Comprehensive Docker Guide: Concepts, Installation, Management, and Practical Use Cases

1. What is Docker?

Docker is an open‑source container engine written in Go, allowing lightweight, portable, and isolated application environments on a host system.

2. Docker Use Cases

Automated packaging and release of web applications.

Continuous integration and testing.

Deploying databases and backend services.

Building private PaaS platforms.

It is especially useful for internal development environments, reducing resource waste compared to virtual machines.

3. Advantages of Docker

Flexibility: complex applications can be containerized.

Lightweight: containers share the host kernel.

Portability: build locally, deploy to cloud, run anywhere.

Scalability: easily increase container replicas.

Stackability: vertical and immediate service stacking.

4. Docker vs. Virtual Machines

VMs add a hypervisor layer and emulate hardware, each with its own kernel, while Docker uses namespaces and cgroups to isolate resources, resulting in lower overhead but slightly weaker isolation.

5. Core Components

Image

Read‑only templates that contain everything needed to run a container.

Container

Runtime instances created from images, isolated from each other.

Registry

Servers that store multiple images; public registry is Docker Hub ( https://hub.docker.com ), with many private options.

6. Quick Installation

Run the following commands to install Docker on CentOS:

yum install -y yum-utils device-mapper-persistent-data lvm2
sudo yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
[root@centos7 ~] yum -y install docker-ce docker-ce-cli containerd.io
# docker ps -- view Docker

[root@centos7 ~]# systemctl enable docker
[root@centos7 ~]# systemctl start docker
[root@centos7 ~]# systemctl status docker
[root@centos7 ~]# docker ps -- view containers
[root@centos7 ~]# docker version
[root@centos7 ~]# docker info

7. Changing Docker Storage Location

Default location: /var/lib/docker . Check with docker info | grep "Docker Root Dir" .

To move:

systemctl stop docker
mkdir -p /root/data/docker
mv /var/lib/docker /root/data/docker
ln -s /root/data/docker /var/lib/docker

8. Image Management

Search Images

Use docker search <keyword> .

Pull Images

Use docker pull repository[:tag] ; default tag is latest .

Inspect Images

Image details are stored under /var/lib/docker . Key fields: REPOSITORY, TAG, IMAGE ID, CREATED, SIZE.

Tag and Delete Images

Tag: docker tag name:tag . Delete: docker rmi repository:tag or docker rmi IMAGE_ID [-f] .

Save and Load Images

Save: docker save -o filename.tar image . Load: docker load -i filename.tar .

9. Creating Containers

#docker images   -- list images
docker run -d --name centos7.8 -h centos7.8 \
  -p 220:22 -p 3387:3389 \
  --privileged=true \
  centos:7.8.2003 /usr/sbin/init

# Create a Linux 8.2 environment
docker run -d --name centos8.2 -h centos8.2 \
  -p 230:22 -p 3386:3389 \
  --privileged=true \
  daocloud.io/library/centos:8.2.2004 init

# Enter container
docker exec -it centos7.8 bash
docker exec -it centos8.2 bash
cat /etc/redhat-release   -- view OS version

10. Docker Run Process

Check for local image; pull if missing.

Create and start a container from the image.

Mount a writable layer over the read‑only image.

Bridge a virtual network interface to the container.

Assign an IP address from the pool.

Execute the specified application; container stops when it exits.

11. Docker Network Modes

host

Use --net=host ; container shares the host’s network namespace.

container

Use --net=container:NAME_or_ID ; shares another container’s network namespace.

none

Use --net=none ; container gets no network interfaces.

bridge

Default mode; creates an isolated network namespace, connects to docker0 bridge, and sets up NAT with iptables.

12. Docker Data Volumes

Special directories inside containers that can be mounted from the host, allowing persistent data without affecting the image.

13. Setting Up a Private Registry

# Pull registry image
docker pull registry
# Run registry container
docker run -di --name registry -p 5000:5000 registry
docker update --restart=always registry   # enable auto‑restart
# Verify
docker ps -a --format "table {{.ID}}	{{.Names}}	{{.Status}}"
# Access URL: http://192.168.1.54:5000/v2/_catalog
# Configure trust
vi /etc/docker/daemon.json
{
  "registry-mirrors": ["https://docker.mirrors.ustc.edu.cn"],
  "insecure-registries": ["192.168.1.54:5000"]
}
systemctl restart docker
# Push an image
docker tag postgres:11 192.168.1.54:5000/postgres
docker push 192.168.1.54:5000/postgres
# Pull it back
docker rmi 192.168.1.54:5000/postgres
docker pull 192.168.1.54:5000/postgres

14. Backup and Migration

Save a container as an image, then export the image:

# Commit container to image
docker commit redis myredis
# Save image to file
docker save -o myredis.tar myredis
# Restore on another host
docker load -i myredis.tar

15. Deploy MySQL with Docker

Download Image

# Pull MySQL images
docker pull mysql:5.7.30
docker pull mysql:8.0.20

Run Containers

mkdir -p /usr/local/mysql5730/
mkdir -p /usr/local/mysql8020/

docker run -d --name mysql5730 -h mysql5730 \
  -p 3309:3306 \
  -v /usr/local/mysql5730/conf:/etc/mysql/conf.d \
  -e MYSQL_ROOT_PASSWORD=root -e TZ=Asia/Shanghai \
  mysql:5.7.30

docker run -d --name mysql8020 -h mysql8020 \
  -p 3310:3306 \
  -v /usr/local/mysql8020/conf:/etc/mysql/conf.d \
  -e MYSQL_ROOT_PASSWORD=root -e TZ=Asia/Shanghai \
  mysql:8.0.20

Access MySQL inside the container:

# Enter container
docker exec -it mysql5730 bash
mysql -uroot -proot
# Remote access
mysql -uroot -proot -h192.168.59.220 -P3309