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赵文博
赵文博

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Docker Feature Overview

#docker #devops #tutorial #beginners

Basic Concepts

1) Container

A container is like a lightweight box that bundles everything an application needs to run.

  • Application code
  • Runtime (for example Java or Python)
  • Dependency libraries
  • Basic system tools

Compared with virtual machines, containers do not carry the overhead of a full guest operating system. They are smaller, start faster, and typically use resources more efficiently.

2) Image

An image is the template or blueprint used to create containers.

  • It is essentially a snapshot of a filesystem plus some metadata and configuration.
  • Images are built in layers.
  • When you run docker run <image>, Docker creates a container from that image and adds a writable layer on top.

3) Registry

A registry is where images are stored and distributed. Think of it as an “image warehouse”.

  • Public registries: Docker Hub, Aliyun Container Registry, and others.
  • Private registries: company-hosted registries for internal images.

Common operations:

  • Pull an image: docker pull <registry>/<image>:<tag>
  • Push an image: docker push <registry>/<image>:<tag>

How containers, images, and registries relate

Common Commands 

# 1) Image management
docker images                     # list local images
docker pull nginx:latest          # pull an image from a registry
docker rmi nginx:latest           # remove a local image

# 2) Container management
docker run -d --name web nginx    # start an nginx container named "web" in background
docker ps                         # list running containers
docker ps -a                      # list all containers (including stopped ones)
docker stop web                   # stop the "web" container
docker start web                  # start a stopped container
docker rm web                     # remove a stopped container

# 3) Build an image
docker build -t myapp:1.0 .       # build an image from Dockerfile in current directory

# 4) Logs and monitoring
docker logs web                   # view container logs
docker stats web                  # realtime resource usage
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Docker Networking

Docker creates several default networks:

  • bridge: default network (NAT + virtual bridge)
  • host: container shares the host network stack
  • none: no networking

Common commands:

# List networks
docker network ls

# Inspect a network
docker network inspect bridge

# Create a custom bridge network
docker network create --driver bridge my-net

# Start a container and attach it to the custom network
docker run -d --name db --network my-net mysql

# Connect an already-running container to a network
docker network connect my-net web

# Disconnect a container from a network
docker network disconnect my-net web
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Why custom networks are useful:

  • Containers on the same user-defined network can reach each other by container name.
  • Better isolation between environments and services.

Inspecting Container Details

When you need detailed container configuration (port mappings, volumes, environment variables, etc.), use:

docker inspect web
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The output is JSON. Useful fields include:

  • HostConfig.PortBindings: port mappings
  • Mounts: volume mounts
  • Config.Env: environment variables
  • NetworkSettings: networking

If you only want specific parts, combine with jq (or simple grep):

# Only port bindings
docker inspect web | jq '.[0].HostConfig.PortBindings'

# Only mounts
docker inspect web | jq '.[0].Mounts'
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Tips

  • Layered images: every Dockerfile change usually creates a new layer. Layer caching makes builds faster.
  • Data persistence: in production, mount databases and logs to the host using volumes so data is not lost when containers are recreated.
  • Environment isolation: custom networks + private registries help isolate dev, test, and prod environments more cleanly.

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