Master Docker: From Origins to Commands, Networking, and Volumes

Overview

Origin

Docker was open‑sourced in 2013 by DotCloud, a PaaS provider, reflecting its original focus on container management.

Technical Principles

Initially built on LXC, Docker relies on two Linux kernel features:

cgroup : groups processes for unified resource control (CPU, memory, etc.).

namespace : provides each group with isolated PID, IPC, and network spaces.

Pain points addressed

Packaging and deployment.

Standardizing runtime environments.

More efficient utilization of physical machines.

Docker basic commands

Container lifecycle (create, start, stop, restart, remove)

docker pull busybox – download an image.

docker run -it --rm --name busybox busybox – create and run a container.

docker stop/kill busybox – stop or force‑stop a container.

docker start/restart busybox – start or restart a container.

docker rm busybox – remove a container.

Common commands

docker exec – run a command inside a running container.

docker cp – copy files between host and container.

docker inspect – view detailed information about containers or images.

docker stats – display resource usage of containers.

docker events – stream Docker daemon events.

docker logs – view container logs.

docker top – list processes running inside a container.

Docker usage examples (busybox)

Containers are isolated, but interaction with the host or other containers is possible via environment variables, volumes, and networking.

Environment variables

docker run -it --rm -e MY_NAME=wangyubin busybox env

Variables defined on the host can be injected at container start.

Volumes (disk)

docker volume ls          # list volumes
docker volume inspect VOL_NAME   # inspect a specific volume

Files created inside a container do not modify the underlying image.

docker run -it --rm busybox
# touch test.txt
# ls
...

When the container is restarted, the file disappears because it was not stored in a volume.

Mounting a host directory shares files between containers:

docker run -it --rm -v /home/wangyubin/tmp/volume:/share-dir busybox
cd /share-dir
touch test.txt

Another container can mount the same directory and see test.txt.

Networking

By default, a container’s services are reachable only from inside the container.

Expose ports to the host

docker run -it -p 1234:1234 --rm busybox
# nc -l -p 1234

The exposed port appears in docker ps and can be accessed from the host.

Containers on the same network

docker network create test
docker network ls
docker run -it --rm --name test01 --network test busybox
# nc -l -p 1234
docker run -it --rm --name test02 --network test busybox
# nc test01 1234

Containers sharing a user‑defined network can address each other by name; containers on different networks cannot communicate.