May 04, 2020

Docker Basics Study Logs Part 1.

This is my study logs, while taking the docker mastery course on Udemy.

It basically covers fundamental of containers, images, and the use of docker compose.

Create and Use Containers

docker version
# verified cli can talk to engine

docker info
# most config values of engine
docker <command> <sub-command>
docker container run --publish --detach 80:80 nginx
  1. Download image nginx from Docker Hu
  2. Started a new container from that image
  3. Opened port 80 on the host IP
  4. Routes that traffic to the container IP, port 80

--detach will make it run on the background.

docker container ls

docker container stop ea

docker container ls -a
# Container are created on every container run

docker container run --publish --detach 80:80 nginx
# with names

docker container logs webhost
# Checks logs

docker container top webhost
# Check the process of the container

docker container rm -f webhost
# Remove running container
  • Behind docker container run
docker container run --publish 8080:80 --name webhost -d nginx:1.11 nginx -T
  1. Looks for that image locally in image cache
  2. Looks in remote image repository (defaults to Docker Hub)
  3. Download the latest version (nginx:latest by default)
  4. Creates a new container based on that image and prepares to start
  5. Gives it a virtual IP on a private network inside docker engine
  6. Opens up port 80 on host and forward to port 80 in container
  7. Starts container by using CMD in the image Dockerfile
  8. Containers are just process
  9. Creating 3 different containers
docker container run --name nginx --publish 80:80  --detach nginx
docker container run --name httpd --publish 8080:80 --detach httpd
docker container run --name mysql --publish 3306:3306 --env MYSQL_RANDOM_ROOT_PASSWORD=yes --detach mysql

docker container logs mysql
# to check the generated root password
  • What's going on the container
docker container top  <container_id>
# list proces in one container

docker container inspect <container_ID>
# Gets JSON detail of one container

docker container stats
# Can check all the running container, and make sure to check THE CPU, and memory
  • Getting a shell inside container
docker container run -it --name proxy nginx bash

docker container start -ai proxy
# start again, for stopped containers

docker container exec -it mysql bash
# creates additional process, and jump it to the shell for running container
  • Network

Virtual Network can have multiple containers, can communicate together.

docker container port <container>
# Quick port check
docker network ls
# show network

docker network inspect <network>
# inspect network, and which containers are inside this network

docker network create my_app_net

docker network connect/disconnect
# connect/disconnect current containers
  • DNS

The container name works as a host name of the container, so if two containers are in the same virtual network, you can ping each other.

But this needs to be using the default bridge network drive, allowing containers to communicate with each other when running on the same docker host.

docker container run -d --name new_nginx --network my_app_net nginx
# specifying network when running container

docker network inspect my_app_net
  • Emulate DNS Round Robin
docker network create search_net

docker container run -d --name search1 --network search_net --network-alias search elasticsearch:2
docker container run -d --name search2 --network search_net --network-alias search elasticsearch:2

docker container run --rm --net search_net alpine nslookup search
# Server:         127.0.0.11
# Address:        127.0.0.11:53
#
# Non-authoritative answer:
#
# Non-authoritative answer:
# Name:   search
# Address: 172.20.0.3
# Name:   search
# Address: 172.20.0.2

docker container run -it --name centos --net search_net centos
# Check if the response of the elasticsearch has different two different names, when you request couple of times

Docker Image

  • Consider small OS like alphine
  • Layered
docker image history <image>
docker image inspect <image>
  • Tags
docker image tag nginx kawamurakazushi/nginx
docker image push kawmaurakazushi/nginx

docker image tag kawamurakazushi/nginx kawamurakazushi/nginx:testing
  • Building from Dockerfile
FROM
ENV
# set environment variable
WORKDIR
# bascially change directory
COPY
# copy from local
CMD

You should put the commands that change the least on the top, and the command that changet most on the bottom, since it caches from the top.

docker image build customnginx .
  • if you don't specify CMD, it will inherit from the image from FROM.
docker image build -t nginx-with-html .
docker container run -p 80:80 --rm nginx-with-html
  • Cleaning up images and systems
docker image prune
docker system prune
# Delete everything that is not running

docker system prune -a
# Delete everything that is not used

docker system df
# Check the disk usaage

Container Lifetime & Persistent Data

  • Volumes => make special location outside of container UFS
  • Bind Mounts => link container path to host path
  • VOLUME will create a persistent data.

This will be never removed, when the container is removed.

docker volume ls
# DRIVER              VOLUME NAME
# local               2fa2e747189d574821f59592e541822c1c96485e93d8640a8ee57b366b6c45fc
# local               3b385d7fa684c1664b37ac4eb025f8d8edb97b3ed95266f4a67462627b46d1ae
# local               3d49b042e6f5279fe27ee21d99698f3ef41fedecec88bbf01f87895f9c3c9c62
# ...

But it's quite hard to keep track, without the names.

docker container run -d --name mysql -e ALLOW_EMPTY_PASSWORD=true -v mysql-db:/var/lib/mysql mysql
docker volume ls
# DRIVER              VOLUME NAME
# local               2fa2e747189d574821f59592e541822c1c96485e93d8640a8ee57b366b6c45fc
# local               mysql-db

docker volume inspect mysql-db
# [
#     {
#         "CreatedAt": "2020-05-05T03:22:58Z",
#         "Driver": "local",
#         "Labels": null,
#         "Mountpoint": "/var/lib/docker/volumes/mysql-db/_data",
#         "Name": "mysql-db",
#         "Options": null,
#         "Scope": "local"
#     }
# ]
  • Bind Mounting

Maps a host file or directory to a container file or directory. Can't be used in a Dockerfile, and should be specified on container run

d container run -d --name nginx -p 80:80 -v $(pwd):/usr/share/nginx/html nginx

Docker Compose

  • Configure relationship between containers
  • Save our docker container run settings in easy-to-read files
  • Create one-liner developer environment start up
docker-compose up
docker-compose down
  • Example for drupal configuration with posgres
version: "3"
services:
  drupal:
    image: "drupal"
    ports:
      - 8080:80
  psql:
    image: "postgres:11"
    environment:
      POSTGRES_DB: drupal
      POSTGRES_USER: user
      POSTGRES_PASSWORD: pass
  • Building from specific Dockerfile
version: "2"
services:
  proxy:
    build:
      context: .
      dockerfile: nginx.Dockerfile
    ports:
      - "80:80"
  web:
    image: httpd
    volumes:
      - ./html:/usr/local/apache2/htdocs/
  • If you change something on your Dockerfile, you need to specify --build option, to build from Dockerfile again.
docker-compose up --build
Written by...
Kazushi Kawamura
Software Engineer based in Tokyo.
2019 © Kazushi Kawamura.