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Docker_Tips.md

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Docker Tips/Shortcuts

Tips for using Docker container/virtualization platform.

Docker Terminology

  • Dockerfile: A specification (plan) for building a Docker image.
  • Image: A template for Docker containers that has a specific purpose. Basically, the image provides the custom file system structure required for the application.
  • Container: An instance (either running or finished) of an image for running process/application. Containers are isolated from other processes on the host machine using Linux kernel namespaces and cgroups, which have been part of Linux for a long time.

Common Commands

Command Action
docker run -it ubuntu bash Run (start) Docker image named ubuntu, downloading it, if necessary, and execute bash application in container in interactive (-it) mode.
docker ps -a List all (-a) of the containers, running or not.
docker start --attach container_name Launch existing ("reuse") container with name container_name and show output (--attach).
docker stop container_name Stop running container named container_name.
docker rm -f container_name Remove/delete container named container_name and force (-f) delete if container is still running.
docker image ls List the Docker images downloaded to the system.

Basic Docker Examples

Publish local directory with Docker Nginx image

In this example, our HTML, CSS, etc. files are in the /var/local/html directory.

docker run -v /var/local/html:/usr/share/nginx/html:ro -p 8080:80 -d nginx

Here's what the various parts of the command mean:

  • -v /var/local/html:/usr/share/nginx/html:ro: Maps the local /var/local/html directory with our web page resources to /usr/share/nginx/html in the container. Specifying ro tells Dockers to mount it in read-only mode, meaning that the container can't/won't make any changes.
  • -p 8080:80: Maps network service port 80 in the container to port 8080 on the host system (the system running the Docker instance). This means that you would access the web site at port 8080 from the host (e.g., http://127.0.0.1:8080/).
  • -d: Detaches the container from the command line session. In other words, the container continues running in the background.
  • nginx: The name of the Docker image to use for the container.

Reference1

Build a containerized Node.JS/Express.JS application with PostgreSQL using Docker Compose

Reference GitHub Repository

Install Docker on Ubuntu from Official Repository

Remove Any Version of Docker Installed from Ubuntu Repositories

sudo apt-get purge -y docker-engine docker docker.io containerd runc
sudo apt-get autoremove -y --purge docker-engine docker docker.io containerd runc

Install Prerequisite Packages for HTTPS Support

sudo apt-get install -y apt-transport-https ca-certificates curl software-properties-common gnupg lsb-release

Add GPG Key for Official Docker Repository

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

Add Official Docker Repository to APT Sources

sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
sudo apt-get update

Check to Ensure Use of Docker CE (Community Edition) Repository

sudo apt-cache policy docker-ce

You should see output similar to the following. The most important aspect is that it references the https://download.docker.com/ repository.

docker-ce:
  Installed: (none)
  Candidate: 5:20.10.6~3-0~ubuntu-focal
  Version table:
 *** 5:20.10.6~3-0~ubuntu-focal 500
        500 https://download.docker.com/linux/ubuntu focal/stable amd64 Packages

Install Docker from Repository

sudo apt-get install -y docker-ce

Ensure that Docker Service Started Successfully

sudo systemctl status docker

You should see output similar to the following. The most important aspect is that it shows that the service is active (running).

● docker.service - Docker Application Container Engine
     Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
     Active: active (running) since Thu 2021-05-06 14:21:00 CDT; 12s ago
TriggeredBy: ● docker.socket
       Docs: https://docs.docker.com
   Main PID: 746864 (dockerd)
      Tasks: 11
     Memory: 68.2M
     CGroup: /system.slice/docker.service
             └─746864 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

Add Your User Account to docker Group to Run Docker Without Entering Password

sudo usermod -aG docker ${USER}

You will have to logout (not just close your shell/terminal window) to get permissions for the docker group. Of course, you can proceed without these permissions, but you'll need to enter your account password whenever you rung the docker (or related) command.

As an alternative, you can open a sub-shell with the new docker group member with this command:

exec su -l ${USER}

After logging in, run id -nG to confirm that you are a member of the docker group.

Verify Docker Installation

docker run hello-world

You should see Docker pull down (or perhaps update, if you had Docker previously installed) the "Hello, World" Docker image and launch it. You'll see some output including the message Hello from Docker!, which confirms successfully installation and configuration.

Reference1
Reference2

Install Docker Compose Utility

The Docker Compose tool allows you to build Docker applications made up of multiple containers and services from a single YAML configuration file, docker-compose.yml. Many packaged applications that use Docker require/expect Docker Compose to be installed. To install it, run:

sudo curl -L "https://github.com/docker/compose/releases/download/1.29.1/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose
sudo chmod +x /usr/local/bin/docker-compose

Reference

Completely Uninstall and Remove Docker from Ubuntu

NOTE: This will delete all Docker images, containers, volumes, and user-created configurations on your system.

Determine which Docker-related packages are installed

dpkg -l | grep -i docker

Stop the Docker service

sudo systemctl stop docker

Uninstall all of the Docker-related application packages

sudo apt-get purge -y docker-engine docker docker.io docker-ce docker-ce-cli
sudo apt-get autoremove -y --purge docker-engine docker docker.io docker-ce

Delete the Docker Compose and Docker Machine application files

sudo rm -rf /usr/local/bin/docker-machine /usr/local/bin/docker-machine /etc/bash_completion.d/docker-machine*

Delete the images, containers, and volumes

sudo rm -rf /var/lib/docker /etc/docker
sudo rm /etc/apparmor.d/docker
sudo groupdel docker
sudo rm -rf /var/run/docker.sock

Reference

Run Docker on Windows 10 without Docker Desktop

Docker changed their licensing model recently and many developers must now use the new subscription-based model to use Docker Desktop tool. However, frequently, developers only use the command-line tools in their day-to-day work and so the Docker Desktop tool is overkill for their needs anyway.

