How to Use Ansible to Install and Set Up Docker on Ubuntu 18.04

In this guide, you'll learn how to use Ansible to automate the process of installing and setting up Docker on a remote server.

Introduction

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 guide explains how to use Ansible to automate the steps contained in our guide on How To Install and Use Docker on Ubuntu 18.04. 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.

Pre-Flight 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.
• 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.

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:

ansible -m ping all

This command will use Ansible's built-in [ping](https://docs.ansible.com/ansible/latest/modules/ping_module.html) 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:

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.

What Does this Playbook Do?

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:

1. Install aptitude, which is preferred by Ansible as an alternative to the apt package manager.
2. Install the required system packages.
3. Install the Docker GPG APT key.
4. Add the official Docker repository to the apt sources.
5. Install Docker.
6. Install the Python Docker module via pip.
7. Pull the default image specified by default_container_image from Docker Hub.
8. 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.

How to Use this Playbook

To get started, we'll download the contents of the playbook to your Ansible Control Node.

Use curl to download this playbook from the command line:

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:

nano docker_ubuntu.yml

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

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 nano, 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:

ansible-playbook docker_ubuntu.yml -l server1

You will get output similar to this:

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   

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:

sudo docker ps -a

You should see output similar to this:

CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
a3fe9bfb89cf        ubuntu              "sleep 1d"          5 minutes ago       Created                                 docker4
8799c16cde1e        ubuntu              "sleep 1d"          5 minutes ago       Created                                 docker3
ad0c2123b183        ubuntu              "sleep 1d"          5 minutes ago       Created                                 docker2
b9350916ffd8        ubuntu              "sleep 1d"          5 minutes ago       Created                                 docker1

This means 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.

The Playbook Contents

You can find the Docker playbook featured in this tutorial in the ansible-playbooks repository 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:

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](https://morioh.com/p/4e215b4c64de) module to push images to Docker Hub or the [docker_container](https://morioh.com/p/c310f568c20d) 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 guide, 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.

This entry-level guide will tell you why and how to Dockerize your WordPress projects.

This entry-level guide will tell you why and how to Dockerize your WordPress projects.

In this article, you'll install and use Docker on Ubuntu 18.04. You'll install Docker itself, work with containers and images, and push an image to a Docker Repository.

In this article, you'll install and use Docker on Ubuntu 18.04. You'll install Docker itself, work with containers and images, and push an image to a Docker Repository.

Introduction

Docker is an application that simplifies the process of managing application processes in containers. Containers let you run your applications in resource-isolated processes. They're similar to virtual machines, but containers are more portable, more resource-friendly, and more dependent on the host operating system.

Prerequisites

To follow this tutorial, you will need the following:

• One Ubuntu 18.04 server
• An account on Docker Hub if you wish to create your own images and push them to Docker Hub, as shown in Steps 7 and 8.

Step 1 — Installing Docker

The Docker installation package available in the official Ubuntu repository may not be the latest version. To ensure we get the latest version, we'll install Docker from the official Docker repository. To do that, we'll add a new package source, add the GPG key from Docker to ensure the downloads are valid, and then install the package.

First, update your existing list of packages:

sudo apt update

Next, install a few prerequisite packages which let apt use packages over HTTPS:

sudo apt install apt-transport-https ca-certificates curl software-properties-common

Then add the GPG key for the official Docker repository to your system:

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -

Add the Docker repository to APT sources:

sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu bionic stable"

Next, update the package database with the Docker packages from the newly added repo:

sudo apt update

Make sure you are about to install from the Docker repo instead of the default Ubuntu repo:

apt-cache policy docker-ce

You'll see output like this, although the version number for Docker may be different:

Output of apt-cache policy docker-ce

docker-ce:
  Installed: (none)
  Candidate: 18.03.1~ce~3-0~ubuntu
  Version table:
     18.03.1~ce~3-0~ubuntu 500
        500 https://download.docker.com/linux/ubuntu bionic/stable amd64 Packages

Notice that docker-ce is not installed, but the candidate for installation is from the Docker repository for Ubuntu 18.04 (bionic).

