Sick of getting paged at 2am and wondering "where did all my disk space go?" This has actually happened to me, and you can learn from my mistakes! New Docker users often start with a stock image in order to get up and running quickly, but that isn't always the right answer. Creating efficient images is often overlooked, but important. Beyond saving resources, using minimal images also delivers important security benefits: include only what you need and not a whole runtime that might have security vulnerabilities. In this session, I'll talk about how to create effective images and lessons I've learned from running containers in production at a number of startups. I'll also cover topics like "how do layers work?" and some things you should think about when creating your images, such as; choosing or creating the right base image; the importance of caching; using RUN statements conservatively; cleaning up as you go. I'll also address best practices; both at a high level with multi-stage builds; and some language-specific best practices, for example, tips and tricks for creating containers for Node.js vs Go. To illustrate these points, we'll cover: * How layers work? * Choosing a base image vs. creating your own * The basics of building minimal images and the importance of choosing a base image vs. creating your own * The basics of building minimal images and the importance of caching * High level best practices for Linux containers (in general, and some language specific examples) * High level best practices for Windows container images * New and improved: multi-stage builds * Good vs. not so good Dockerfile examples * Docker Image Scanning, and other friends * What's up next? Looking to the future for more optimization.

1. Creating Effective Images
Sr Technical Evangelist, AWS
@abbyfuller
Abby Fuller

2. • How do layers work?
• The basics for building minimal images
• High level best practices for Windows containers
• Dockerfiles: the good, the bad, and the bloated
• Let’s get (language) specific
• Tools are here to help
• Looking forward to the future
Agenda

3. How do layers work?

4. What are container layers?
read-only container layers
Thin read-write layer

5. Why do I care how many layers I have?
More layers mean a larger image. The larger the image, the longer
that it takes to both build, and push and pull from a registry.
Smaller images mean faster builds and deploys. This also means a
smaller attack surface.

6. OK, so how can I reduce my layers?
Sharing is caring.
• Use shared base images where
possible
• Limit the data written to the
container layer
• Chain RUN statements
• Prevent cache misses at build for as
long as possible

7. Building minimal images: the basics

8. A Dockerfile is a series of
instructions for building images.

9. Cache rules everything around me
CACHE

10. Let’s start with a Dockerfile
FROM ubuntu:latest
LABEL maintainer abbyfull@amazon.com
RUN apt-get update -y && apt-get install -y python-pip
python-dev build-essential
COPY . /app
WORKDIR /app
RUN pip install –r requirements.txt
EXPOSE 5000
ENTRYPOINT ["python"]
CMD ["application.py"]

11. First step: choosing the right base
From the stock ubuntu image:
ubuntu latest 2b1dc137b502
52 seconds ago 458 MB
From python:2.7-alpine:
alpine latest d3145c9ba1fa
2 minutes ago 86.8 MB

12. Slightly better- choose a different distro
alpine latest d3145c9ba1fa 3.9 MB
python 3.6.1-slim 60952d8b5aeb 200 MB
debian latest 8cedef9d7368 123 MB
python 2.7-alpine b63d02d8829b 71.5 MB
ubuntu latest 0ef2e08ed3fa 130 MB
fedora latest 4daa661b467f 231 MB

13. When do I want a full base OS?
(I do actually like Ubuntu!)
• Security
• Compliance
• Ease of development

14. Let’s look at our original Ubuntu image
FROM ubuntu:latest
RUN apt-get update -y && apt-get install -y python-pip
python-dev build-essential
LABEL maintainer abbyfull@amazon.com
COPY . /app
WORKDIR /app
RUN pip install –r requirements.txt
EXPOSE 5000
ENTRYPOINT ["python"]
CMD ["application.py"]

15. Simple changes, big results
FROM python:2.7-alpine
LABEL maintainer abbyfull@amazon.com
COPY . /app
WORKDIR /app
RUN pip install –r requirements.txt
EXPOSE 5000
ENTRYPOINT ["python"]
CMD ["application.py"]

