Getting Started with Docker

Getting started with Docker:

1. First Container

root@master1:~# docker run busybox echo hello world
hello world

What we did?
. 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

2. Let's explore further more:

root@master1:~# docker run -it ubuntu
root@91fa3b4e1048:/#

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

3. Let's try installing figlet inside this container

Try to run figlet in our container.
root@04c0bb0a6c07:/# figlet hello
bash: figlet: command not found
Alright, we need to install it.

Let's check how many packages are installed here.
root@04c0bb0a6c07:/# dpkg -l | wc -l
189
• dpkg -l lists the packages installed in our container
• wc -l counts them
• If you have a Debian or Ubuntu machine, you can run the same command and
compare the results.

4. Installing Package inside the 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

One minute later, figlet is installed!
# figlet hello
_ _ _
| |__ ___| | | ___
| '_ \ / _ \ | |/ _ \
| | | | __/ | | (_) |
|_| |_|\___|_|_|\___/

5. How do we exit the shell in the container?

Just exit the shell, like you would usually do.
(E.g. with ^D or exit)
root@04c0bb0a6c07:/# exit

• Our container is now in a stopped state.
• It still exists on disk, but all compute resources have been freed up.
Reading package lists... Done

6. 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.

7. Our first containers were interactive.

We will now see how to:

• Run a non-interactive container.
• Run a container in the background.
• List running containers.
• Check the logs of a container.
• Stop a container.
• List stopped containers.
• We will see in the next chapters how to bake a custom image with figlet.

8. This container just displays the time every second.

$ docker run jpetazzo/clock
Fri Feb 20 00:28:53 UTC 2015
Fri Feb 20 00:28:54 UTC 2015
Fri Feb 20 00:28:55 UTC 2015
...
• This container will run forever.
• To stop it, press ^C.
• Docker has automatically downloaded the image jpetazzo/clock.
• This image is a user image, created by jpetazzo.
• We will hear more about user images (and other types of images) later.


9. Run a container in the background

Containers can be started in the background, with the -d flag (daemon mode):
$ docker run -d jpetazzo/clock
47d677dcfba4277c6cc68fcaa51f932b544cab1a187c853b7d0caf4e8debe5ad
• We don't see the output of the container.
• But don't worry: Docker collects that output and logs it!
• Docker gives us the ID of the container.

10.List running containers

How can we check that our container is still running?
With docker ps, just like the UNIX ps command, lists running processes.

$ docker ps
CONTAINER ID IMAGE ... CREATED STATUS ...
47d677dcfba4 jpetazzo/clock ... 2 minutes ago Up 2 minutes ...
Docker tells us:
• The (truncated) ID of our container.
• The image used to start the container.
• That our container has been running (Up) for a couple of minutes.
• Other information (COMMAND, PORTS, NAMES) that we will explain later

11.Starting more containers

Let's start two more containers.

$ docker run -d jpetazzo/clock
57ad9bdfc06bb4407c47220cf59ce21585dce9a1298d7a67488359aeaea8ae2a

$ docker run -d jpetazzo/clock
068cc994ffd0190bbe025ba74e4c0771a5d8f14734af772ddee8dc1aaf20567d

Check that docker ps correctly reports all 3 containers.

12.Two useful flags for docker ps

To see only the last container that was started:
$ docker ps -l
CONTAINER ID IMAGE ... CREATED STATUS ...
068cc994ffd0 jpetazzo/clock ... 2 minutes ago Up 2 minutes ...
To see only the ID of containers:

$ docker ps -q
068cc994ffd0
57ad9bdfc06b
47d677dcfba4

Combine those flags to see only the ID of the last container started!
$ docker ps -lq
068cc994ffd0

13.View the logs of a container

We told you that Docker was logging the container output.
Let's see that now.
$ docker logs 068
Fri Feb 20 00:39:52 UTC 2015
Fri Feb 20 00:39:53 UTC 2015
...
• We specified a prefix of the full container ID.
• You can, of course, specify the full ID.
• The logs command will output the entire logs of the container.
(Sometimes, that will be too much. Let's see how to address that.)

14.View only the tail of the logs

To avoid being spammed with eleventy pages of output, we can use the --tail
option:

$ docker logs --tail 3 068
Fri Feb 20 00:55:35 UTC 2015
Fri Feb 20 00:55:36 UTC 2015
Fri Feb 20 00:55:37 UTC 2015
• The parameter is the number of lines that we want to see.

15.Follow the logs in real time

Just like with the standard UNIX command tail -f, we can follow the logs of our
container:

$ docker logs --tail 1 --follow 068
Fri Feb 20 00:57:12 UTC 2015
Fri Feb 20 00:57:13 UTC 2015
^C
• This will display the last line in the log file.
• Then, it will continue to display the logs in real time.
• Use ^C to exit.

16. Stop our container

There are two ways we can terminate our detached container.
• Killing it using the docker kill command.
• Stopping it using the docker stop command.
The first one stops the container immediately, by using the KILL signal.
The second one is more graceful. It sends a TERM signal, and after 10 seconds, if the
container has not stopped, it sends KILL.
Reminder: the KILL signal cannot be intercepted, and will forcibly terminate the
container.
Background Containers
Docker