docker_basics.md

Docker basics

Enough of theory. It's time to explore what docker can actually do.

Docker client

Docker ships with a client which is used to put stuff in a container, load containers in ships, remove containers from ships and so on.

It's how we interact with images and containers, actually a little more than that.

Hands-on

Available commands

To check the available commands within the docker binary you can type either:

docker -h

OR

docker

This is how you are going to search for help.

Summary

We learned how to search for help using the documentation available within the docker binary.

Example 1: Hello world

The guys from docker built a hello world image to test our docker installation and understand the basics of it.

Type this in the terminal:

docker run hello-world

You'll see that docker downloaded an image, built a container based on that image and then ran it.

To see the downloaded image you can type:

docker images

If you didn't see the part of building a container based on the image, it's fine. We still can check if it's true doing:

docker ps

Hummm. Got nothing? Try with -a option from ALL (running and stopped containers):

docker ps -a

Now, you see it.

So, if the container is still running it's possible to see it with just the ps without the option "-a", but if the container is stopped we have to include the "-a" option. Or, you can do it like me run the command with the "-a" option all the time.

If you are like me, there is still a question to ask. Where the hello world image is stored?

Well, docker offers us a hub to store the images. The hub can be found on the address https://hub.docker.com. Also, there is a cloud service, you can get more information on the link https://cloud.docker.com.

The image can be found on this address.

Summary

We learned how to run a container, show a list of downloaded images and containers.

Questions

1. Which docker command we use to run a container?

• [A] ps
• [B] exec
• [C] run
• [D] container

2. Which docker command we use to list images downloaded?

• [A] img
• [B] image
• [C] list
• [D] images

3. Which docker command we use to list containers?

• [A] c
• [B] ps
• [C] container
• [D] containers

Example 2: Pulling images

To download images previously before running them, you can use the command below:

docker pull docker/whalesay

Now, try to run this image with the parameters below to see if docker will download it again:

docker run docker/whalesay cowsay <YOUR_NAME>

As you can see, no images were downloaded and you also got a whale saying your name as a gift.

Summary

We learned how to download an image from the docker hub.

Questions

1. Which docker command we use to download an image?

• [A] down
• [B] pull
• [C] push
• [D] download

Example 3: Static site

I've created an image to show a clean and simple static website. While you are running this image, I'll show you some of the other docker commands. First, let's get the image.

Hummm. I can't remember it's name, just a sec let me look at my notes... I can't find it.

Well, we can try to search for my docker hub username to see if we can find it.

docker search carlancalazans

There it is! Let's run it.

docker run carlancalazans/static_site

Well, it's running. Running a container this way isn't good because we have a blocked terminal, we can't type any other command.

To fix this, hit CTRL+C and add the -d option on the command line:

docker run -d -P carlancalazans/static_site

This new option will run the container in background mode (detached). Now, we can execute some more commands. I added another option -P to publish all exposed ports.

To get basic information from container, type:

docker ps

If you look at the name and think this is automatically generated. You are right!

Sometimes it's hard to remember the container name or reference it as the id, so let's rename it.

docker rename <ID OR NAME> static_site
docker ps

Much better. To get information like how much memory and cpu usage, type:

docker stats static_site

To get some more information about the container formatted in json, type:

docker inspect static_site

Are you curious about what I'm using to serve the static website? Try to guess the answer for less than 5 seconds.

Are you ready to find the truth? Type the command below:

docker top static_site

Did you get it right?

This command will show us an output of the running processes inside the container. It's very similar to the command top from Linux. As a matter of fact, just type it on the terminal.

top

As you can see, this is a list of all processes running on this virtual machine. Hit q to exit.

Until now, we didn't even had a chance to access the website. For this, we need to get the running port from the webserver. To see all the ports mapped to this container, type:

docker port static_site

Now, you can map a port on your virtual machine to access the website. I'll show you how to do this in person, it's not complicated. We will forward a port from the VM to our machine.

As you can see, it's just a html page, super simple.

I wanna see some logs from the webserver, how about you? Yeah?

To get the logs from a container, execute the below in a terminal:

docker logs static_site

Well, that's the end of this sample.

We are leaving some containers and images behind. Let's clean all up before finish.

