Why Docker Is Changing Software Development: A Hands‑On Introduction

Quick Start

Docker began as an internal project at dotCloud.

It is written in Go.

Its goal is a lightweight OS‑level virtualization solution.

Based on Linux containers (LXC) and similar technologies.

Containers start in seconds, far faster than traditional VMs.

High resource utilization allows thousands of containers on a single host.

Docker containers virtualize at the operating‑system level, reusing the host OS instead of emulating hardware.

Containers consume minimal extra system resources, delivering high performance; ten applications require ten VMs but only ten isolated containers with Docker.

Main Advantages

Faster delivery and deployment – containers are the smallest unit.

More efficient kernel‑level virtualization.

Easier migration and scaling.

Simpler management.

Installation

Official installers are available for Mac, Linux, and Windows; follow the documentation.

Kitematic provides a graphical interface for easier Docker usage.

Daemon

Run the Docker daemon with -H to change the binding interface, e.g. sudo /usr/bin/docker -d -H tcp://0.0.0.0:2375. To avoid typing the full command each time, set the environment variable export DOCKER_HOST="tcp://0.0.0.0:2375".

Graphical User Interface

Web management tools such as Shipyard and Portainer can simplify container operations.

Basic Concepts

There are three core concepts:

Image : a read‑only template used to create containers; built on a layered UnionFS structure.

Container : a running instance created from an image, with its own writable layer, isolated processes, filesystem, and network.

Registry : a storage location for images, public (Docker Hub) or private.

What Docker Can Do

Standardize, optimize, and accelerate local development and build processes.

Ensure consistent runtime results across environments.

Create isolated test environments.

Isolation Provided by Docker

Filesystem isolation – each container has its own root filesystem.

Process isolation – containers run in separate process spaces.

Network isolation – separate virtual network interfaces and IP addresses.

Resource isolation – cgroups allocate CPU, memory, etc., per container.

Common Commands

sudo docker info

– view Docker status. docker ps – list running containers (add -a for all, -l for the latest).

Running a Simple Example

Create and run an Ubuntu container:

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

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

Building an Image

Create a directory, add a Dockerfile with:

FROM docker/whalesay:latest
RUN apt-get -y update && apt-get install -y fortunes
CMD /usr/games/fortune -a | cowsay

Build the image:

sudo docker build -t wdx-whale .

Managing Images

List local images:

docker images

Tag and push a custom image:

docker tag 26ac9649d7da wdxtub/wdx-whale:latest
docker login --username=wdxtub [email protected]
docker push wdxtub/wdx-whale

Container Lifecycle

Start: docker run (creates if missing, allocates filesystem, network, and runs the command).

Stop: docker stop <container_id>.

Restart: docker restart <container_id>.

Remove: docker rm <container_id> (add -f for running containers).

Export/Import and Deletion

Export a container:

docker export <container_id> > container.tar

Import as an image:

cat container.tar | sudo docker import - myimage:latest

Save and load images:

docker save -o wdx-local-whale.tar wdxtub/wdx-whale
docker load --input wdx-local-whale.tar

Registries

Registries store images; Docker Hub is public, while private registries can be self‑hosted. Use docker pull to download images and docker push to upload them.

Image layers are managed by UnionFS, enabling incremental changes and efficient storage.