Docker

Introduction

Docker is one of the most common software platforms used to create and run containers.

Do Not Use Docker If

You need a speed boost
If you prioritize security over convenience
If you develop desktop GUI applications
If you want to facilitate development
If you need to use different OSs or kernels
If you have a lot of valuable data to store
If you are looking for an easily managed technology

Commands

Container Management

docker create image - Create container from image
docker run image - Create container from image = create + start
docker start container - Start container
docker stop container - Stop container (gracefully)*
- * send SIGTERM signal to main process + SIGKILL after 10 seconds
docker kill container - Kill (SIGKILL) container (forcefully)
docker restart container - = stop + start
docker pause container - Suspend the container
docker unpause container - Resume the container
docker rm [ -f ] container - Remove container
- -f - force remove running container = docker kill + docker rm

Container Inspection

docker ps - List running containers
docker ps -a - List all containers
docker logs [ -f ] container - Get container logs (stdout and stderr)
- -f - follow logs
docker top container [ps options] - List processes running inside container
docker diff container - Show the differences with the image (modified files)
docker inspect container - Show low-level infos (in JSON format)

Interacting with Container

docker attach container - Attach to running container (stdin, stdout, stderr)
docker cp container:path hostpath - Copy files/folders from container to host
docker cp hostpath container:path - Copy files/folders from host to container
docker export container - Export container contents as a tar archive
docker exec container args - Run command in existing container
- Useful for debugging
docker wait container - Wait until the container terminates
- Returns exit code
docker commit container image - Commit a new docker image
- Asa a snapshot of the container

Image Management

docker images - List all local images
docker history image - Show the image history (list of ancestors or layers)
docker inspect image - Show low-level infos (in JSON format)
docker tag image tag - Tag image with a label tag
docker commit container image - Create an image (from a container)
docker import url [tag] - Create an image (from a tar archive)
docker rmi image - Remove image

Image Transfer

docker pull image[:tag] - Pull image from registry
docker push image[:tag] - Push image to registry
docker search text - Search an image on registry
docker login - Login to registry
docker logout - Logout from registry
docker save repo[:tag] - Export image/repo as tar archive
docker load - Import image from tar archive
docker-ssh image - Script to transfer images via SSH between two daemons

Builder

FROM image|scratch - Base image to build on
MAINTAINER email - Author of the image
COPY path dst - Copy files from host to image
ADD src dst - Same as COPY but un-tar archives and accept HTTP urls
USER name - set the default username
WORKDIR path - set the default working directory
CMD args - set the default command
ENV name value - set an environment variable

Docker-Compose

The docker-compose utility is used to manage multiple containers together. Very often we need to run multiple containers together to make an application work. And they need very specific configurations to work together, especially in terms of file systems and networking.

The docker-compose.yml file is used to configure the containers. As the .yml extension suggests, it is written in YAML format.

All services are defined in the docker-compose.yml file as named dictionaries. Then each keyed service can have many different kinds of docker configurations. image, is the only required configuration and it's the docker image of that service. Other common configuration keys are build, command, environment, ports and more.

Example

version: '3.4'
services:
  expressrestaurantswagger:
    image: jrwtango/expressrestaurantswagger
    build:
      context: .
      dockerfile: ./Dockerfile
    environment:
      NODE_ENV: development
    ports:
      - "3000:3000"

This starts a container from the jrwtango/expressrestaurantswagger image. The build configuration is used to build the image from the Dockerfile in the current directory. To specify environment variables, we use the environment configuration. The NODE_ENV variable is set to development to specify the environment for node. Finally ports is used to map the container's port 3000 to the host's port 3000. When running docker-compose up, the container will be started and the application will be available at http://localhost:3000.