DEVOPS FOR EMBEDDEDSOFTWARE DEVELOPMENTScott HallockMay 20, 2013
Agenda• Introduction• What We Do• How We Do It• Strengths and Challenges
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
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
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
Continuous Integration Review Build Deploy Test Integrate
Continuous Integration Deployment• Datacenter-quality hardware• Rack-mountable form factor• Stable, controlled operating system and management software• Well-defined power and thermal characteristics
Embedded Continuous Integration Review Build Load Test Integrate
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
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
Time Constraints 90 minutes Review Build Load Test Integrate 15 minutes
Preverification 90 minutes, many changes Review Build Load Test Integrate Build 60 minutes, one change
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.
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.
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?
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
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” />
repo: Project Addition Build Test Approve git push!!!
repo: Branch Change Build Test Approve git push!!!
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?
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
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.
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
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/
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
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
Challenge: Build Distribution Build Test Approve git push 25GB x Boulder, ~50/day San Diego, Santa Clara, India, China, Korea…