Dockerize It!

A guide for Docker along with examples of Dockerfiles and Docker-compose files.

Docker Commands

View Containers

docker container ls

docker ps

Flags:

-a = show all containers

-q = show all active container ids

-ql = show last active container id

-qa = all container ids

docker start $(docker ps -ql)

docker ps -qa | xargs docker stop

Inspect Container

docker inspect container_id || container_name 

Start Container

docker start container_id || container_name 

Stop Container

docker stop container_id || container_name

Delete Container

docker rm container_id || container_name

Delete all:

docker ps -qa | xargs docker rm -f

Create Container

docker run base_image_name:tag_name + args_for_ENTRYPOINT --name name_container

• If no local image found, runs Docker pull to check Docker Hub

-it = shell into the running container

-e = environment variable -e PORT...

--rm removes container after shutdown

Rename Container

docker rename container_id || old_container_name new_container_name

Remove Container

docker rm container_id || container_name 

Get Image

docker pull username/image_name:tag_name

• Default tag name is latest

View Images

docker images

View Image Layers

docker name_of_image:tag_name history

Create Image

Standard

1. Create Dockerfile

Dockerfile:

FROM base_image_name:tag_name
RUN install x && install y
RUN install y
COPY file_name + destination
WORKDIR starting_directory_for_CMD
CMD npm start
ENTRYPOINT ["command", "command", "command"]
MAINTAINER author_name + author_email
EXPOSE port_number
ENV environment_var
USER command_line_user

• RUN installs, commands end after execution always put before COPY src

• CMD only executed once per Dockerfile as default command

• ENTRYPOINT allows for args to be passed in via terminal with docker run to be executed by ENTRYPOINT overriding a potentially a default CMD

• COPY copies directories recursively. All files in the root directory can be selected with . The root directory of the build starts with / for the destination. best practice is . /src/

• VOLUME directory to hold persistent data

• WORKDIR sets directory for run commands, instead of cd directory_name

• ENV can be injected on docker run with -e

• USER default is root user

2. Build Image

docker build -t name_of_image:tag_name + Dockerfile_location

Flags:

-q with build = limits output

--no-cache = build from scratch

Share Image

docker push username/image_name:tag_name

Delete Image

docker rmi container_id || container_name

Connect to Container

-In order to connect to a container you must publish the exposed ports

• You can do this with the -P flag during container creation then run docker ps to find the port mapping

• Or you can manually map the port to connect with it using -p exposed_port:container_port

• bridge network (same computer) is the default

• --net none is null network driver

• overlay network (multiple computers)

• can use --net to connect new container to existing network

• can use same container_name if different networks using --net-alias

View Networks

docker network ls

Mount Volume

docker run -v host_location:container_location

Connect Container to Container

A. Default Network

• docker-compose finds all child Dockerfiles to run multiple containers in default bridge network

docker-compose.yaml:

service_name: 
  build: src_directory
  image:
  ports:
  networks:
  volumes:
  environment:
  command:

-build can be written as
      build:
        context: ../../jenkins/docker

B. Define Your Own

version: "3"
services:
  postgres:
    container_name: class_postgres_4
    image: postgres:11.1
    restart: unless-stopped
    networks:
      - my-net
    ports:
      - "15432:5432"
    environment:
      POSTGRES_USER: "postgres"
      POSTGRES_PASSWORD: "${MY_PG_PASS}"
      POSTGRES_DB: "gogs"
    healthcheck:
      test: ["CMD", "pg_isready", "-U", "postgres", "-d", "gogs"]
      interval: 10s
      timeout: 5s
      retries: 5

Defining the network via docker-compose:

networks:
  my-net:
    driver: bridge

C. CLI Option

docker network ls

docker network create network_name 

docker run --net network_name 

Docker Compose CLI

docker-compose ps

docker-compose up -d

docker-compose down

docker-compose kill

docker-compose rm

docker-compose build

View Volumes

docker volume ls

Orchestration Tools

• New Relic’s Centurion
• Spotify’s Helios
• Ansible’s Docker

Distributed Schedulers

• Google’s Kubernetes
• Apache Mesos

Cloud Providers

• Amazon EC2 Container Service
• Google Container Engine
• Red Hat OpenShift 3
• Joyent Triton
• Microsoft Azure