16. Fewer cache invalidations=smaller images
FROM python:2.7-alpine
LABEL maintainer abbyfull@amazon.com
COPY requirements.txt /app
RUN pip install –r /app/requirements.txt
COPY . /app
WORKDIR /app
EXPOSE 5000
ENTRYPOINT ["python"]
CMD ["application.py"]

17. Got application code?
FROM python:2.7-alpine
LABEL maintainer abbyfull@amazon.com
ONBUILD ADD requirements.txt /app
ONBUILD RUN pip install –r /app/requirements.txt
ONBUILD COPY . /app
WORKDIR /app
EXPOSE 5000
ENTRYPOINT ["python"]
CMD ["application.py"]

18. Let’s recap.
TL;DR: layers represent filesystem differences.
Layers add up quickly with big consequences.

19. Some high-level best practices: Windows

20. Port over existing VM workloads
Convert an existing Windows image:
ConvertTo-Dockerfile -ImagePath c:dockermyimage.wim
Convert from VHD:
ConvertTo-Dockerfile -ImagePath c:vmstest.vhd -Artifact IIS -
ArtifactParam windows-container -OutputPath c:windows-container
cd c:windows-container
docker build -t windows-container .
docker run -d -p 80:80 windows-container

21. Some things to think about
Watch what you build:
c: c: / /windows c:/windows
Building any of those PATHs will make your image very large!

22. Avoid installing packages with MSI
MSI installations are not space efficient. This is not
the same as Linux distros, where you can add, use,
and remove the installation files!
$ Windows/Installer/<package>.msi
Windows saves these files for uninstalls :(

23. Coming up soon
Run Linux containers “as-is” on
Windows Server!

24. Here’s whats really cool though
Build and run everything the same, regardless of
container OS, host OS, or tools. Just docker build
and docker run.

25. …but I’m not a Windows expert
So go to see Elton
instead! He’ll talk on
modernizing .NET apps at
17:10 for the Using Docker
track. He literally wrote
the book.

26. Dockerfiles: the good, the bad, and the
bloated

27. Let’s start out big
FROM ubuntu:latest
LABEL maintainer abbyfull@amazon.com
RUN apt-get update -y
RUN apt-get install -y python-pip python-dev build-
essential
COPY . /app
WORKDIR /app
RUN pip install -r requirements.txt
EXPOSE 5000
ENTRYPOINT ["python"]
CMD ["application.py"]

28. A little bit better
FROM ubuntu:latest
LABEL maintainer abbyfull@amazon.com
RUN apt-get update -y && apt-get install -y python-
pip python-dev build-essential –no-install-recommends
COPY . /app
WORKDIR /app
RUN pip install -r requirements.txt
EXPOSE 5000
ENTRYPOINT ["python"]
CMD ["application.py"]

29. Let’s try a different base
FROM python:2.7-alpine
LABEL maintainer abbyfull@amazon.com
COPY . /app
WORKDIR /app
RUN pip install -r requirements.txt
EXPOSE 5000
ENTRYPOINT ["python"]
CMD ["application.py"]

30. Or, let’s try a custom base container
FROM 621169296726.dkr.ecr.us-
east-1.amazonaws.com/dockercon-base:latest
LABEL maintainer abbyfull@amazon.com
COPY . /app
WORKDIR /app
EXPOSE 5000
ENTRYPOINT ["python"]
CMD ["application.py"]

31. Use RUN statements effectively
RUN apt-get update && apt-get install -y
aufs-tools
automake
build-essential
ruby1.9.1
ruby1.9.1-dev
s3cmd=1.1.*
&& rm -rf /var/lib/apt/lists/*

32. Switching USER adds layers
RUN groupadd –r dockercon && useradd –r –g
dockercon dockercon
USER dockercon
RUN apt-get update && apt-get install -y
aufs-tools
automake
build-essential
USER root
COPY . /app

