The document provides an overview of Docker images, including their structure, how to interact with them, and considerations for using custom base images. It outlines the process of building, distributing, and storing images via tarballs or Docker registries while highlighting who should be concerned about bandwidth and consistency. Additionally, it discusses the pros and cons of utilizing a Docker registry for centralized image storage.

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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● Proprietary/unpublished code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