Comprehensive Docker and Containerization Guide: Concepts, Installation, Commands, Images, Networking, Compose, and Registry

This article introduces Linux containers as isolated process groups and explains how they differ from traditional virtualization by sharing the host kernel while providing portable, consistent environments for applications.

It reviews the evolution of container technology from FreeBSD jails to LXC and Docker, highlighting Docker's role in simplifying container creation, distribution, and management.

Docker installation and basic usage : step‑by‑step commands to install Docker on CentOS, configure the daemon, and verify the version. Essential commands such as docker run , docker start , docker stop , docker ps , docker exec , and container inspection are demonstrated with examples.

Image management : pulling images, listing local images, tagging, exporting, importing, and removing images using commands like docker pull , docker images , docker tag , docker save , docker load , and docker rmi . The article also shows how to commit a running container to a new image with docker commit .

Dockerfile basics : explanation of Dockerfile directives (FROM, RUN, CMD, EXPOSE, VOLUME, etc.) with a sample file that installs SSH on a CentOS base image and sets the default command. Instructions for building an image with docker build -t myimage . are provided.

Image layering : description of how Docker images are built as read‑only layers stacked on a writable container layer, enabling resource sharing and copy‑on‑write semantics.

Docker Compose : creating a docker-compose.yml file to define multi‑container applications (e.g., WordPress with MySQL), using docker-compose up and scaling services with docker-compose up --scale . Example includes networking and volume configuration.

Networking : overview of Docker network drivers (bridge, host, none, container, macvlan, overlay) and practical commands for creating custom bridge networks, linking containers, and inspecting network settings. The guide also covers using pipework and socat for advanced network manipulation.

Private registry : steps to run a local Docker registry, configure insecure registries, tag images, and push/pull images. It also explains adding basic authentication with htpasswd and securing the registry.

Harbor deployment : instructions to install the Harbor enterprise registry using Docker Compose, configure admin credentials, and push images to a Harbor project.

Best practices : recommendations such as avoiding large monolithic images, running processes as non‑root, not using the latest tag, storing data outside containers, and enabling automatic restart policies.

Monitoring : brief mention of container metrics (CPU, memory, I/O, network) and tools for observing container health.