. Here you see

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this information. On the next step,

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step number 3, Docker daemon

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created a new container from that

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image which runs executable that

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produces output you are currently

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reading. It means that after pulling

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the image from Remote Registry, from

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Docker Hub, local Docker has

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created a new container based on

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that image. On the last step,

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Docker daemon streamed that output

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to the Docker client. And that's why

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you actually see this text here in

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your terminal. And afterwards, the

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Docker container was basically

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terminated. Actually, I would add

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here additional step, step number

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5, container was exited. That's

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actually all what happened under

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the hood when you have entered

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this command 'docker run hello-

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world'. When you run the same

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command, second time, third time

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and so on, Docker skips this step,

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because this image 'hello-world' is

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already present in your local

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cache, and you could verify that

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using command 'docker images', and

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you'll see first image here on

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the list, 'hello-world', and there was

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a tag called 'latest'. We will get

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back to tags a bit later in this

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course. Also, you may see here

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IMAGE ID. It is simply a set of

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characters, hexadecimal characters,

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basically. And you'll see how long

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ago this image was created. It was

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created more than one year ago, and

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its size is simply two kilobytes.

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It is the most smallest image

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possible. Okay, that's all for this

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example, and let's move on to next one.

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[no audio]