A brief overview of DevOps practices and tools. Presented at the DevOps Boulder Meetup, May 20th, 2013.

1. DEVOPS FOR EMBEDDED
SOFTWARE DEVELOPMENT
Scott Hallock
May 20, 2013

2. Agenda
• Introduction
• What We Do
• How We Do It
• Strengths and Challenges

3. Introduction
BAIT
• Build, Automation, Integration, and Test
• Continuous integration and automated release for Linux
software products
• 3-5 Linux-based operating systems
• Software releases nearly every day
• Build Linux from source thousands of times per day
• Support a worldwide Linux developer community of more than
1,000
• More than 50 actively developed codelines
• Integrate more than 200 code changes per day

4. Objectives
• High-level overview of embedded DevOps processes and
practices
• Start an exchange of knowledge between embedded and
non-embedded DevOps communities
• Interactivity
• Please interrupt to ask questions
• Detailed, tangential discussions are welcome

5. Embedded Development Is Different
• Tools don’t evolve quickly
• Command line compilers
• Everybody loves the preprocessor
• printf debugging
• Eclipse viewed with suspicion
• Product focus
• Customers get the code, not just the experience
• Fix it, ship it, forget it
• Standard release: zip archive
• Many similar codelines under active development simultaneously

6. Continuous Integration
Review Build Deploy Test Integrate

7. Continuous Integration Deployment
• Datacenter-quality hardware
• Rack-mountable form factor
• Stable, controlled operating system and management
software
• Well-defined power and thermal characteristics

8. Embedded Continuous Integration
Review Build Load Test Integrate

9. Target Load Challenges
• Developer-quality hardware
• Irregular form factor
• Unstable loading software, boot code, operating system
• Unknown power and thermal characteristics
• Slow and unstable JTAG, USB loading interfaces

10. Target Load Solutions
• Single controlling server for each target hardware board
• Physical access to production hardware
• Easily reconfigure physical racks to accommodate novel form
factors
• Repair or replace unstable, malfunctioning target hardware
• Fault-tolerant software
• Lots of retries!
• Heuristics to infer target state based on observable outputs
• Change the target hardware design

11. Time Constraints
90 minutes
Review Build Load Test Integrate
15 minutes

12. Preverification
90 minutes, many changes
Review
Build Load Test Integrate
Build
60
minutes,
one
change

13. Automated Release
Build Test Approve git push

14. Code Change Control: git
• http://git-scm.com
• Distributed is great!
• Developers can work offline, at customer sites with no network
access.
• Collaboration is easier. Everyone has complete history.

15. git Problems
• Everyone gets everything
• Do you check in a helper binary every time you change it?
• Did you accidentally commit some trade secrets and then revert
them later?
• Did your developers include an estimate of your customers’
intelligence in their commit message?
• You create integration tags fifty times per day.
• Your continuous integration system creates “temporary” integration
branches twenty-five times per day.

16. git Problems
• git trees become unusable over time. Are you garbage
collecting?
• On your central repositories?
• When you mirror your central repositories?
• On your external release servers?
• On your Continuous Integration build machines?

17. git Problems
• Cherry-picking
• I can just have the two changes I want for today’s release? Great!
• Breaks all traceability, barring commit message kludges

18. Codeline Definition: repo
• http://source.android.com/source/using-repo.html
• Allows for many git projects to be combined into a single
source tree and operated upon as a single entity.
• Developers use it to download and sync code, most use
git commands for everything else.
<project name=“kernel/msm” path=“kernel”
revision=“refs/heads/msm-3.4” />
<project name=“kernel/lk”
path=“bootable/bootloader/lk”
revision=“refs/heads/master” />

19. repo: Project Addition
Build Test Approve git push!!!

20. repo: Branch Change
<project name=“kernel/msm” path=“kernel”
revision=“refs/heads/msm-3.4” />
<project name=“kernel/lk”
path=“bootable/bootloader/lk”
revision=“refs/heads/master” />
<project name=“kernel/msm” path=“kernel”
revision=“refs/heads/msm-3.4” />
<project name=“kernel/lk”
path=“bootable/bootloader/lk”
revision=“refs/heads/stable” />

21. repo: Branch Change
Build Test Approve git push!!!

22. repo: Branch Change
• Merge?
• “master” branch contains dozens of bugs. You just merged them
with your stable branch.
• Force push?
• Now your customer doesn’t understand what happened to all the
changes they painstakingly integrated for the last month.
• Create new branch on release server?
• Customer still has to re-integrate their changes.
• At least the old branch is available for reference.
• Stop doing that!
• How am I supposed to make my release?

23. repo: Shared Branches
customer-1.xml:
<project name=“kernel/msm” path=“kernel”
revision=“refs/heads/msm-3.4” />
<project name=“kernel/lk”
path=“bootable/bootloader/lk”
revision=“refs/heads/customer-1” />
customer-2.xml
<project name=“kernel/msm” path=“kernel”
revision=“refs/heads/msm-3.4” />
<project name=“kernel/lk”
path=“bootable/bootloader/lk”
revision=“refs/heads/customer-2” />

24. Gerrit: Code Review and More
• https://code.google.com/p/gerrit/
• Code review, access control, source code mirroring

25. Gerrit: Code Review
• States Tracked:
• Code Review (-2 - +2): Peer opinion of design and code quality
• Verified (-1 - +1): Code works at runtime
• Roles
• Author/Committer
• Approver
• Integrator

26. Gerrit: Access Control
• Most actions in Gerrit are access controlled
• Code visibility
• Upload
• Review
• Merge
• Access control can be based on users, on local groups, or
on LDAP groups.
• Access control is complex. Automation is recommended.

27. Gerrit: Mirroring
Master
Slave Slave Slave
• Single master
• Slaves can’t mirror to other slaves
• Smart git push based mirroring
• Better than any mirroring scheme not based on application layer
knowledge of git
• Errors not handled gracefully
• Obvious errors are re-queued for later retries

28. Code Aurora Forum
• http://codeaurora.org

29. Other Tools
• Electric Commander
• http://www.electriccloud.com/products/electriccommander.php
• Jira
• https://www.atlassian.com/software/jira/overview
• BlackDuck
• http://www.blackducksoftware.com/products/black-duck-suite
• Gitolite
• http://gitolite.com/gitolite/

30. Strengths
• Chasing the sun
• Operational teams in major timezones
• Handoff procedure is well understood
• Cheap scaling
• Use simple, dumb tools and relentlessly parallelize
• Understand where human intervention is inevitable
• Sync, build efficiency
• Custom software atop repo for very efficient repo syncs
• Fastest clean builds in the business
• Automated release
• Very complex branching structure is released automatically multiple
times per day

31. Challenge: Source Code Distribution
Master
Slave Slave!!! Slave
• Single master mirroring has scaling limits
• Git push is CPU intensive
• Gerrit doesn’t report well when a slave is out of sync
• Custom software needed
• An independent and easily monitored sync solution is
desired

32. Challenge: Build Distribution
Build Test Approve git push
25GB x Boulder,
~50/day San
Diego,
Santa
Clara,
India,
China,
Korea…

33. Challenge: Two-Way Integration
Internal Codeline
Integrated Codeline
Partner Codeline