Finally, install Docker:

sudo apt install docker-ce

Docker should now be installed, the daemon started, and the process enabled to start on boot. Check that it's running:

sudo systemctl status docker

The output should be similar to the following, showing that the service is active and running:

Output
● docker.service - Docker Application Container Engine
   Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
   Active: active (running) since Thu 2018-07-05 15:08:39 UTC; 2min 55s ago
     Docs: https://docs.docker.com
 Main PID: 10096 (dockerd)
    Tasks: 16
   CGroup: /system.slice/docker.service
           ├─10096 /usr/bin/dockerd -H fd://
           └─10113 docker-containerd --config /var/run/docker/containerd/containerd.toml

Installing Docker now gives you not just the Docker service (daemon) but also the docker command line utility, or the Docker client. We'll explore how to use the docker command later in this tutorial.

Step 2 — Executing the Docker Command Without Sudo (Optional)

By default, the docker command can only be run the root user or by a user in the docker group, which is automatically created during Docker's installation process. 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 this:

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

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

sudo usermod -aG docker ${USER}

To apply the new group membership, log out of the server and back in, or type the following:

su - ${USER}

You will be prompted to enter your user's password to continue.

Confirm that your user is now added to the docker group by typing:

id -nG

Output
sammy sudo docker

If you need to add a user to the docker group that you're not logged in as, declare that username explicitly using:

sudo usermod -aG docker username

The rest of this article assumes you are running the docker command as a user in the docker group. If you choose not to, please prepend the commands with sudo.

Let's explore the docker command next.

Step 3 — Using the Docker Command

Using docker consists of passing it a chain of options and commands followed by arguments. The syntax takes this form:

docker [option] [command] [arguments]

To view all available subcommands, type:

docker

As of Docker 18, the complete list of available subcommands includes:

Output

  attach      Attach local standard input, output, and error streams to a running container
  build       Build an image from a Dockerfile
  commit      Create a new image from a container's changes
  cp          Copy files/folders between a container and the local filesystem
  create      Create a new container
  diff        Inspect changes to files or directories on a container's filesystem
  events      Get real time events from the server
  exec        Run a command in a running container
  export      Export a container's filesystem as a tar archive
  history     Show the history of an image
  images      List images
  import      Import the contents from a tarball to create a filesystem image
  info        Display system-wide information
  inspect     Return low-level information on Docker objects
  kill        Kill one or more running containers
  load        Load an image from a tar archive or STDIN
  login       Log in to a Docker registry
  logout      Log out from a Docker registry
  logs        Fetch the logs of a container
  pause       Pause all processes within one or more containers
  port        List port mappings or a specific mapping for the container
  ps          List containers
  pull        Pull an image or a repository from a registry
  push        Push an image or a repository to a registry
  rename      Rename a container
  restart     Restart one or more containers
  rm          Remove one or more containers
  rmi         Remove one or more images
  run         Run a command in a new container
  save        Save one or more images to a tar archive (streamed to STDOUT by default)
  search      Search the Docker Hub for images
  start       Start one or more stopped containers
  stats       Display a live stream of container(s) resource usage statistics
  stop        Stop one or more running containers
  tag         Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE
  top         Display the running processes of a container
  unpause     Unpause all processes within one or more containers
  update      Update configuration of one or more containers
  version     Show the Docker version information
  wait        Block until one or more containers stop, then print their exit codes

To view the options available to a specific command, type:

docker docker-subcommand --help

To view system-wide information about Docker, use:

docker info

Let's explore some of these commands. We'll start by working with images.

Step 4 — Working with Docker Images

Docker containers are built from Docker images. By default, Docker pulls these images from Docker Hub, a Docker registry managed by Docker, the company behind the Docker project. Anyone can host their Docker images on Docker Hub, so most applications and Linux distributions you'll need will have images hosted there.

To check whether you can access and download images from Docker Hub, type:

docker run hello-world

The output will indicate that Docker in working correctly:

Output
Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
9bb5a5d4561a: Pull complete
Digest: sha256:3e1764d0f546ceac4565547df2ac4907fe46f007ea229fd7ef2718514bcec35d
Status: Downloaded newer image for hello-world:latest

Hello from Docker!
This message shows that your installation appears to be working correctly.
...

