container.training/slides/intro/First_Containers.md

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Our first containers

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Objectives

At the end of this lesson, you will have:

• Seen Docker in action.

• Started your first containers.

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Hello World

In your Docker environment, just run the following command:

$ docker run busybox echo hello world
hello world

(If your Docker install is brand new, you will also see a few extra lines, corresponding to the download of the busybox image.)

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That was our first container!

• We used one of the smallest, simplest images available: busybox.

• busybox is typically used in embedded systems (phones, routers...)

• We ran a single process and echo'ed hello world.

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A more useful container

Let's run a more exciting container:

$ docker run -it ubuntu
root@04c0bb0a6c07:/#

• This is a brand new container.

• It runs a bare-bones, no-frills ubuntu system.

• -it is shorthand for -i -t.

  • -i tells Docker to connect us to the container's stdin.

  • -t tells Docker that we want a pseudo-terminal.

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Do something in our container

Try to run figlet in our container.

root@04c0bb0a6c07:/# figlet hello
bash: figlet: command not found

Alright, we need to install it.

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Install a package in our container

We want figlet, so let's install it:

root@04c0bb0a6c07:/# apt-get update
...
Fetched 1514 kB in 14s (103 kB/s)
Reading package lists... Done
root@04c0bb0a6c07:/# apt-get install figlet
Reading package lists... Done
...

One minute later, figlet is installed!

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Try to run our freshly installed program

The figlet program takes a message as parameter.

root@04c0bb0a6c07:/# figlet hello
 _          _ _       
| |__   ___| | | ___  
| '_ \ / _ \ | |/ _ \ 
| | | |  __/ | | (_) |
|_| |_|\___|_|_|\___/ 

Beautiful! .emoji[😍]

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Counting packages in the container

Let's check how many packages are installed there.

root@04c0bb0a6c07:/# dpkg -l | wc -l
190

• dpkg -l lists the packages installed in our container

• wc -l counts them

How many packages do we have on our host?

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Counting packages on the host

Exit the container by logging out of the shell, like you would usually do.

(E.g. with ^D or exit)

root@04c0bb0a6c07:/# exit

Now, try to:

• run dpkg -l | wc -l. How many packages are installed?

• run figlet. Does that work?

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Host and containers are independent things

• We ran an ubuntu container on an ubuntu host.

• But they have different, independent packages.

• Installing something on the host doesn't expose it to the container.

• And vice-versa.

• We can run any container on any host.

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Where's our container?

• Our container is now in a stopped state.

• It still exists on disk, but all compute resources have been freed up.

• We will see later how to get back to that container.

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Starting another container

What if we start a new container, and try to run figlet again?

$ docker run -it ubuntu
root@b13c164401fb:/# figlet
bash: figlet: command not found

• We started a brand new container.

• The basic Ubuntu image was used, and figlet is not here.

• We will see in the next chapters how to bake a custom image with figlet.