To kill the process of a running container, just type:

docker kill static_site
docker ps

Nice! We also have other commands like restart, stop, start, pause and unpause. The container isn't running anymore, to remove it do this:

docker rm static_site
docker ps -a

Good! We don't have any container, let's delete the image with:

docker rmi carlancalazans/static_site
docker images -a

Very good. I'll talk to you again on the next example.

Summary

We learned a few things from this sample.

1. How to search for images
2. How to run containers in detached mode and also how to expose ports
3. How to rename containers
4. How to get statistics from containers
5. How to inspect a container formatted in json
6. How to get a list of running processes inside of a container
7. How to get a list of mapped ports between the container and our own machine
8. How to see the logs from a container
9. How to kill/stop a container
10. How to remove a container
11. How to remove images

Questions

1. Which docker command we use to search for images?

• [A] s
• [B] get
• [C] list
• [D] search

2. Which option we use to run a container in detached mode?

• [A] b
• [B] d
• [C] a
• [D] c

3. Which docker command we use to rename a container?

• [A] rn
• [B] rename
• [C] r
• [D] ren

4. Which docker command we use to get statistics of a container?

• [A] stats
• [B] get
• [C] stat
• [D] st

5. Which docker command we use to get more information about a container formatted in json?

• [A] get
• [B] retriv
• [C] inspect
• [D] view

6. Which docker command we use to get the information of running processes in a container?

• [A] ps
• [B] proc
• [C] top
• [D] list

7. Which docker command we use to get a list of exposed ports on a container?

• [A] port
• [B] p
• [C] ports
• [D] get

8. Which docker command we use to see the logs of a container?

• [A] log
• [B] l
• [C] view
• [D] logs

9. Which docker command we use to kill a container?

• [A] kill
• [B] k
• [C] stop
• [D] term

10. Which docker command we use to remove a container?

• [A] remove
• [B] del
• [C] rm
• [D] stop

11. Which docker command we use to remove an image?

• [A] rm
• [B] remove
• [C] rmi
• [D] delete

Example 4: Quotes

I created a very simple Python project, which will server as our sample on this section.

The intent of the application is to show some quotes in the middle of the screen. When we hit CTRL+R or F5, the quote will be refreshed.

First, let's run to see it working:

docker run -d -p 4000:4000 carlancalazans/quotes

Have you noticed something new here?

Instead of using the option -P (capitalised) I'm using -p (lowercase) to map a port on my machine to the container. First is the port on our machines and later is the port of the container. I've setup the application to run on port 4000.

With the container running, open a tab on the browser and go to the url http://localhost:4000. As you can see, if it's all working, it does exactly what I told you before.

How to add more quotes or how to change the quotes presented? In the case you didn't like them. It's totally fine, no worries.

Well, I don't have an administration page or a page where you can insert/update/delete quotes. The quotes are in a text file quotes.txt inside a folder called database on the directory /usr/src/app. The application will load this file when it's starting and than manage the contents in memory. As I said, super simple.

So, how we are going to change this file?

To do this, we will need to setup a volume, but what is a volume? You can ask.

A data volume is a special directory that we can use to share data with one or more containers. You can think of it like a usb drive, if it's plugged in you can have access to it, read and write files. On the other hand, if it's not you can't access the data. You can create persistent volumes, but for the sake of this sample we will create just a bind-mounted one to see it working.

On this sample we are going to modify the quotes.txt stored inside the image to show anything you want, you can have your own version of the quotes.txt stored in some directory and by using a volume you can serve it.

To do this, we need to learn how to set a volume. It's so simple that maybe you already know. Let's see.

docker run -d -v <PATH_MY_DIR>:/usr/src/app/database -p 4000:4000 carlancalazans/quotes

It's important to note that you'll need the complete path of your local directory. For us, will be something like /home/docker/quotes/database/quotes.txt and than we can specify the mount point inside the image.

With the container running you can access the mapped port on your machine to see the results. I hope you can see your quotes or whatever you wrote on the quotes.txt file on the screen.

Summary

We learned how to map a port on our machines to a container port. Also, how create volumes to share data with a container.

Questions

1. Which option we use to map a port between our machine and a container?

• [A] p
• [B] P
• [C] port
• [D] ports

2. Which option we use to map a directory between our machine and a container?

• [A] m
• [B] map
• [C] v
• [D] dir