Docker was initially unable to find the hello-world image locally, so it downloaded the image from Docker Hub, which is the default repository. Once the image downloaded, Docker created a container from the image and the application within the container executed, displaying the message.

You can search for images available on Docker Hub by using the docker command with the search subcommand. For example, to search for the Ubuntu image, type:

docker search ubuntu

The script will crawl Docker Hub and return a listing of all images whose name match the search string. In this case, the output will be similar to this:

Output
NAME                                                      DESCRIPTION                                     STARS               OFFICIAL            AUTOMATED
ubuntu                                                    Ubuntu is a Debian-based Linux operating sys…   7917                [OK]
dorowu/ubuntu-desktop-lxde-vnc                            Ubuntu with openssh-server and NoVNC            193                                     [OK]
rastasheep/ubuntu-sshd                                    Dockerized SSH service, built on top of offi…   156                                     [OK]
ansible/ubuntu14.04-ansible                               Ubuntu 14.04 LTS with ansible                   93                                      [OK]
ubuntu-upstart                                            Upstart is an event-based replacement for th…   87                  [OK]
neurodebian                                               NeuroDebian provides neuroscience research s…   50                  [OK]
ubuntu-debootstrap                                        debootstrap --variant=minbase --components=m…   38                  [OK]
1and1internet/ubuntu-16-nginx-php-phpmyadmin-mysql-5      ubuntu-16-nginx-php-phpmyadmin-mysql-5          36                                      [OK]
nuagebec/ubuntu                                           Simple always updated Ubuntu docker images w…   23                                      [OK]
tutum/ubuntu                                              Simple Ubuntu docker images with SSH access     18
i386/ubuntu                                               Ubuntu is a Debian-based Linux operating sys…   13
ppc64le/ubuntu                                            Ubuntu is a Debian-based Linux operating sys…   12
1and1internet/ubuntu-16-apache-php-7.0                    ubuntu-16-apache-php-7.0                        10                                      [OK]
1and1internet/ubuntu-16-nginx-php-phpmyadmin-mariadb-10   ubuntu-16-nginx-php-phpmyadmin-mariadb-10       6                                       [OK]
eclipse/ubuntu_jdk8                                       Ubuntu, JDK8, Maven 3, git, curl, nmap, mc, …   6                                       [OK]
codenvy/ubuntu_jdk8                                       Ubuntu, JDK8, Maven 3, git, curl, nmap, mc, …   4                                       [OK]
darksheer/ubuntu                                          Base Ubuntu Image -- Updated hourly             4                                       [OK]
1and1internet/ubuntu-16-apache                            ubuntu-16-apache                                3                                       [OK]
1and1internet/ubuntu-16-nginx-php-5.6-wordpress-4         ubuntu-16-nginx-php-5.6-wordpress-4             3                                       [OK]
1and1internet/ubuntu-16-sshd                              ubuntu-16-sshd                                  1                                       [OK]
pivotaldata/ubuntu                                        A quick freshening-up of the base Ubuntu doc…   1
1and1internet/ubuntu-16-healthcheck                       ubuntu-16-healthcheck                           0                                       [OK]
pivotaldata/ubuntu-gpdb-dev                               Ubuntu images for GPDB development              0
smartentry/ubuntu                                         ubuntu with smartentry                          0                                       [OK]
ossobv/ubuntu
...

In the OFFICIAL column, OK indicates an image built and supported by the company behind the project. Once you've identified the image that you would like to use, you can download it to your computer using the pull subcommand.

