Master Docker: From Basics to Advanced Container Management

0 Quick Start

Docker began as an internal hobby project at dotCloud.

Docker is written in Go.

The goal is a lightweight OS‑level virtualization solution.

It builds on Linux containers (LXC) and related technologies.

Containers start in seconds, far faster than traditional VMs.

Docker achieves high resource utilization; thousands of containers can run on a single host.

The following images compare Docker with traditional virtualization, showing that containers virtualize at the OS layer while VMs virtualize at the hardware layer.

1 Installation

The official website provides installation guides for Mac, Linux, and Windows; follow the official documentation.

Kitematic is a graphical tool (Visual Docker Container Management on Mac & Windows) that helps users explore Docker.

Daemon

When running the Docker daemon you can change the binding interface with the -H flag, e.g.: sudo /usr/bin/docker -d -H tcp://0.0.0.0:2375 To avoid typing the long command each time, set the environment variable:

export DOCKER_HOST="tcp://0.0.0.0:2375"

Graphical User Interface

Common web management interfaces include:

Shipyard

Portainer

2 Basic Concepts

Image

A read‑only template used to create Docker containers.

Based on a Union file system with layered structure.

Can be created, updated, or downloaded from others; it is the "source code" of a container.

Container

A running instance created from an image, with a writable top layer.

Can be started, stopped, or deleted; each container is isolated for security.

Essentially a lightweight Linux environment (including root privileges, process, user, and network spaces) plus the application.

Registry

A centralized place to store image files, public or private.

The largest public registry is Docker Hub.

Chinese public registries include Docker Pool.

After creating an image, use docker push to upload it; others can docker pull it.

The registry concept is similar to Git hosting services.

Docker uses a client/server architecture; the client sends requests to the Docker daemon.

3 Common Commands

Check Docker status: sudo docker info List running containers: docker ps (add -a to show all, -l for the latest).

A Simple Example

Run a basic container to print a message:

docker run ubuntu:14.04 /bin/echo 'Hello wdx!'

Start an interactive bash session: docker run -t -i ubuntu:14.04 /bin/bash The -t flag allocates a pseudo‑TTY; -i keeps STDIN open.

4 Container Overview

A container runs one or a group of applications with its own runtime environment, unlike a full VM that simulates an entire OS.

Containers can be created from an image or restarted from a stopped state; they are lightweight enough that users often delete and recreate them.

5 Running Containers

When creating a container with docker run, Docker performs:

Check for the image locally; pull from a public registry if missing.

Create and start a container from the image.

Mount a writable layer on top of the read‑only image.

Bridge a virtual network interface from the host to the container.

Assign an IP address from the host's address pool.

Execute the user‑specified application.

Terminate the container when the process exits.

Restart a stopped container with docker start.

6 Images

Pull an image from a registry: sudo docker pull ubuntu:12.04 Or from a custom registry: sudo docker pull dl.dockerpool.com:5000/ubuntu:12.04 List local images with docker images.

7 Running Images

Search Docker Hub for the whalesay image and run it:

docker run docker/whalesay cowsay boo

The command cowsay runs inside the container with argument boo.

8 Building Images

Create a Dockerfile in a new directory:

mkdir wdxtub; cd wdxtub

gedit Dockerfile

Add FROM docker/whalesay:latest as the base image.

Add commands, e.g., RUN apt-get -y update && apt-get install -y fortunes.

Specify the default command with CMD /usr/games/fortune -a | cowsay.

Build the image: sudo docker build -t wdx-whale . Verify with docker images.

9 Managing Images

Save an image to a tar file: docker save -o wdx-local-whale.tar wdxtub/wdx-whale Load it back with: docker load --input wdx-local-whale.tar Delete an image after removing dependent containers:

sudo docker rmi $(docker images -q -f "dangling=true")

10 Container Startup

Run a container in the background with -d:

docker run -d ubuntu:14.04 /bin/sh -c "while true; do echo hello world; sleep 1; done"

View its output with docker logs <containerid>.

11 Stop and Restart

Stop a container: docker stop <containerid> Restart a container:

docker restart <containerid>

12 Import/Export and Delete

Export a container to a tar archive: docker export <containerid> Import a tar archive as an image: cat ubuntu.tar | sudo docker import - test/ubuntu:v1.0 Delete a stopped container with docker rm; add -f to force removal of a running container.

13 Repository

A repository stores images; a registry is the server that hosts one or more repositories. For example, in dl.dockerpool.com/ubuntu, dl.dockerpool.com is the registry and ubuntu is the repository.