Docker

Installation

Install docker using your package manager and then start the service.

To play with docker, you will need to run things as root or be part of a group that has access to docker's socket.

See more here: https://docs.docker.com/engine/installation/linux/linux-postinstall/

Usage Reference

Command	Description
docker images	Lists docker images that you created or pulled using docker pull
docker pull	Pulls a docker image from a registry (can be from docker.io or a private registry) Version numbers can be given after a colon.
docker run	Runs a command in a container. Eg. docker run alpine ls -l For commands that require an interactive shell, pass in -it. Pass in --name for a custom name instead of a long hash Pass environment vars using -e Pass -d to detach immediately Pass -P to specify the image
docker ps	Lists containers that are running. Pass -a to see all containers that executed.
docker port	shows the port mapping between the container and the host.
docker stop	Stop a container
docker kill	??
docker rm	Removes a container. Use -rf to stop and remove.

Creating an Image

To create an image:

• Create a directory containing any custom files
• Create a Dockerfile in the directory.
• Run docker build to build the image

Dockerfile

The docker file should a the minimum contain:

# The base image to use
FROM baseimage:version

# What to run when the image is started. This can contain any number of RUN or COPY commands
RUN yum install any-dependencies

# Expose any ports that are required
EXPOSE 80

# run the application
CMD ["python", "/some/app.py"]

Deploying an Application

Use Docker Swarm mode to deploy an application that relies on multiple services where each is a separate docker instance.

The swarm file lets you define each server that is part of the application.

See more at https://github.com/docker/labs/blob/master/beginner/chapters/votingapp.md

Questions

• How are updates to the base image done? Does it automatically update containers relying on it? Or will containers need to be rebuilt again?
• How is data kept persistent? Does it need to be copied out/in everytime it is to be rebuilt?
• NFS access from the container?
• Domain trust - is it the same as a regular VM?

Could it be used for...

• dictd (probably easily)
• WebCat (swarm tomcat + MySQL?)
• ftp (Requires NFS)
• compute balancer
• firewall manager (swarm apache + MySQL)

See Also

• https://github.com/docker/labs/tree/master/beginner/