Execute the following command to download the official ubuntu image to your computer:

docker pull ubuntu

You'll see the following output:

Output
Using default tag: latest
latest: Pulling from library/ubuntu
6b98dfc16071: Pull complete
4001a1209541: Pull complete
6319fc68c576: Pull complete
b24603670dc3: Pull complete
97f170c87c6f: Pull complete
Digest: sha256:5f4bdc3467537cbbe563e80db2c3ec95d548a9145d64453b06939c4592d67b6d
Status: Downloaded newer image for ubuntu:latest

After an image has been downloaded, you can then run a container using the downloaded image with the run subcommand. As you saw with the hello-world example, if an image has not been downloaded when docker is executed with the run subcommand, the Docker client will first download the image, then run a container using it.

To see the images that have been downloaded to your computer, type:

docker images

The output should look similar to the following:

Output
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
ubuntu              latest              113a43faa138        4 weeks ago         81.2MB
hello-world         latest              e38bc07ac18e        2 months ago        1.85kB

As you'll see later in this tutorial, images that you use to run containers can be modified and used to generate new images, which may then be uploaded (pushed is the technical term) to Docker Hub or other Docker registries.

Let's look at how to run containers in more detail.

Step 5 — Running a Docker Container

The hello-world container you ran in the previous step is an example of a container that runs and exits after emitting a test message. Containers can be much more useful than that, and they can be interactive. After all, they are similar to virtual machines, only more resource-friendly.

As an example, let's run a container using the latest image of Ubuntu. The combination of the -i and -t switches gives you interactive shell access into the container:

docker run -it ubuntu

Your command prompt should change to reflect the fact that you're now working inside the container and should take this form:

Output
[email protected]:/#

Note the container id in the command prompt. In this example, it is d9b100f2f636. You'll need that container ID later to identify the container when you want to remove it.

Now you can run any command inside the container. For example, let's update the package database inside the container. You don't need to prefix any command with sudo, because you're operating inside the container as the root user:

apt update

Then install any application in it. Let's install Node.js:

apt install nodejs

This installs Node.js in the container from the official Ubuntu repository. When the installation finishes, verify that Node.js is installed:

node -v

You'll see the version number displayed in your terminal:

Output
v8.10.0

Any changes you make inside the container only apply to that container.

To exit the container, type exit at the prompt.

Let's look at managing the containers on our system next.

Step 6 — Managing Docker Containers

After using Docker for a while, you'll have many active (running) and inactive containers on your computer. To view the active ones, use:

docker ps

You will see output similar to the following:

Output
CONTAINER ID        IMAGE               COMMAND             CREATED             

In this tutorial, you started two containers; one from the hello-world image and another from the ubuntu image. Both containers are no longer running, but they still exist on your system.

To view all containers — active and inactive, run docker ps with the -a switch:

docker ps -a

You'll see output similar to this:

d9b100f2f636        ubuntu              "/bin/bash"         About an hour ago   Exited (0) 8 minutes ago                           sharp_volhard
01c950718166        hello-world         "/hello"            About an hour ago   Exited (0) About an hour ago                       festive_williams

To view the latest container you created, pass it the -l switch:

docker ps -l

    CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS                      PORTS               NAMES
    d9b100f2f636        ubuntu              "/bin/bash"         About an hour ago   Exited (0) 10 minutes ago                       sharp_volhard

To start a stopped container, use docker start, followed by the container ID or the container's name. Let's start the Ubuntu-based container with the ID of d9b100f2f636:

docker start d9b100f2f636

The container will start, and you can use docker ps to see its status:

CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
d9b100f2f636        ubuntu              "/bin/bash"         About an hour ago   Up 8 seconds                            sharp_volhard

To stop a running container, use docker stop, followed by the container ID or name. This time, we'll use the name that Docker assigned the container, which is sharp_volhard:

docker stop sharp_volhard

Once you've decided you no longer need a container anymore, remove it with the docker rm command, again using either the container ID or the name. Use the docker ps -a command to find the container ID or name for the container associated with the hello-world image and remove it.

docker rm festive_williams

You can start a new container and give it a name using the --name switch. You can also use the --rm switch to create a container that removes itself when it's stopped. See the docker run help command for more information on these options and others.

Containers can be turned into images which you can use to build new containers. Let's look at how that works.

