Gerrit Code Review

Main sponsor GerritLuca Milanesio

Agenda • Agile and the broken build dilemma • Can Git solve it ? • “Agile” workflow with Git • Gerrit: the smart way • Just about code-review ? • Let’s play with Gerrit live !review.GerritForge™.com Copyright © 2012 – LMIT Software

Continuous Integration is GOOD • Live “weather forecast” of the project • Detect and resolve conflicts earlier • Bring TDD to life • Enforce collective code ownership • … and much morereview.GerritForge™.com Copyright © 2012 – LMIT Software

Broken build dilemma: how to avoid it ? 1. Do not PUSH until you’re 100% sure of GREEN bar 2. Create multiple personal CI builds and validate builds before PUSH 3. Install a “Jenkins Build Game” plug- in and get free beers  … DO ANY OF THEM REALLY WORK ?review.GerritForge™.com Copyright © 2012 – LMIT Software

Git … can you help out ? Git short story: the anti-Subversion • Apr 2005 – Linus writes PERL scripts for Linux Kernel SCM • Jul 2005 … Git 0.99 is out ! Git principles: • Continuous branching / merging / rebasing / stashing • Distributed repositories • Distributed patch distribution • Early integration (before breaking the CI)review.GerritForge™.com Copyright © 2012 – LMIT Software

Git topic-branches workflow B4 B5 topic1 A1 A2 A3 master C2 C3 C4 topic2 Agile workflow – one topic branch per story • Keep on branch whilst RED / AMBER bar • Continuous rebase on master • Merge on GREEN barreview.GerritForge™.com Copyright © 2012 – LMIT Software

Problem resolved ? • Let’s use Git then ? “My repo is the master” “Git is all about peer-to-peer dev” “Who has reverted my commits ? … !$@#!$!” • Git doesn’t enforce any policy  Peer-to-peer development allowed  Dictatorship or anarchy of changes are both allowed … is there a “better Git” out there ?review.GerritForge™.com Copyright © 2012 – LMIT Software

Gerrit, brief history Google Mondrian The idea: Guido Van Rossum  Code-review for Perforce  Porting to SVN and OpenSourced Rietveld  Python-based 2008 - Project fork for AOSP (Shawn Pearce / Joe Onorato) Gerrit Rietveld  Name changed to Gerrit Rietveld  Based on Git  Set of “patches” on original Guido’s Rietveld project gerrit 2009 - Gerrit 2, the Java + GWT rewriting (Shawn Pearce)review.GerritForge™.com Copyright © 2012 – LMIT Software

What is Gerrit today ? • 100% pure Java SSH and HTTP Git backend  Powered by JGit • GWT Web-view administration  Users and Groups  Project and branch security  Git repository browsing • Git repository replication engine • Code collaboration and review • Code validation through Jenkins Triggersreview.GerritForge™.com Copyright © 2012 – LMIT Software

Gerrit: high level workflow CI Build: OK master A1 Verified: -1 Verified: +1 (build failed) (build OK) C2 C2* refs/for/master clone push push local A1 C2 C2* masterreview.GerritForge™.com Copyright © 2012 – LMIT Software

Gerrit: high level workflow CI Build: OK master A1 Verified: -1 Verified: +1 (build failed) (build OK) C2 C2* refs/for/master Reviewed: +2 clone push push local A1 C2 C2* masterreview.GerritForge™.com Copyright © 2012 – LMIT Software

Gerrit: high level workflow CI Build: OK CI Build: OK master A1 C2* Verified: -1 Verified: +1 (build failed) (build OK) C2 C2* refs/for/master Reviewed: +2 clone push push local A1 C2 C2* masterreview.GerritForge™.com Copyright © 2012 – LMIT Software

Cool, isn’t it ? • Gerrit allow “automatic” topic-branches • Triggers with Jenkins branch validation • Enforce collective code-ownership  People “interacts” with the code changes  Discussion on style and architecture  Democratic voting (+1 / -1) • Project history  Reason behind changes is recorded in code-reviewreview.GerritForge™.com Copyright © 2012 – LMIT Software

