Docker.md

Notes on Docker.

Starting a Docker machine

docker-machine start :name: && eval "$(docker-machine env :name:)"

Where :name: is the name of the machine you want to start, e.g. to start default:

docker-machine start default && eval "$(docker-machine env default)"

Containers

docker run runs containers.

E.g.

docker run ubuntu:14.04 /bin/echo 'Hello world'

Interactive Run

docker run -t -i ubuntu:14.04 /bin/bash

• -t: assigns a pseudo-tty or terminal inside our new container
• -i: allows us to make an interactive connection by grabbing the standard in (STDIN) of the container

You can also express this as:

docker run -it ubuntu:14.04 /bin/bash

Daemonized Run

docker run -d ubuntu:14.04 /bin/sh -c "while true; do echo hello world; sleep 1; done"

This time we get a container ID. Inspect the container ID with docker ps, then inspect the container logs with docker logs :name:, where :name: is the name assigned by Docker, as shown in docker ps. Stop the container with docker stop :name:.

Next.

Running a web app

docker run -d -p 80:5000 training/webapp python app.py

Where:

• -d: runs container in background and prints container ID
• -p 80:5000: maps port 5000 inside the container to port 80 on the local Docker host

NOTE: To access the running web app, get the IP address of the local Docker host (via docker-machine ip :name:). E.g., if this is 192.168.99.100, then the web app will be available at http://192.168.99.100:80/.

Next.

Stopping that web app

Find the container name, via docker ps, then:

docker stop :container_name:

Where :container_name: is the name of the container, obvs. E.g.

docker stop stoic_albattani

NOTE: We can also start it again! docker start :container_name:. Restarts too! docker restart :container_name:. And even remove it! docker rm :container_name:.

Next.

Images

Via.

Listing images

docker images

Produces something like:

REPOSITORY          TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
mongo               latest              9108562f532a        5 days ago          261.3 MB
ubuntu              14.04               91e54dfb1179        6 weeks ago         188.4 MB
ubuntu              latest              91e54dfb1179        6 weeks ago         188.4 MB
hello-world         latest              af340544ed62        8 weeks ago         960 B
training/webapp     latest              02a8815912ca        4 months ago        348.8 MB

When we run a container, we refer to a tagged image, i.e. docker run -t -i ubuntu:12.04 /bin/bash will run an Ubuntu 12.04 image.

Preloading images

Use docker pull, e.g.:

docker pull centos

Searching for images

On the Docker Hub, via docker search, e.g.

docker search nodeschool

Rolling our own

2 ways to do this:

1. Update an image
2. Describe an image using a Dockerfile

The latter is easier when sharing an image with a team, easier to collaborate, track changes.

Example Dockerfile:

# This is a comment
FROM ubuntu:14.04
MAINTAINER Kate Smith <ksmith@example.com>
RUN apt-get update && apt-get install -y ruby ruby-dev
RUN gem install sinatra

Dockerfile reference.

Build an image from a custom Dockerfile using docker build, e.g. assuming Dockerfile is in the cwd:

docker build -t ouruser/example:v2 .

Then create a container for the new image:

docker run -t -i ouruser/example:v2 /bin/bash

NOTE: You can also tag an image (docker tag), push an image to Docker Hub (docker push), remove an image from the host (docker rmi).

Next.