Quick Docker

(Up-to-date source of this post.)

Docker is a container technology. It's a well timed fusion of

• kernel features
• filesystem tricks
• networking hacks

Think of a container not as a virtual machine but a very lighweight wrapper around a single Unix process.

Docker revision controls

1. filesystem layers
2. image tags

Terminology

Docker server - the docker command run in daemon mode on a Linux host:

$ sudo docker -d -H unix:///var/run/docker.sock -H tcp://0.0.0.0:2375

Docker image - one or more filesystem layers and metadata that represent all the files required to run a Dockerized application

Docker container - a Linux container that has been instantiated from a Docker image

Working with Docker images

To launch a container

• download a public image
• create your own

To create a custom image you need a Dockerfile - each line in a Dockerfile creates a new image layer that is stored by Docker

Build an image:

git clone https://github.com/spkane/docker-node-hello.git
cd docker-node-hello
docker build -t example/docker-node-hello:latest .

Run an image (or a container?):

docker run -d -p 80:8080 example/docker-node-hello:latest

• -p 80:8080 tells Docker to proxy the container's port 80 on the host's port 8080 (port binding)
• example/docker-node-hello:latest is a tag

Remove an image:

docker images
docker rmi <image_id>

Remove all images on your Docker host:

docker rmi $(docker images -q -)

Working with Docker containers

A container is a self-contained execution environment that shares the kernel of the host system and which is (optionally) isolated from other containers in the system.

Containers are a Linux only technology.

Create a container (see also "Run an image" above):

docker run --rm -ti ubuntu /bin/bash 

• run - create + start
• --rm - delete the container when it exits
• -t - allocate a pseudo-TTY
• -i - interactive session, e.i. keep STDIN open
• /bin/bash - executable to run within the container

Get into a running container:

docker ps
docker exec -it <container_id> /bin/bash

Stop a container:

docker stop <container_id>

Remove a container:

docker ps -a
docker rm <container_id>

Remove all containers on your Docker host:

docker rm  $(docker ps -a -q)

Sources

• Docker: Up & Running (2015)
• Unix and Linux System Administration Handbook, 5th ed. (2017)