Step 7 — Committing Changes in a Container to a Docker Image

When you start up a Docker image, you can create, modify, and delete files just like you can with a virtual machine. The changes that you make will only apply to that container. You can start and stop it, but once you destroy it with the docker rm command, the changes will be lost for good.

This section shows you how to save the state of a container as a new Docker image.

After installing Node.js inside the Ubuntu container, you now have a container running off an image, but the container is different from the image you used to create it. But you might want to reuse this Node.js container as the basis for new images later.

Then commit the changes to a new Docker image instance using the following command.

docker commit -m "What you did to the image" -a "Author Name" container_id repository/new_image_name

The -m switch is for the commit message that helps you and others know what changes you made, while -a is used to specify the author. The container_id is the one you noted earlier in the tutorial when you started the interactive Docker session. Unless you created additional repositories on Docker Hub, the repository is usually your Docker Hub username.

For example, for the user sammy, with the container ID of d9b100f2f636, the command would be:

docker commit -m "added Node.js" -a "sammy" d9b100f2f636 sammy/ubuntu-nodejs

When you commit an image, the new image is saved locally on your computer. Later in this tutorial, you'll learn how to push an image to a Docker registry like Docker Hub so others can access it.

Listing the Docker images again will show the new image, as well as the old one that it was derived from:

docker images

You'll see output like this:

Output
REPOSITORY               TAG                 IMAGE ID            CREATED             SIZE
sammy/ubuntu-nodejs   latest              7c1f35226ca6        7 seconds ago       179MB
ubuntu                   latest              113a43faa138        4 weeks ago         81.2MB
hello-world              latest              e38bc07ac18e        2 months ago        1.85kB

In this example, ubuntu-nodejs is the new image, which was derived from the existing ubuntu image from Docker Hub. The size difference reflects the changes that were made. And in this example, the change was that NodeJS was installed. So next time you need to run a container using Ubuntu with NodeJS pre-installed, you can just use the new image.

You can also build Images from a Dockerfile, which lets you automate the installation of software in a new image. However, that's outside the scope of this tutorial.

Now let's share the new image with others so they can create containers from it.

Step 8 — Pushing Docker Images to a Docker Repository

The next logical step after creating a new image from an existing image is to share it with a select few of your friends, the whole world on Docker Hub, or other Docker registry that you have access to. To push an image to Docker Hub or any other Docker registry, you must have an account there.

To push your image, first log into Docker Hub.

docker login -u docker-registry-username

You'll be prompted to authenticate using your Docker Hub password. If you specified the correct password, authentication should succeed.

Note: If your Docker registry username is different from the local username you used to create the image, you will have to tag your image with your registry username. For the example given in the last step, you would type:

docker tag sammy/ubuntu-nodejs docker-registry-username/ubuntu-nodejs

Then you may push your own image using:

docker push docker-registry-username/docker-image-name

To push the ubuntu-nodejs image to the sammy repository, the command would be:

docker push sammy/ubuntu-nodejs

The process may take some time to complete as it uploads the images, but when completed, the output will look like this:

Output
The push refers to a repository [docker.io/sammy/ubuntu-nodejs]
e3fbbfb44187: Pushed
5f70bf18a086: Pushed
a3b5c80a4eba: Pushed
7f18b442972b: Pushed
3ce512daaf78: Pushed
7aae4540b42d: Pushed
...

After pushing an image to a registry, it should be listed on your account's dashboard, like that show in the image below.

If a push attempt results in an error of this sort, then you likely did not log in:

Output
The push refers to a repository [docker.io/sammy/ubuntu-nodejs]
e3fbbfb44187: Preparing
5f70bf18a086: Preparing
a3b5c80a4eba: Preparing
7f18b442972b: Preparing
3ce512daaf78: Preparing
7aae4540b42d: Waiting
unauthorized: authentication required

Log in with docker login and repeat the push attempt. Then verify that it exists on your Docker Hub repository page.

You can now use docker pull sammy/ubuntu-nodejs to pull the image to a new machine and use it to run a new container.

Conclusion

In this tutorial you installed Docker, worked with images and containers, and pushed a modified image to Docker Hub.

