Install Docker

Overview

In this step, we are going to install Docker. This is one of the steps that will actually not be performed inside of the container image. But, of course, we need Docker on the host in order to run containers.

Install Docker

We now have an updated Ubuntu operating system. We are ready to install Docker.

1. We need to add the GPG key for the official Docker repository to the system because in the next step we want to download the Docker 'installer' directly from Docker and not the default Ubuntu servers to ensure we get the latest version of the engine. From the command prompt, type the following:

sudo apt-key adv --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys 58118E89F3A912897C070ADBF76221572C52609D

2. Now, we need to tell Ubuntu where the Docker repository is located. From the command prompt, type (or paste) the following:

sudo apt-add-repository 'deb https://apt.dockerproject.org/repo ubuntu-xenial main'

3. Once again, update the package database with the Docker packages from the newly added repository:

sudo apt-get update

4. Make sure you are about to install from the Docker repository instead of the default Ubuntu repository:

apt-cache policy docker-engine

5. You should see output similar to the following (notice that docker-engine is not installed and the docker-engine version number might be different):

docker-engine:
Installed: (none)
Candidate: 1.11.1-0~xenial
Version table:
   1.11.1-0~xenial 500
      500 https://apt.dockerproject.org/repo ubuntu-xenial/main amd64 Packages
   1.11.0-0~xenial 500
      500 https://apt.dockerproject.org/repo ubuntu-xenial/main amd64 Packages

6. Finally, install Docker:

sudo apt-get install -y docker-engine

7. Installing the Docker engine may take an additional minute or two.

Additional Configuration

To simplify running and managing Docker, there's some additional configuration that we need to implement. While this section is optional, it is recommended to make managing Docker much easier.

Ensure Docker Engine is Running

1. From the command prompt, type:

sudo systemctl status docker

2. You should see something similar to the following:

● docker.service - Docker Application Container Engine
   Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
   Active: active (running) since Sun 2017-06-04 22:38:16 UTC; 4min 10s ago
     Docs: https://docs.docker.com
 Main PID: 32844 (dockerd)

3. Because the service is running, we can now use the docker command later in this workshop.

Enable Docker Engine at Startup

Let's make sure the Docker engine is configured to run on system startup (and reboot).

1. From the command prompt, type:

sudo systemctl enable docker

2. You should see something similar to the following:

Synchronizing state of docker.service with SysV init with /lib/systemd/systemd-sysv-install...
Executing /lib/systemd/systemd-sysv-install enable docker

Elevate Your Privileges

Be default, running the docker command requires root privileges - that is, you have to prefix the command with sudo. It can also be run by a user in the docker group, which is automatically created during the install of Docker. If you attempt to run the docker command without prefixing it with sudo or without being in the docker group, you'll get an output like the following:

docker: Cannot connect to the Docker daemon. Is the docker daemon running on this host?.
See 'docker run --help'.

To avoid typing sudo whenever you run the docker command, add your username to the docker group:

sudo usermod -aG docker $(whoami)

You will then need to log out and back in for the changes to take effect.

If you need to add another user to the docker group (one in which you have not logged in as currently), simply provide that username explicitly in the command:

sudo usermod -aG docker <username>

You've successfully installed the Docker engine. You have also configured it to run at startup and have added yourself to the Docker group so that you have sufficient privileges for running Docker.