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Use Ansible to Install & Set Up Docker

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With the popularization of containerized applications and microservices, server automation now plays an essential role in systems administration. It is also a way to establish standard procedures for new servers and reduce human error.

This post explains how to use Ansible to automate the steps to set up docker. Docker is an application that simplifies the process of managing containers, resource-isolated processes that behave in a similar way to virtual machines, but are more portable, more resource-friendly, and depend more heavily on the host operating system.

While you can complete this setup manually, using a configuration management tool like Ansible to automate the process will save you time and establish standard procedures that can be repeated through tens to hundreds of nodes. Ansible offers a simple architecture that doesn’t require special software to be installed on nodes, and it provides a robust set of features and built-in modules which facilitate writing automation scripts.


Condition Check

In order to execute the automated setup provided by the playbook discussed in this guide, you’ll need:

  • Ansible installed either on your local machine or on a remote server that you have set up as an Ansible Control Node. You can follow Step 1 of the post How to Install and Configure Ansible on Ubuntu 18.04 to get this set up.

    • If you plan to use a remote server as your Ansible Control Node, it should have a non-root user with sudo privileges and a basic firewall configured prior to installing Ansible. Follow our Initial Server Setup Guide for Ubuntu 18.04 to set this up.

  • Access to one or more Ubuntu 18.04 servers which will be used as your Ansible hosts. Each should have a non-root user with sudo privileges and a basic firewall configured. Follow our guide on Automating Initial Server Setup with Ansible on Ubuntu 18.04 to set this up automatically. Alternatively, you can set this up manually by following our Initial Server Setup Guide for Ubuntu 18.04 on each of your Ansible hosts.


Testing Connectivity to Nodes

To make sure Ansible is able to execute commands on your nodes, run the following command from your Ansible Control Node:

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ansible -m ping all

This command will use Ansible’s built-in ping module to run a connectivity test on all nodes from your default inventory file, connecting as the current system user. The ping module will test whether:

  • your Ansible hosts are accessible;

  • your Ansible Control Node has valid SSH credentials;

  • your hosts are able to run Ansible modules using Python.
    If you installed and configured Ansible correctly, you will get output similar to this:

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    # Output
    server1 | SUCCESS => {
        "changed": false, 
        "ping": "pong"
    }
    server2 | SUCCESS => {
        "changed": false, 
        "ping": "pong"
    }
    server3 | SUCCESS => {
        "changed": false, 
        "ping": "pong"
    }

Once you get a pong reply back from a host, it means you’re ready to run Ansible commands and playbooks on that server.

Note: If you are unable to get a successful response back from your servers, check our Ansible Cheat Sheet Guide for more information on how to run Ansible commands with custom connection options.


Ansible Playbook

This Ansible playbook provides an alternative to manually running through the procedure outlined in our guide on How To Install and Use Docker on Ubuntu 18.04.

Running this playbook will perform the following actions on your Ansible hosts:

  • Install aptitude, which is preferred by Ansible as an alternative to the apt package manager.
  • Install the required system packages.
  • Install the Docker GPG APT key.
  • Add the official Docker repository to the apt sources.
  • Install Docker.
  • Install the Python Docker module via pip.
  • Pull the default image specified by default_container_image from Docker Hub.
  • Create the number of containers defined by create_containers field, each using the image defined by default_container_image, and execute the command defined in default_container_command in each new container.

Once the playbook has finished running, you will have a number of containers created based on the options you defined within your configuration variables.


Playbook Guide

To get started, we’ll download the contents of the playbook to your Ansible Control Node. For your convenience, the contents of the playbook are also included in the next section of this guide.

Use curl to download this playbook from the command line:

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curl -L https://raw.githubusercontent.com/do-community/ansible-playbooks \
/master/docker/ubuntu1804.yml -o docker_ubuntu.yml

This will download the contents of the playbook to a file named docker_ubuntu.yml in your current working directory. You can examine the contents of the playbook by opening the file with your command-line editor of choice:

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vim docker_ubuntu.yml

Once you’ve opened the playbook file, you should notice a section named vars with variables that require your attention:

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# docker_ubuntu.yml
. . .
vars:
  create_containers: 4
  default_container_name: docker
  default_container_image: ubuntu
  default_container_command: sleep 1d
. . .

