Docker Introduction

Nathan Luong | April 15, 2024 10

Glossary

Image vs Container

ImageContainer
Docker imageDocker Container
The Actual PackageActually start the application
The artifact that can be moved aroundThe Container is a running environment for Image
Images usually form layers
For example postgres Image is built on top of base alpine

📝

This is new Data

All data will be lost when a container is destroyed. Need to use volume to persist data

Ports

Container Port needs to be bind onto a port of the host Port Binding

Commands

Docker Run

Create and run a new container

  • docker run redis: Starts the Redis image in container
  • docker run -p 6000:6379 redis: Bind Redis container port 6379 onto port 6000 of host
  • docker run -d -p 6000:6794 redis: Run Redis on port 6000 in detach mode
  • docker run -d -p 6000:6794 redis --name redis-two redis: Run Redis image on port 6000 in detach mode, with the container name of redis-two instead of the container ID

Docker Exec

  • docker exec -it redis-two /bin/bash: Launch the interactive terminal with bash inside of the container
  • exit: Exit the docker terminal

Docker Run

## create docker network
docker network create mongo-network

### start mongodb
docker run -d \ 
-p 27017:27017 \
-e MONGO_INITDB_ROOT_USERNAME=admin \
-e MONGO_INITDB_ROOT_PASSWORD=password \
--net mongo-network \
--name mongodb \
mongo

### start mongo-express
docker run -d \
-p 8081:8081 \
-e MONGO_INITDB_ROOT_USERNAME=admin \
-e MONGO_INITDB_ROOT_PASSWORD=password \
--net mongo-network \
--name mongo-express \
mongo-express
  • Can be created all at once with Docker Compose and yaml file

General

  • docker pull redis : Pulls the latest Docker Images of Redis from Docker Hub

  • docker pull redis:123: Pull Redis version 123

  • docker start <containerID>: Start the container

  • docker stop <containerID>: Stop the container

  • docker logs <cid>: print the logs of the container

  • docker images: Show all Docker images

  • docker ps: List all running Docker container

  • docker ps -a: List all Docker container running and not running

  • docker network create mongo-network: Create a new network called mongo-network

  • docker network ls: List all docker networks

  • docker build -t my-app:1.0 .: Build a Docker Image call my-app with the Dockerfile located in the current directory

Docker Workflow

Simple Workflow

Jenkins Pipeline
  • Developing the application
  • Push to GitHub
  • Jenkins pickup the code and build the Docker Image
  • The Docker pushed to a private Docker Repository
  • The Docker Image got deployed onto a dev server
  • Tester can test the app on Dev Server

Dockerfile

  • A blueprint for building docker image
## Install node
FROM node

## Set the environment variable
ENV MONGO_DB_USERNAME=admion \
	MONGO_DB_PWD=password

## Execute any linux command with RUN
## Create a directory name home/app in the Docker Container
## We can have multiple run commands but only one CMD
RUN mkdir -p /home/app

## Copy a file from the host into the docker container
COPY . /home/app

## Entry Linux command to run in the container
## Start the app with "node server.js"
CMD ["node", "server.js"]

FROM alpline:3.10

ENV NODE_VERSION 13.1.0

RUN ...

COPY docker-entrypoint.sh /usr/local/bin/
ENTRYPOINT ["docker-entrypoint.sh"]

CMD ["node"]

RUN vs CMD

  • RUN can execute any Linux commands and there can be multiple RUN commands
  • CMD is an entry command which every container can only have 1 of

Docker Volumes

Problems

  • Containers runs on host and have a virtual file system
  • The data will be gone when the container got destroyed, restarted

Solutions

  • Create a physical file system on the host machine
  • Folder in physical host file is mounted into the virtual file system of Docker
  • The data that is in the Virtual File System will be duplicated on the Host File System

3 Volume Types

Host Volume

  • Developer decide which folder from the host to get mounted onto the container
## Mount host /home/mount/data onto virtual /var/lib/mysql/data
docker run -v /home/mount/data:/var/lib/mysql/data

Anonymous Volumes

  • For each container a folder is generated that gets mounted
## Pass in the container folder path, 
## the volumes on the host is automatiacally generated
docker run -v /var/lib/mysql/data

Named Volumes

  • For each container a folder on host is generated that gets mounted
  • The folder will be named whatever, for example lmao
  • The volume can be referenced by its name

📝

Share Data

  • A volume, with the same reference can be mounted on multiple containers if they need to share data.

🎉

Should be used in production

  • There are benefits for Docker to manage the Volumes for developers.
  • These Names can be reference inside a Docker Compose file
## Pass in the container folder path, 
## the volumes on the host is automatiacally generated
docker run -v lmao:/var/lib/mysql/data