Docker makes the process of deployment easier by containerizing your app ... done, we'll have a nice Ubuntu + nginx + uwsgi + Flask stack all working.

Docker makes the process of deployment easier by containerizing your app ... done, we'll have a nice Ubuntu + nginx + uwsgi + Flask stack all working.

Introduction

Docker is an open-source application that allows administrators to create, manage, deploy, and replicate applications using containers. Containers can be thought of as a package that houses dependencies that an application requires to run at an operating system level. This means that each application deployed using Docker lives in an environment of its own and its requirements are handled separately.

Flask is a web micro-framework that is built on Python. It is called a micro-framework because it does not require specific tools or plug-ins to run. The Flask framework is lightweight and flexible, yet highly structured, making it preferred over other frameworks.

Deploying a Flask application with Docker will allow you to replicate the application across different servers with minimal reconfiguration.

In this tutorial, you will create a Flask application and deploy it with Docker. This tutorial will also cover how to update an application after deployment.

Prerequisites

To follow this tutorial, you will need the following:

• A non-root user with sudo privileges configured by following the Initial Server Setup with Ubuntu 18.04 guide.
• One Ubuntu 18.04 server with Docker installed, set up by following this tutorial or with the DigitalOcean one-click Docker image.
• Nginx installed by following step one of the How To Install Nginx on Ubuntu 18.04 tutorial.

Step 1 — Setting Up the Flask Application

To get started, you will create a directory structure that will hold your Flask application. This tutorial will create a directory called TestApp in /var/www, but you can modify the command to name it whatever you'd like.

sudo mkdir /var/www/TestApp

Move in to the newly created TestApp directory:

cd /var/www/TestApp

Next, create the base folder structure for the Flask application:

sudo mkdir -p app/static app/templates 

The -p flag indicates that mkdir will create a directory and all parent directories that don't exist. In this case, mkdir will create the app parent directory in the process of making the static and templatesdirectories.

The app directory will contain all files related to the Flask application such as its views and blueprints. Views are the code you write to respond to requests to your application. Blueprints create application components and support common patterns within an application or across multiple applications.

The static directory is where assets such as images, CSS, and JavaScript files live. The templatesdirectory is where you will put the HTML templates for your project.

Now that the base folder structure is complete, create the files needed to run the Flask application. First, create an __init__.py file inside the app directory. This file tells the Python interpreter that the appdirectory is a package and should be treated as such.

Run the following command to create the file:

sudo nano app/__init__.py

Packages in Python allow you to group modules into logical namespaces or hierarchies. This approach enables the code to be broken down into individual and manageable blocks that perform specific functions.

Next, you will add code to the <strong>init</strong>.py that will create a Flask instance and import the logic from the views.py file, which you will create after saving this file. Add the following code to your new file:

/var/www/TestApp/__init__.py

from flask import Flask
app = Flask(__name__)
from app import views

Once you've added that code, save and close the file.

With the __init__.py file created, you're ready to create the views.py file in your app directory. This file will contain most of your application logic.

sudo nano app/views.py

Next, add the code to your views.py file. This code will return the hello world! string to users who visit your web page:

/var/www/TestApp/app/views.py

from app import app

@app.route('/')
def home():
   return "hello world!"

The @app.route line above the function is called a decorator. Decorators modify the function that follows it. In this case, the decorator tells Flask which URL will trigger the home() function. The hello world text returned by the home function will be displayed to the user on the browser.

With the views.py file in place, you're ready to create the uwsgi.ini file. This file will contain the uWSGIconfigurations for our application. uWSGI is a deployment option for Nginx that is both a protocol and an application server; the application server can serve uWSGI, FastCGI, and HTTP protocols.

To create this file, run the following command:

sudo nano uwsgi.ini

Next, add the following content to your file to configure the uWSGI server:

/var/www/TestApp/uwsgi.ini

[uwsgi]
module = main
callable = app
master = true

This code defines the module that the Flask application will be served from. In this case, this is the main.py file, referenced here as main. The callable option instructs uWSGI to use the app instance exported by the main application. The master option allows your application to keep running, so there is little downtime even when reloading the entire application.