This article explains how to run Docker on Windows in a very simple command-line-only configuration. And it works on even relatively old Windows 10 systems, including those with Windows Subsystem for Linux (WSL) 1. Essentially, we will be running the Docker daemon (or "service", if you prefer) in a Virtualbox or Hyper-V virtual machine (VM) and accessing it from our Windows 10 host machine in WSL or PowerShell (or Windows Command Prompt).

What You Need

To use this configuration, we will use the following environment.

  • Windows 10
  • WSL 1 or WSL 2 with Ubuntu 20.04
  • Virtualbox 6.2 with Ubuntu 20.04 guest or Hyper-V with Ubuntu 20.04 guest As noted, we can use either Virtualbox or Hyper-V for the virtualization platform. This allows Windows 10 Home users to use this process, even though they do not Hyper-V support on their platform.

Install Ubuntu 20.04 in WSL

Install Ubuntu 20.04 (or 18.04) in WSL according to the standard installation process. Here is a brief outline of the process.

  1. To install WSL, open PowerShell (or Windows Command Prompt) and run
wsl.exe --install
  1. By default, the WSL installation will install Ubuntu. You can also check for other available distributions and versions:
wsl.exe --list --online
  1. Then, you can install one of the available distributions from this list:
wsl.exe --install -d <distroname>

where <distroname> is the name from the earlier list, such as ubuntu2004.

Install Virtualbox or Hyper-V Virtualization Platform

As explained earlier, you can use either Virtualbox or Hyper-V virtualization platform, depending on your preference and what is supported in your environment. Simply follow the standard installation process for the selected tool. (Note that you cannot use both Virtualbox and Hyper-V simultaneously due to the Hyper-V architecture.)

Install Ubuntu Linux Guest in Virtualbox or Hyper-V

After installing Virtualbox or Hyper-V, you will need to install Ubuntu (or other Debian-based) Linux as a guest operating system (OS) on the virtualization platform. You can install a standard GUI version or a very minimal command-line only version. This guest OS will only run Docker daemon (or "service") process, so the OS GUI is entirely optional.

Follow the standard installation process for either Virtualbox or Hyper-V for installing guest OSes. Make sure to allocate at least 2GB of RAM to the guest.

Install Docker Daemon on Ubuntu Linux Guest in Virtualbox or Hyper-V

Once you've successfully installed Ubuntu as a guest OS in Virtualbox or Hyper-V, in that Ubuntu instance (and not the WSL instance yet!), install the Docker daemon application. Again, we will be running the Docker daemon in the guest virtual machine (VM) and accessing it from our Windows 10 host machine.

Update the Ubuntu packages.

sudo apt update
sudo apt upgrade -yy

Remove any existing Docker installation from standard Ubuntu repositories. (If you just installed Ubuntu guest OS, it's unlikely that they are installed, but it doesn't hurt to check.)

sudo apt remove docker docker-engine docker.io containerd runc -y

Configure the official Docker repository and install Docker from it.

source /etc/os-release
curl -fsSL https://download.docker.com/linux/${ID}/gpg | sudo apt-key add -
echo "deb [arch=amd64] https://download.docker.com/linux/${ID} ${VERSION_CODENAME} stable" | sudo tee /etc/apt/sources.list.d/docker.list
sudo apt update
sudo apt install docker-ce docker-ce-cli containerd.io

The installation process creates a docker group in Linux. We need to add our user to that group to allow us to run Docker commands without using sudo.

sudo usermod -a -G docker ${USER}

You must close the terminal window and open a new one (or log out and log back in, if you are using a console/command-prompt only VM) to get a session in which your user belongs to the docker group. To confirm, run the groups command and ensure that docker is included in the list (it will probably be the last one).

To verify that everything is working properly, while still in our Linux guest VM, run docker info. You should see some output divided up into Client and Server sections. See the docker info command documentation for details and examples.

Configure Docker Daemon for External Access on Ubuntu Linux Guest in Virtualbox or Hyper-V

Now that the Docker daemon is installed and working, we need to make it accessible outside of the Virtualbox or Hyper-V guest OS. For our case, to simplify things, we will configure it without encryption. Obviously, this involves some risk, but presumably, we will only be accessing from within the same machine. You can learn more about this in the Docker security documentation.

Create a systemd service directory for our configuration and create the daemon (service) configuration file.

sudo mkdir -p /etc/systemd/system/docker.service.d
sudo nano /etc/systemd/system/docker.service.d/options.conf

In options.conf add the following lines and save the file. Note that there indeed two lines starting with ExecStart=.

[Service]
ExecStart=
ExecStart=/usr/bin/dockerd -H unix:// -H tcp://0.0.0.0:2375

Refresh the systemd configuration and restart Docker.

sudo systemctl daemon-reload
sudo systemctl restart docker

Presumably, you won't receive any errors on restart. In any case, you can check that the Docker daemon restarted (is running) by running sudo systemctl status docker, if you like.

Basically, this configuration allows local connections from within the Virtualbox or Hyper-V guest OS VM via -H unix:// and from any external client over TCP on port 2375 via -H tcp://0.0.0.0:2375.

Determine the IP Address of Ubuntu Linux Guest in Virtualbox or Hyper-V

The final step involving the Ubuntu Linux guest OS in Virtualbox or Hyper-V is to determine its IPv4 address. We need this IP address to use on the host (WSL or PowerShell) to connect to the Docker daemon remotely.

References

Use Docker for Windows in WSL1
How to run docker on Windows without Docker Desktop
Setting Up Docker for Windows and WSL to Work Flawlessly
Docker Tip #73: Connecting to a Remote Docker Daemon