Docker

Index

1、What is Docker

Docker is a , akin to VMware and VirtualBox, fundamentally serving the purpose of environment isolation. It facilitates a relative independence among projects, resulting in a clearer hierarchical structure.

2、Docker's Advantages

• Convenient and rapid delivery
• Bundling projects with their environments for robust isolation
• Lower maintenance costs

3、Principles of Utilization

• It is recommended in principle to deploy only one application per container, with inter-application communication occurring through inter-container communication mechanisms.
• When building custom images, it is advised to use the most streamlined base image to reduce image size.
• In cases where multiple containers (services) can be categorized, custom networks are recommended. These containers should be placed within a custom network inaccessible to others.
• For scenarios where multiple containers need to share data, it's preferable to use shared volumes instead of shared containers.

4、Install

• ubuntu
• centos
• windows desktop
• mac desktop
• docker compose

5、The Essence

5-1、Image

• Grounded on the kernel of the host machine, layered for overlay, serving as a packaging tool for software runtime environments and file systems developed on those environments.
• : Static, akin to code that remains idle, merely textual characters awaiting execution; read-only, signifying that during image construction, it's akin to constructing a file system where content remains unaltered until runtime; layered structure: Each image builds upon a foundational image, thereby reconstructed atop this foundational base.
• Our projects or environments are founded on a base image, subsequently enriched with environment setups, project code, and related content.

5-2、Containers

• A container operates at runtime, encompassing all the requisite environments for a project, including the system, code, dependencies, and language settings.
• Containers are isolated from one another through a sandbox mechanism, ensuring that they do not interfere with each other.
• Any modifications to a container—whether adding, deleting, or altering files—occur solely within the container layer. Only the container layer is writable; all underlying image layers remain read-only. This means that changes made within a container do not affect other containers dependent upon the same image.

5-3、Network

The network configurations in Docker are fundamentally categorized into four modes:

• Host: In host mode, when launching a container, it shares the same Network Namespace with the host instead of obtaining an independent one. The container does not create its virtual network card or configure its unique IP; rather, it utilizes the host's IP address and ports.

• Container: This mode involves sharing a Network Namespace between a newly created container and an existing one, granting them shared IP addresses and port ranges within the specified container, as opposed to sharing the host's Network Namespace.

• None: Operating in none mode means the Docker container possesses its individual Network Namespace without any predefined network configurations. This implies the Docker container lacks network interfaces, IP addresses, routing information, requiring manual addition of network interfaces and IP configurations.

• Bridge: The bridge mode, being Docker's default network setting, allocates a distinct Network Namespace for each container, configuring IP addresses, and connects Docker containers on a host to a virtual bridge network.

• overlay2：The overlay network is designed to interconnect Docker containers across different machines, enabling communication between containers on diverse hosts while supporting message encryption.

5-4、Volume

Functionality：

• Data Persistence: Data generated by the container can be retained on disk even after the container is removed.
• Data Sharing: Data can be shared among containers.
• Dynamic Modification: Certain configuration files can be mapped for real-time updates.

The three types of volume mappings.：

1. bind mount

Bind a specified directory in the container to a specified directory on the host machine.

version: "3.5"
services:
  rabbitmq:
    image: rabbitmq:3.8.3-management
    container_name: rabbitmq
    volumes:
      - $PWD/data:/var/lib/rabbitmq
    environment:
      RABBITMQ_DEFAULT_USER: root
      RABBITMQ_DEFAULT_PASS: root
      TZ: Asia/Shanghai
    ports:
      - "5672:5672"
      - "15672:15672"

# docker inspect dddfd27a73a5
"Mounts": [
         {
             "Type": "bind",
             "Source": "/home/www/docker-servers/rabbitmq/data",
             "Destination": "/var/lib/rabbitmq",
             "Mode": "rw",
             "RW": true,
             "Propagation": "rprivate"
         }
     ],

2. volume

Bind a specified directory in the container to a volume path managed by Docker.

version: "3.9"
services:
  frontend:
    image: node:lts
    volumes:
      - myapp:/home/node/app
  backend:
  	image: sss
  	volumes:
  	  - myapp:/home/node/app
volumes:
  myapp:

version: "3.9"
services:
  frontend:
    image: node:lts
    volumes:
      - myapp:/home/node/app
volumes:
  myapp:
    external: true

ls /var/lib/docker/volumes/

3. tmpfs mount

Stored in memory, these are seldom utilized and require no extensive introduction. 😛