Next, create the main.py file, which is the entry point to the application. The entry point instructs uWSGI on how to interact with the application.

sudo nano main.py

Next, copy and paste the following into the file. This imports the Flask instance named app from the application package that was previously created.

/var/www/TestApp/main.py

from app import app

Finally, create a requirements.txt file to specify the dependencies that the pip package manager will install to your Docker deployment:

sudo nano requirements.txt

Add the following line to add Flask as a dependency:

/var/www/TestApp/app/requirements.txt

Flask==1.0.2

This specifies the version of Flask to be installed. At the time of writing this tutorial, 1.0.2 is the latest Flask version. You can check for updates at the official website for Flask.

Save and close the file. You have successfully set up your Flask application and are ready to set up Docker.

Step 2 — Setting Up Docker

In this step you will create two files, Dockerfile and start.sh, to create your Docker deployment. The Dockerfile is a text document that contains the commands used to assemble the image. The start.shfile is a shell script that will build an image and create a container from the Dockerfile.

First, create the Dockerfile.

sudo nano Dockerfile

Next, add your desired configuration to the Dockerfile. These commands specify how the image will be built, and what extra requirements will be included.

/var/www/TestApp/Dockerfile

FROM tiangolo/uwsgi-nginx-flask:python3.6-alpine3.7
RUN apk --update add bash nano
ENV STATIC_URL /static
ENV STATIC_PATH /var/www/app/static
COPY ./requirements.txt /var/www/requirements.txt
RUN pip install -r /var/www/requirements.txt

In this example, the Docker image will be built off an existing image, tiangolo/uwsgi-nginx-flask, which you can find on DockerHub. This particular Docker image is a good choice over others because it supports a wide range of Python versions and OS images.

The first two lines specify the parent image that you'll use to run the application and install the bash command processor and the nano text editor. It also installs the git client for pulling and pushing to version control hosting services such as GitHub, GitLab, and Bitbucket. ENV STATIC_URL /static is an environment variable specific to this Docker image. It defines the static folder where all assets such as images, CSS files, and JavaScript files are served from.

The last two lines will copy the requirements.txt file into the container so that it can be executed, and then parses the requirements.txt file to install the specified dependencies.

Save and close the file after adding your configuration.

With your Dockerfile in place, you're almost ready to write your start.sh script that will build the Docker container. Before writing the start.sh script, first make sure that you have an open port to use in the configuration. To check if a port is free, run the following command:

sudo nc localhost 56733 < /dev/null; echo $?

If the output of the command above is 1, then the port is free and usable. Otherwise, you will need to select a different port to use in your start.sh configuration file.

Once you've found an open port to use, create the start.sh script:

sudo nano start.sh

The start.sh script is a shell script that will build an image from the Dockerfile and create a container from the resulting Docker image. Add your configuration to the new file:

/var/www/TestApp/start.sh

#!/bin/bash
app="docker.test"
docker build -t ${app} .
docker run -d -p 56733:80 \
  --name=${app} \
  -v $PWD:/app ${app}

The first line is called a shebang. It specifies that this is a bash file and will be executed as commands. The next line specifies the name you want to give the image and container and saves as a variable named app. The next line instructs Docker to build an image from your Dockerfile located in the current directory. This will create an image called docker.test in this example.

The last three lines create a new container named docker.test that is exposed at port 56733. Finally, it links the present directory to the /var/www directory of the container.

You use the -d flag to start a container in daemon mode, or as a background process. You include the -pflag to bind a port on the server to a particular port on the Docker container. In this case, you are binding port 56733 to port 80 on the Docker container. The -v flag specifies a Docker volume to mount on the container, and in this case, you are mounting the entire project directory to the /var/www folder on the Docker container.

