Why Docker

Problem (before containers)

• lots of individual machines or VMs
• hard to maintain the machines
• have to install application code on machines

Solution (Docker to the rescue)

Docker bundle all the application code, support binaries, and configuration together and pull them in image (only do once).

• build image: consistently package everything out
• ship image: easily ship these images to where you want
• run image: easily and consistently execute the applications
• CI/CD: being able to run the applications easily and test them in different environments
• different versions: easily run different versions of application without installing
• roll forward: when a defect is found, developers are able to fix it and deploy that new fix (don't have to pull it back)

Docker vs. VM

Docker

• have tiny containers run on the machine
• containers share a kernal

VM

• each VM has its own operating system (has their own kernal)
• running apps on those operating system

Basic Commands

Manage containers

Run a command in a new container

$ docker container run -it -p [local machine port]:[container exposed port] [image]
$ docker container run -d -p [local machine port]:[container exposed port] --name [NAME] [image]

• -it: interactive mode (run in the foreground)
• -d: detached (run in the background)

List containers

$ docker container ls
$ docker container ls -a

// a shorter way
$ docker ps
$ docker ps -a

• -a: all

Remove one or more containers

$ docker container rm [CONTAINER ID]

// remove a running container
$ docker container rm [CONTAINER ID] -f
$ docker rm $(docker ps -aq) -f

• -f: force

Stop one or more running containers

$ docker container stop [CONTAINER ID]

Manage images

List images

$ docker images

Remove one or more images

$ docker image rm [IMAGE ID]

Pull an image or a repository from a registry

$ docker pull [image]

Run a command in a running container

$ docker container exec -it [NAME] bash

Writing Dockerfile

以 Python 為例

FROM python:3.8-slim-buster

WORKDIR /app

ENV PORT 8080

COPY requirements.txt requirements.txt

RUN pip3 install -r requirements.txt

COPY . .

CMD [ "python3", "main.py" ]

以 Node.js 為例

FROM node:17.0.1-alpine

WORKDIR /app

COPY . .

RUN npm i

EXPOSE 3000

CMD ["npm", "run", "start"]

• FROM: Set the baseImage to use for subsequent instructions. FROM must be the first instruction in a Dockerfile.
• WORKDIR: Set the working directory
• ENV: Set the environment variable key to the value.
• COPY: Copy files or folders from source to the dest path in the image's filesystem.
• RUN: Execute any commands on top of the current image as a new layer and commit the results.
• EXPOSE: Define the network ports that this container will listen on at runtime.
• CMD: Provide defaults for an executing container.

Reference

• https://www.youtube.com/watch?v=iqqDU2crIEQ&t=506s
• https://www.youtube.com/watch?v=Kyx2PsuwomE
• https://docs.docker.com/language/python/build-images/
• https://blog.wuhsun.com/learn-how-to-use-cloud-build-deploy-service-to-gke/