Master Docker: From Basics to Building Your Own Container Images

Why Docker?

Docker, released in 2013, has become a pivotal technology for simplifying software deployment by packaging applications with their dependencies into portable containers.

1. The environment‑configuration problem

Developers often struggle with differing OS settings, libraries, and environment variables across machines, leading to the classic "It works on my machine" issue. Recreating the exact environment on a new host can be time‑consuming and error‑prone.

2. Virtual machines

Virtual machines (VMs) run a full guest OS inside a host OS, providing isolation but at the cost of high resource consumption, redundant setup steps, and slow startup.

Heavy memory and disk usage

Extra steps such as user login

Long boot times

3. Linux containers

Linux Containers (LXC) solve many VM drawbacks by isolating processes at the kernel level rather than emulating an entire OS. Containers start quickly, use fewer resources, and have a much smaller footprint.

Fast startup

Low resource usage

Small image size

Containers are lightweight virtual environments that provide many of the benefits of VMs without the overhead.

4. What is Docker?

Docker is a popular implementation of Linux containers that offers a simple interface for building, distributing, and running container images. It packages an application and all its dependencies into a single image that can run consistently on any host.

5. Common Docker use cases

One‑off environments for testing or CI pipelines.

Elastic cloud services that can be started and stopped on demand.

Micro‑service architectures where multiple containers run on a single host.

6. Installing Docker

Docker provides a Community Edition (CE) and an Enterprise Edition (EE). For most developers, CE is sufficient. Installation instructions are available on the official Docker documentation site.

Mac: https://docs.docker.com/docker-for-mac/install/

Windows: https://docs.docker.com/docker-for-windows/install/

Ubuntu: https://docs.docker.com/install/linux/docker-ce/ubuntu/

Debian: https://docs.docker.com/install/linux/docker-ce/debian/

CentOS: https://docs.docker.com/install/linux/docker-ce/centos/

Fedora: https://docs.docker.com/install/linux/docker-ce/fedora/

Other Linux distributions: https://docs.docker.com/install/linux/docker-ce/binaries/

After installation, verify with: $ docker version If you need to run Docker without sudo each time, add your user to the docker group: $ sudo usermod -aG docker $USER Start the Docker daemon if it is not running:

$ sudo service docker start

$ sudo systemctl start docker

7. Images and containers

An image is a read‑only template that contains an application and its dependencies. Docker creates a container (a writable instance) from an image. Multiple containers can be launched from the same image.

Typical image commands:

# List images
$ docker image ls
# Remove an image
$ docker image rm [imageName]

Containers also have lifecycle commands:

# List running containers
$ docker container ls
# List all containers (including stopped)
$ docker container ls --all
# Stop a container
$ docker container kill [containerID]
# Remove a container file
$ docker container rm [containerID]

8. Hello‑world example

Pull the official hello‑world image and run it:

$ docker image pull hello-world
$ docker container run hello-world

The container prints a confirmation message and then exits.

9. Writing a Dockerfile

A Dockerfile defines how to build an image. Example for a Node.js Koa demo:

FROM node:8.4
COPY . /app
WORKDIR /app
RUN npm install --registry=https://registry.npm.taobao.org
EXPOSE 3000
CMD node demos/01.js

Explanation of each line:

FROM – base image (Node 8.4).

COPY – copy source files into the image, respecting .dockerignore.

WORKDIR – set working directory.

RUN – install dependencies during build.

EXPOSE – declare the container’s listening port.

CMD – default command executed when the container starts.

10. Building and running the custom image

Build the image with a tag: $ docker image build -t koa-demo . Run a container from the image, mapping host port 8000 to container port 3000:

$ docker container run -p 8000:3000 -it koa-demo /bin/bash

Or let the CMD start the app automatically:

$ docker container run --rm -p 8000:3000 -it koa-demo

11. Managing containers

Start a stopped container: $ docker container start [containerID] Stop a container gracefully (SIGTERM) or forcefully (SIGKILL):

$ docker container stop [containerID]
$ docker container kill [containerID]

View logs: $ docker container logs [containerID] Execute a command inside a running container:

$ docker container exec -it [containerID] /bin/bash

Copy files from a container to the host:

$ docker container cp [containerID]:/path/to/file .

12. Publishing an image

Log in to Docker Hub, tag the image with your repository name, and push it:

$ docker login
$ docker image tag koa-demo username/koa-demo:1.0
$ docker image push username/koa-demo:1.0

After a successful push, the image appears in your Docker Hub repository and can be pulled by others.

13. Additional useful commands

docker container start

– restart an existing stopped container. docker container stop – send SIGTERM (and later SIGKILL) to stop a container. docker container logs – view a container’s stdout/stderr. docker container exec – run a command inside a running container. docker container cp – copy files between host and container.

These commands cover the most common Docker workflows for development, testing, and deployment.