Execute the start.sh script to create the Docker image and build a container from the resulting image:

sudo bash start.sh

Once the script finishes running, use the following command to list all running containers:

sudo docker ps

You will receive output that shows the containers:

Output
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                            NAMES
58b05508f4dd        docker.test         "/entrypoint.sh /sta…"   12 seconds ago      Up 3 seconds       443/tcp, 0.0.0.0:56733->80/tcp   docker.test

You will find that the docker.test container is running. Now that it is running, visit the IP address at the specified port in your browser: http://ip-address:56733

You'll see a page similar to the following:

In this step you have successfully deployed your Flask application on Docker. Next, you will use templates to display content to users.

Step 3 — Serving Template Files

Templates are files that display static and dynamic content to users who visit your application. In this step, you will create a HTML template to create a home page for the application.

Start by creating a home.html file in the app/templates directory:

sudo nano app/templates/home.html

Add the code for your template. This code will create an HTML5 page that contains a title and some text.

/var/www/TestApp/app/templates/home.html

<!doctype html>

<html lang="en-us">   
  <head>
    <meta charset="utf-8">
    <meta http-equiv="x-ua-compatible" content="ie=edge">
    <title>Welcome home</title>
  </head>

  <body>
    <h1>Home Page</h1>
    <p>This is the home page of our application.</p>
  </body> 
</html>

Save and close the file once you've added your template.

Next, modify the app/views.py file to serve the newly created file:

sudo nano app/views.py

First, add the following line at the beginning of your file to import the render_template method from Flask. This method parses an HTML file to render a web page to the user.

/var/www/TestApp/app/views.py

from flask import render_template
...

At the end of the file, you will also add a new route to render the template file. This code specifies that users are served the contents of the home.html file whenever they visit the /template route on your application.

/var/www/TestApp/app/views.py

...

@app.route('/template')
def template():
    return render_template('home.html')

The updated app/views.py file will look like this:

/var/www/TestApp/app/views.py

from flask import render_template
from app import app 

@app.route('/')
def home():
    return "Hello world!"

@app.route('/template')
def template():
    return render_template('home.html')

Save and close the file when done.

In order for these changes to take effect, you will need to stop and restart the Docker containers. Run the following command to rebuild the container:

sudo docker stop docker.test && sudo docker start docker.test

Visit your application at http://your-ip-address:56733/template to see the new template being served.

In this you've created a Docker template file to serve visitors on your application. In the next step you will see how the changes you make to your application can take effect without having to restart the Docker container.

Step 4 — Updating the Application

Sometimes you will need to make changes to the application, whether it is installing new requirements, updating the Docker container, or HTML and logic changes. In this section, you will configure touch-reload to make these changes without needing to restart the Docker container.

Python autoreloading watches the entire file system for changes and refreshes the application when it detects a change. Autoreloading is discouraged in production because it can become resource intensive very quickly. In this step, you will use touch-reload to watch for changes to a particular file and reload when the file is updated or replaced.

To implement this, start by opening your uwsgi.ini file:

sudo nano uwsgi.ini

Next, add the highlighted line to the end of the file:

/var/www/TestApp/uwsgi.ini

module = main
callable = app
master = true
touch-reload = /app/uwsgi.ini

This specifies a file that will be modified to trigger an entire application reload. Once you've made the changes, save and close the file.

To demonstrate this, make a small change to your application. Start by opening your app/views.py file:

sudo nano app/views.py

Replace the string returned by the home function:

/var/www/TestApp/app/views.py

from flask import render_template
from app import app

@app.route('/')
def home():
    return "<b>There has been a change</b>"

@app.route('/template')
def template():
    return render_template('home.html')

Save and close the file after you've made a change.

Next, if you open your application’s homepage at http://ip-address:56733, you will notice that the changes are not reflected. This is because the condition for reload is a change to the uwsgi.ini file. To reload the application, use touch to activate the condition:

sudo touch uwsgi.ini

Reload the application homepage in your browser again. You will find that the application has incorporated the changes:

n this step, you set up a touch-reload condition to update your application after making changes.

Conclusion

In this tutorial, you created and deployed a Flask application to a Docker container. You also configured touch-reload to refresh your application without needing to restart the container.

With your new application on Docker, you can now scale with ease. To learn more about using Docker, check out their official documentation.

Thank for reading !

Originally published on https://www.digitalocean.com