How to Install and Use Docker Compose on Ubuntu

In this article, we will install Docker and Docker Compose and this guide will also help you to understand how Docker Compose works.

Prerequisites

To follow the steps we have mention in this article, you will need the following:

• Ubuntu 14.04 or later
• A non-root user with sudo privileges

Installing Docker

You will have to install Docker first if you haven't already. The easiet way to install Docker is to download and install their installation script (you'll be prompted for a sudo password).

wget -qO- https://get.docker.com/ | sh 

Working with Docker is a headache if your user is not configured correctly, so add your user to the docker group with the following command.

sudo usermod -aG docker $(whoami) 

Log out and log in from your server to activate your new groups.

Installing Docker Compose

Since you have Docker installed, let's move to the next step of installing Docker Compose. You need to install python-pip as prerequisite:

sudo apt-get -y install python-pip 

Then you can install Docker Compose:

sudo pip install docker-compose 

Running a Container with Docker Compose

The public Docker registry, Docker Hub, includes a simple Hello World image. Now that we have Docker Compose installed, let's test it with this really simple example.

Create a directory for our YAML file:

mkdir hello-world 

Then change into the directory:

cd hello-world 

Now create the YAML file using your favorite text editor (we will use nano):

nano docker-compose.yml 

Put the following contents into the file, save the file, and exit the text editor:

my-test:
  image: hello-world

The first line will be used as part of the container name. The second line specifies which image to use to create the container. The image will be downloaded from the official Docker Hub repository.

While still in the ~/hello-world directory, execute the following command to create the container:

docker-compose up 

The output should start with the following:

Output of docker-compose up

Creating helloworld_my-test_1...
Attaching to helloworld_my-test_1
my-test_1 | 
my-test_1 | Hello from Docker.
my-test_1 | This message shows that your installation appears to be working correctly.
my-test_1 | 

The output then explains what Docker is doing:

1. The Docker client contacted the Docker daemon.
2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
3. The Docker daemon created a new container from that image which runs the executable that produces the output you are currently reading.
4. The Docker daemon streamed that output to the Docker client, which sent it to your terminal.

If the process doesn't exit on its own, press CTRL-C.

 

Learning Docker Compose Commands

Let's go over the commands the docker-compose tool supports.

docker-compose up -d 

docker-compose will now fork to the background.

To show your group of Docker containers (both stopped and currently running), use the following command:

docker-compose ps 

For example, the following shows that the helloworld_my-test_1 container is stopped:

Output of `docker-compose ps`

Name           Command   State    Ports 
-----------------------------------------------
helloworld_my-test_1   /hello    Exit 0         

A running container will show the Up state:

Output of `docker-compose ps`

Name              Command          State        Ports      
---------------------------------------------------------------
nginx_nginx_1   nginx -g daemon off;   Up      443/tcp, 80/tcp 

To stop all running Docker containers for an application group, issue the following command in the same directory as the docker-compose.yml file used to start the Docker group:

docker-compose stop 

Note:docker-compose kill is also available if you need to shut things down more forcefully.

In some cases, Docker containers will store their old information in an internal volume. If you want to start from scratch you can use the rm command to fully delete all the containers that make up your container group:

docker-compose rm  

If you try any of these commands from a directory other than the directory that contains a Docker container and .yml file, it will complain and not show you your containers:

Accessing the Docker Container Filesystem

If you need to work on the command prompt inside a container, you can use the docker exec command.
Create a new directory for it and change into it:

mkdir ~/nginx && cd $_ 

Create a docker-compose.yml file in our new directory:

nano docker-compose.yml 

and paste in the following:

nginx:
  image: nginx

Save the file and exit. We just need to start the Nginx container as a background process with the following command:

docker-compose up -d 

The Nginx image will be downloaded and then the container will be started in the background.

Now we need the CONTAINER ID for the container. List of all the containers that are running:

docker ps 

You will see something similar to the following:


If we wanted to make a change to the filesystem inside this container, we'd take its ID (in this example e90e12f70418) and use docker exec to start a shell inside the container:

docker exec -it e90e12f70418 /bin/bash 

The -t option opens up a terminal, and the -i option makes it interactive. The /bin/bash options opens a bash shell to the running container. Be sure to use the ID for your container.

You will see a bash prompt for the container similar to:

root@e90e12f70418:/#

From here, you can work from the command prompt. Keep in mind, however, that unless you are in a directory that is saved as part of a data volume, your changes will disappear as soon as the container is restarted. Another caveat is that most Docker images are created with very minimal Linux installs, so some of the command line utilities and tools you are used to may not be present.

 

Conclusion