33. Avoid ADDing large files
BAD:
ADD http://cruft.com/bigthing.tar.xz /app/cruft/
RUN tar -xvf /app/cruft/bigthing.tar.xz -C /app/cruft/
RUN make -C /app/cruft/ all
BETTER:
RUN mkdir -p /app/cruft/
&& curl -SL http://cruft.com/bigthing.tar.xz | tar -xJC /
app/cruft/ && make -C /app/cruft/ all

34. BEST
RUN mkdir -p /app/cruft/
&& curl -SL http://cruft.com/
bigthing.tar.xz | tar -xvf /app/
cruft/
&& make -C /app/cruft/ all &&
rm /app/cruft/bigthing.tar.xz

35. Let’s get (language) specific

36. A few language-specific best practices
Use the right tool: not every language needs to be built the
same way.
•Where possible, use two images: one to build an artifact,
and one from base
•Official language images can be huge: more space
effective to use a more minimal image, but there are
tradeoffs

37. First stop: Golang
Compile, then COPY binary:
$ go build -o dockercon .
$ docker build -t dockercon .
Dockerfile:
FROM scratch
COPY ./dockercon /dockercon
ENTRYPOINT ["/dockercon"]

38. Quick detour: what’s scratch?
Special, empty Dockerfile.
Use this to build your own base images.
Or, use to build minimal images that run a binary and nothing else:
FROM scratch
COPY hello /
CMD [ “/hello” ]
Want more on scratch? Start here.

39. Back to business: Ruby
Official images for Ruby are extra huge. A new base + a little extra
work pays off.
FROM alpine:3.2
LABEL maintainer abbyfull@amazon.com
RUN apk update && apk upgrade && apk add
curl
bashruby
ruby-dev
ruby-bundler
RUN rm -rf /var/cache/apk/*

40. Next: node.js
If you love yourself, .dockerignore npm-debug.log.
Seriously.
But most importantly, cache node_modules:
COPY package.json .
RUN npm install --production
COPY . .
This way, only run npm install if package.json changes.

41. Java!
Multi-stage builds are your friend:
FROM maven:3.5-jdk-8 as BUILD
COPY --from=BUILD
Like, Golang, this let’s you build an artifact in one stage, and simply
run the binary in the second stage, resulting in more minimal final
images.
More on multistage builds up next.

42. Multi-stage builds
FROM ubuntu AS build-env
RUN apt-get install make
ADD . /src
RUN cd /src && make
And for the second Dockerfile, copy from #1:
FROM busybox
COPY --from=build-env /src/build/app /usr/local/bin/app
EXPOSE 80
ENTRYPOINT /usr/local/bin/app

43. Tools are here to help

44. With great containers comes great responsibility
• Document!
• Automate where possible
• AWS has a few tenants for
services: secure, resilient,
scaleable
• Lean on (the right) tools for a
helping hand

45. Docker Security Scan

46. Docker Security Scan

47. Docker Image + System Prune
Docker image prune:
$ docker image prune –a
Alternatively, go even further with Docker system prune:
$ docker system prune -a

48. The importance of garbage collection
• Clean up after your containers! Beyond
image and system prune:
• Make sure your orchestration platform
(like ECS or K8s) is garbage collecting:
• ECS
• Kubernetes
• 3rd party tools like spotify-gc

49. Looking forward to the future

50. But wait, there’s always more!
• Always new and better things coming
• Linux and Windows Server
• Official image are multi-platform
• Always new and better minimal
images and operating systems
coming out for containers

51. So what did we learn?
One takeaway: less layers is more.
•Share layers where possible
•Choose or build your base wisely
•Not all languages should build the same
•Keep it simple, avoid extras
•Tools are here to help

52. Useful links
Docker image documentation
Docker scratch
atsea sample app
Arun Gupta on smaller Java images
Elton Stoneman Windows Dockerfiles
Alpine (the base image from the examples)
Running Linux containers on Windows
Docker garbage collection
Image cleanup in Amazon ECS
Image cleanup in Kubernetes
spotify-gc

53. Thanks!
@abbyfuller