1. Set-up • Option-A: download and install 1. Download from http://code.google.com/p/gerrit/downloads/list 2. Gerrit install wizard: java –jar gerrit-2.2.2.1.war init -d ~/gerrit 3. Run Gerrit: ~/gerrit/bin/gerrit.sh start • Option-B: Gerrit as hosted service  Assembla.com (free for OpenSorce projects)  GitEnterprise.com (free up to 10 users)review.GerritForge™.com Copyright © 2012 – LMIT Software

2. Create user and add SSH keys • Option-A: not easy   Gerrit doesn’t support a “local user registry”  Options: LDAP or OpenID • Option-B: use the provider user registration  Assembla: https://www.assembla.com/signup  GitEnterprise: https://gitent-scm.com/signupreview.GerritForge™.com Copyright © 2012 – LMIT Software

4. Create a Gerrit project • Gerrit Project is:  Git repository (use “path notation” to organise projects)  Access permissions  Code-review and change-sets • Option-A: use Gerrit SSH command $ ssh -p 29418 lmilanesio@localhost gerrit create-project lmit/33degree • Option-B: user the provider-specific page  Assembla: N/A (only 1 project associated to your “space”)  GitEnterprise: https://gitent-scm.com/newreporeview.GerritForge™.com Copyright © 2012 – LMIT Software

5. Clone repo from Gerrit • Git SSH repository URL is: ssh://<user>@<host>:29418/<Gerrit project>.git • Gerrit supports HTTP or HTTP/S repository URL: http://<Gerrit URL>/p/<Gerrit project>.git NOTE: For HTTP authentication, put your credentials on ~/.netrc file machine <hostname> login <username> password <password>review.GerritForge™.com Copyright © 2012 – LMIT Software

6. Gerrit Change-Id • SHA-1 GUID of a change-set under review • MUST be last line of commit msg Hint: install Gerrit post-commit hook for auto- generating Change-Id after each Git commit Now all Git commit will auto-generate a Change-Id !review.GerritForge™.com Copyright © 2012 – LMIT Software

7. Submit a change for review • Change for review committed locally • Push to refs/for/<branch> for submitting local Git changes for review on <branch>review.GerritForge™.com Copyright © 2012 – LMIT Software

9. Additional patch-set to Change-Id • Fix the problem locally • Amend the commit (same Change-Id) • Push again to refs/for/<branch> for adding one extra change-setreview.GerritForge™.com Copyright © 2012 – LMIT Software

12. Review merge and submit change • One or more reviewers can “vote” for the change • Authorised users can then “Submit” the change. • Change is automatically merged to masterreview.GerritForge™.com Copyright © 2012 – LMIT Software

… is just about code-review then ? GitHub BitBucket Gitorious Gerrit SSH / HTTPS Free public repo Free private repo Repo security Branch security Code review Hooks / API Replication CI Integration OpenSource / extensible Issue-tracker integrationreview.GerritForge™.com Copyright © 2012 – LMIT Software

Credits and resources • Many thanks to Shawn Pearce, father of Gerrit Its contributors and Google Inc. • Google Gerrit code-review http://code.google.com/p/gerrit/ • Assembla Gerrit http://review.assembla.com • GitEnterprise http://review.gitent-scm.com @gitenterprise Slides available at http://www.slideshare.net/lucamilanesio Follow me: @lucamilanesioreview.GerritForge™.com Copyright © 2012 – LMIT Software

Gerrit: just code-review then ? • Git Security – Groups Define different “roles” in the project System groups • Anonymous users: use for public projects • Registered Users: all users • Administrators: to administer Gerrit • Project Owners: to administer projects • Non-interactive Users: for CI or batch operations Groups can be hierarchical (groups of groups)review.GerritForge™.com Copyright © 2012 – LMIT Software

Putting all together with projects • Git Security: rights to projects Define access rights to Git operations Control the Gerrit identity vs Git author / committer Delegate project administration Assign code-review voting range rights Define who can submit and merge changes Organise project rights hirarchicallyreview.GerritForge™.com Copyright © 2012 – LMIT Software

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Gerrit Code Review

by Luca Milanesio on Mar 20, 2012

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