Introduction to Docker and Its Ecosystem

Docker is an open‑source tool originally created by DotCloud that packages any application into a Linux container. First released in March 2013, the latest version mentioned is 1.3. It is written in Go, hosted on GitHub, and has accumulated more than 10,000 commits. Docker provides lightweight isolation, automatic packaging and deployment, and can be used to build a private PaaS cloud, development‑test environments, or scalable web applications.

Docker vs. Virtual Machine

Unlike a VM, which runs a full guest operating system and consumes considerable CPU, memory and disk resources, Docker only contains the application and its dependent libraries. It runs on the host via libcontainer, making it much lighter and faster (containers start within seconds). However, Docker’s isolation is weaker than a VM’s, its networking is simple (bridge‑based by default), and log inspection is less flexible.

Docker Components

Docker daemon – the background service running on the host; users interact with it through the Docker client.

Docker client – the command‑line tool that communicates with the daemon via socket or RESTful API.

Docker hub/registry – stores and shares images (e.g., https://registry.hub.docker.com/ ), with the option to run a private registry.

Two core concepts:

Docker image – a read‑only template containing the files needed to run a container; images can be built with a Dockerfile or pulled from a registry.

Docker container – a running instance of an image, providing an isolated environment where multiple containers do not interfere with each other.

Docker Networking

The default networking mode is bridge. When Docker starts, it creates a virtual Ethernet bridge docker0 on the host. Each container gets a paired virtual interface (e.g., veth****) that is attached to docker0, allowing containers to communicate with the host and each other. The container’s default gateway is the IP address of docker0.

Other networking modes include host, container, and none, selected with the --net flag, e.g.: docker run -i -t --net=host ubuntu /bin/bash The host mode lets a container share the host’s network stack, improving performance but reducing isolation. container mode shares another container’s network namespace, while none disables networking entirely.

Basic Docker Commands

Installation is described in the official documentation. Common commands include: docker version – show Docker version. docker info – display system information. docker images – list local images (stored under /var/lib/docker). docker pull ubuntu:latest – download an image from Docker Hub. docker run -i -t ubuntu /bin/bash – start a container. docker run -i -t --rm ubuntu /bin/bash – start a container that is removed automatically after exit. docker run -t -i --name test_container ubuntu /bin/bash – assign a name to the container. docker run -t -i --net=host ubuntu /bin/bash – use host networking. docker run -t -i -v /host:/container ubuntu /bin/bash – bind‑mount a volume. docker ps – list running containers. docker stop <container_id> – stop a container.

docker commit -m="test docker commit" <container_id> <new_image_name>

– create a new image from a container’s changes.

Building Images with Dockerfile

Example Dockerfile for a Django application:

FROM ubuntu:12.04
MAINTAINER Your Name
RUN apt-get update
RUN apt-get install -y python-software-properties python-pip
ADD myproject /opt/code
RUN pip install -r /opt/code/requirement.txt

Build the image with: docker build -t docker_test . Run the container:

docker run -i -t docker_test /bin/bash -c "cd /opt/code; python manage.py runserver 0.0.0.0:8080"

Push the image to a private registry:

docker tag test docker.example.com/test

docker push docker.example.com/test

Remove unused images or containers with docker rm and docker rmi.

Docker Ecosystem

Docker’s rapid adoption has spawned a rich ecosystem. Notable projects include:

CoreOS – a lightweight Linux distribution designed for large‑scale container deployment, featuring etcd for service discovery and Fleet for container orchestration.

Kubernetes – Google’s open‑source system for managing container clusters, providing pods, replication controllers, services, and a master‑minion architecture.

Deis – a PaaS built on Docker and CoreOS, inspired by the Twelve‑Factor App methodology, handling build, release, and run stages.

Flynn – similar to Deis, with a layered architecture (layer0 for resource scheduling and discovery, layer1 for application management) that runs applications inside Docker containers.

Conclusion

Since its first release in 2013, Docker has become globally popular, with frequent updates and an expanding set of complementary tools. While Docker’s lightweight containers simplify deployment and scaling, rapid version changes can cause compatibility issues, and many surrounding tools are still in early development stages. Nevertheless, Docker’s ability to run anywhere and isolate resources makes it a compelling choice for modern software delivery.

References:

https://docs.docker.com/articles/

https://docker.cn/

http://domino.research.ibm.com/library/cyberdig.nsf/papers/0929052195DD819C85257D2300681E7B/$File/rc25482.pdf

http://www.infoq.com/

https://github.com/docker/docker-registry

http://www.xmind.net/m/RHSz/