Docker_dev_tools

Reference: https://www.digitalocean.com/community/tutorials/how-to-install-and-use-docker-on-ubuntu-20-04

Introduction to Docker on Ubuntu 20.04

Docker simplifies managing application processes in containers, which are resource-isolated and more portable than virtual machines. This tutorial covers installing Docker Community Edition (CE) on Ubuntu 20.04, working with containers and images, and pushing an image to a Docker Repository.

Prerequisites

• Ubuntu 20.04 server with a sudo non-root user and a firewall
• Docker Hub account for creating and pushing images

Installation Steps

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:

Step-by-Step Docker Installation on Ubuntu 20.04

1. Update Package List

First, update your existing list of packages:

sudo apt update

2. Install Prerequisites

Install a few prerequisite packages which let apt use packages over HTTPS:

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

3. Add Docker’s GPG Key

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 -

4. Add Docker Repository

Add the Docker repository to APT sources:

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

This updates our package database with Docker packages from the newly added repo.

5. Verify Docker Repository

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

apt-cache policy docker-ce

Output Example:

docker-ce:
  Installed: (none)
  Candidate: 5:19.03.9~3-0~ubuntu-focal
  Version table:
     5:19.03.9~3-0~ubuntu-focal 500
        500 https://download.docker.com/linux/ubuntu focal/stable amd64 Packages

6. Install Docker

Finally, install Docker:

sudo apt install docker-ce

7. Check Docker Status

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

Output Example:

● docker.service - Docker Application Container Engine
     Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
     Active: active (running) since Tue 2020-05-19 17:00:41 UTC; 17s ago
TriggeredBy: ● docker.socket
       Docs: https://docs.docker.com
   Main PID: 24321 (dockerd)
      Tasks: 8
     Memory: 46.4M
     CGroup: /system.slice/docker.service
             └─24321 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

Step-by-Step: Executing Docker Command Without Sudo by using your current username (Optional)

1. Understanding Default Permissions

By default, the docker command can only be run by the root user or a user in the docker group. Attempting to run it otherwise results in: Output:

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

2. Add User to Docker Group

To avoid using sudo with docker, add your username to the docker group:

sudo usermod -aG docker ${USER}

3. Apply Group Membership

Log out and back in, or use:

su - ${USER}

Enter your user’s password to continue.

4. Verify Group Membership

Confirm your user is added to the docker group:

groups

Output:

sammy sudo docker

5. Add Another User (if needed)

To add a different user to the docker group:

sudo usermod -aG docker username

6. Run Docker Commands

Now, you can run Docker commands without sudo. If not, prepend commands with sudo.

Using Docker Commands

Docker commands follow this structure:

docker [option] [command] [arguments]

To see all subcommands, use:

docker

For help on a subcommand:

docker docker-subcommand --help

Working with Docker Images

Check Docker Hub access:

docker run hello-world

Search for images:

docker search ubuntu

Download an image:

docker pull ubuntu

List downloaded images:

docker images

Running a Docker Container

Run a container interactively:

docker run -it ubuntu # ???
docker exec -it container_name bash # go inside the container
exit # Exit the container

Managing Docker Containers

docker ps # List active containers
docker ps -a # List all containers
docker start container_id # Start a stopped container
docker stop container_id # Stop a running container
docker rm container_id # Remove a container

Committing Changes to a Docker Image

Save container state to a new image:

docker commit -m "message" -a "author" container_id repository/new_image_name

Pushing Docker Images to a Repository

Login to Docker Hub:

docker login -u docker-registry-username

Tag the image if necessary:

docker tag local-image:tagname new-repo:tagname

Push the image:

docker push docker-registry-username/image-name

Conclusion

You have now installed Docker, worked with images and containers, and pushed an image to Docker Hub. For more details and advanced tutorials, visit DigitalOcean's community tutorials.

For the complete tutorial, refer to the original guide.