Docker lends itself to a git-style workflow, combining layers of containers in an easy-to-use format, centralized in a universal repository. But what about Docker deployments inside an isolated datacenter? This talk will cover options, pros and cons, and show you a sensible way to develop and distribute Docker containers.

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www.mirantis.com
Docker “Off the Grid”
Matthew Mosesohn
Senior Deployment Engineer

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Agenda
● What are Docker images?
● How to interact with Docker images?
● Where it can go wrong...
● When do you need a base image?
● Building images for production
● Distributing images...
● via tarball
● via Docker Registry

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Docker Images

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What is in a Docker image?
● Base image
● Additional image layers that stack on top of base
● Metadata (links to layers and tags)

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Docker pull
Docker pull steps:
● Fetch metadata
● Fetch layers in parallel
● Load images in order

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Think carefully
● 300mb+ uncompressed
● Depends on external service
● Depends on external build hosts
● Depends on benevolent dictator

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Who is unaffected?
● Public cloud users
● One time deployments with few changes
● Demos/POCs

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Who should be concerned?
● Deployers of custom base images
● Proprietary/unpublished code
● Those concerned about bandwidth
● Those with no direct Internet connection
● Those concerned about consistency 24/7/365
● Those who do CI/CD and need performance

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Where to start?
● Start with a base image
● Take default centos:centos6 or ubuntu image
● Or create your own base
● https://github.com/CentOS/sig-cloud-instance-images
● Keep it simple

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Heavy lifting
● Decide how to transport
● Package and distribute
through APT or Yum
● Distribute tarball via
HTTP/nfs/ftp
● Use Docker Registry
● Build centrally or build on
demand
● Depends on target hosts

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Making the tarball
● Build your images (based on your base image)
● docker save image1 image2 image3 > myimages.tar
● Try lrzip for compression
● Faster than xz
● Better compression than gzip/bzip2
● Try docker-squash to save more time (by Jason Wilder)
● https://github.com/jwilder/docker-squash

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Going the Docker Registry route
● Still uncompressed, but local
● Registry can be deployed as a container!
● docker pull docker/registry
● docker run -d -p5000:5000 -v /data/registry:/tmp/registry
docker/registry
● docker tag myimage localhost:5000/myimage
● docker push localhost:5000/myimage

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Pros and Cons of Docker Registry
● Pros:
● Centralized store of Docker images
● Lightweight app you can deploy anywhere
● Native to Docker
● Cons:
● Not highly available for local data stores
■ But with Amazon S3 or Glance it is decent
● Registry image is large

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Thank you
for your time