What Does It Really Cost to Master Docker? Deep Dive into Architecture & Storage

Why is Docker So Popular?

Docker’s rise mirrors the container shipping revolution: just as standardized containers transformed global logistics by boosting loading efficiency and reducing damage, Docker standardizes application packaging, making deployment faster and more reliable.

Benefits of Containers

Save labor and reduce transportation costs

Minimize cargo loss and damage, ensuring quality

High loading and unloading efficiency

Standardized specifications simplify transport

What Docker Brings to Enterprises

Docker leverages Linux kernel namespaces and cgroups, offering several advantages:

Improved development and testing efficiency; environments are easy to reproduce.

Facilitates DevOps practices.

Image‑based delivery ensures consistent environments.

Enhanced collaboration among development, testing, and operations.

Build once, run anywhere.

Docker Architecture

Docker follows a client‑server model:

The Docker client runs commands such as docker images or docker ps.

The Docker daemon processes those commands on the host.

Understanding this C/S architecture is sufficient for most operations staff.

Dockerfile, Image, and Container Relationship

The workflow typically looks like this:

Pull a base image (e.g., centos) from Docker Hub.

Create a Dockerfile that builds a new image on top of the base.

Run docker build to generate the image.

Start a container with docker run.

Manage the container using docker start, docker stop, docker restart, docker rm, etc.

Optionally commit a running container back to an image.

Push the custom image to a registry for sharing.

Docker Storage Drivers

Docker storage consists of two aspects: container/image storage and file‑data storage. The supported storage drivers are:

AUFS (Another Union File System)

Overlay

Devicemapper

All images are built with a copy‑on‑write (CoW) layered filesystem. AUFS merges multiple directories into a single virtual view. Overlay creates a lower (read‑only) layer and an upper (read‑write) layer, requiring kernel 3.18+. Devicemapper maps logical devices to physical block devices, offering fine‑grained CoW at the block level.

Overlay Example

mount -t overlay overlay -olowerdir=/lower,upperdir=/upper,workdir=/work /merged

Limitations and Docker Volumes

While layered images save space and speed distribution, they have drawbacks:

Data inside a container cannot be directly accessed from the host.

Containers cannot share data with each other by default.

Data disappears when the container is removed.

Docker volumes, built on the VFS filesystem, address these issues by providing persistent, shareable storage that remains after container deletion and can be mounted across multiple containers.

Summary: Costs of Using Docker

Operations staff must become proficient with Docker commands.

Operations need to write and maintain Dockerfiles.

Development and operations must collaborate to create images.

Testing teams only need basic Docker knowledge.

Projects should include a Dockerfile and .dockerignore in the source repository.

Docker is best suited for web‑based or microservice applications.