Here’s what these variables mean:

  • create_containers: The number of containers to create.
  • default_container_name: Default container name.
  • default_container_image: Default Docker image to be used when creating containers.
  • default_container_command: Default command to run on new containers.

Once you’re done updating the variables inside docker_ubuntu.yml, save and close the file. If you used vim, do so by pressing CTRL + X, Y, then ENTER.

You’re now ready to run this playbook on one or more servers. Most playbooks are configured to be executed on all servers from your inventory, by default. We can use the -l flag to make sure that only a subset of servers, or a single server, is affected by the playbook. To execute the playbook only on server1, you can use the following command:

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ansible-playbook docker_ubuntu.yml -l server1

You will get output similar to this:

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# Output
...
TASK [Add Docker GPG apt Key] ********************************************************************************************************************
changed: [server1]

TASK [Add Docker Repository] *********************************************************************************************************************
changed: [server1]

TASK [Update apt and install docker-ce] **********************************************************************************************************
changed: [server1]

TASK [Install Docker Module for Python] **********************************************************************************************************
changed: [server1]

TASK [Pull default Docker image] *****************************************************************************************************************
changed: [server1]

TASK [Create default containers] *****************************************************************************************************************
changed: [server1] => (item=1)
changed: [server1] => (item=2)
changed: [server1] => (item=3)
changed: [server1] => (item=4)

PLAY RECAP ***************************************************************************************************************************************
server1                  : ok=9    changed=8    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

Note: For more information on how to run Ansible playbooks, check our Ansible Cheat Sheet Guide.

When the playbook is finished running, log in via SSH to the server provisioned by Ansible and run docker ps -a to check if the containers were successfully created:

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sudo docker ps -a

Now the containers defined in the playbook were created successfully. Since this was the last task in the playbook, it also confirms that the playbook was fully executed on this server.


Playbook Contents

You can find the Docker playbook featured in this post in the ansible-playbooks repository within the DigitalOcean Community GitHub organization. To copy or download the script contents directly, click the Raw button towards the top of the script, or click here to view the raw contents directly.

The full contents are also included here for your convenience:

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# docker_ubuntu.yml

---
- hosts: all
  become: true
  vars:
    create_containers: 4
    default_container_name: docker
    default_container_image: ubuntu
    default_container_command: sleep 1d

  tasks:
    - name: Install aptitude using apt
      apt: name=aptitude state=latest update_cache=yes force_apt_get=yes

    - name: Install required system packages
      apt: name={{ item }} state=latest update_cache=yes
      loop: [ 'apt-transport-https', 'ca-certificates', 'curl', 'software-properties-common', 'python3-pip', 'virtualenv', 'python3-setuptools']

    - name: Add Docker GPG apt Key
      apt_key:
        url: https://download.docker.com/linux/ubuntu/gpg
        state: present

    - name: Add Docker Repository
      apt_repository:
        repo: deb https://download.docker.com/linux/ubuntu bionic stable
        state: present

    - name: Update apt and install docker-ce
      apt: update_cache=yes name=docker-ce state=latest

    - name: Install Docker Module for Python
      pip:
        name: docker

    # Pull image specified by variable default_image from the Docker Hub
    - name: Pull default Docker image
      docker_image:
        name: "{{ default_container_image }}"
        source: pull

    # Creates the number of containers defined by the variable create_containers, using default values
    - name: Create default containers
      docker_container:
        name: "{{ default_container_name }}{{ item }}"
        image: "{{ default_container_image }}"
        command: "{{ default_container_command }}"
        state: present
      with_sequence: count={{ create_containers }}

Feel free to modify this playbook to best suit your individual needs within your own workflow. For example, you could use the docker_image module to push images to Docker Hub or the docker_container module to set up container networks.


Conclusion

Automating your infrastructure setup can not only save you time, but it also helps to ensure that your servers will follow a standard configuration that can be customized to your needs. With the distributed nature of modern applications and the need for consistency between different staging environments, automation like this has become a central component in many teams’ development processes.

In this post, we demonstrated how to use Ansible to automate the process of installing and setting up Docker on a remote server. Because each individual typically has different needs when working with containers, we encourage you to check out the official Ansible documentation for more information and use cases of the docker_container Ansible module.