Short set of slides, brief intro to Git then shared experiences migrating from other SCM tools to Git.

1. Introduction to Git Administration
For New Administrators
Shawn Doyle
ReleaseTEAM Inc
sdoyle@releaseteam.com
www.linkedin.com/in/releaseteam/
http://twitter.com/ReleaseTEAMInc

2. Premium SCM Consulting firm since 1999
Focus on Software Configuration Management
On site and remote consulting services
– Build Automation
– CM tool administration, customization, upgrades, migrations
Classroom training / hands-on mentoring
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ClearCase ClearQuest Jenkins
Git RTC Build Forge
SVN Jira Electric Commander
Shawn Doyle - ReleaseTEAM

4.  For the administrator new to Git
 An overview of Git
 Workflows
 Common admin tasks
 Access control
 Triggers
 Stories from the trenches
Subversion & Git Presentation
Agenda
Slide 4

5. So you now are a Git Admin

6. Git has sprung up in many organizations. Spreading like
a wild fire from the development groups.
– Developers want less restrictions to their productivity
– SCM is always seen as a restriction and rarely a necessary one
SCM admins are finding they need to support Git
regardless of existing corporate standards.
SCM admins need to find a way to control the chaos.
Most commercial SCM tools now support Git as a client.
Don’t panic Git is fun, powerful and it is the future.
Subversion & Git Presentation
Wait.. What? how did this happen
Slide 6

7. DVCS
– Learn the difference
Users
– Training
– Indulging the Git promoter(s)
Many solutions to common problems
– Authentication
– Workflows
– Multiple available UIs
Cleaning up after user mistakes
Subversion & Git Presentation
What am I in for?
Slide 7

8. 1. RTFM http://git-scm.com/book
2. Now that you read the Git book, go thru these tutorials
3. Watch these videos - Google Tech Talks
Linus Torvalds on git
Randal Schwartz on Git
4. RTFW
https://git.wiki.kernel.org/index.php/Main_Page
5. Create a repo and start playing!
Subversion & Git Presentation
How I learned Git
Slide 8

9. Tutorials
http://try.github.io/levels/1/challenges/1 Code School
https://www.atlassian.com/git/tutorial/git-basics Atlassian's Git tutorial
http://gitready.com/ Git Ready
https://www.kernel.org/pub/software/scm/git/docs/everyday.html
Everyday GIT With 20 Commands Or So
Videos - Google Tech Talks
http://www.youtube.com/watch?v=4XpnKHJAok8 Linus Torvalds
http://www.youtube.com/watch?v=8dhZ9BXQgc4 Randal Schwartz
Wiki
https://git.wiki.kernel.org/index.php/GitCommunity|Git Community Wiki
Subversion & Git Presentation
Resources
Slide 9

10. Git Overview
Subversion & Git Presentation Slide 10

11. When coming from another SCM system to Git you need
to shift how you think about how version control works.
In a more classic SCM you think of it as a system that
versions files in a tree or directory structure.
Git is better thought of as a system that versions trees of
files.
Biggest Obstacle

12. Stores whole copies of the repo
– No file deltas
– Entire tree is captured at each commit not just the files that
changed, a snapshot of the repo
Branches and tags
– Are pointers to commits
– Very fast and light weight
Subversion & Git Presentation
How Git Works
Slide 12

13. Git is:
– Powerful
– Complex
– Fast (local)
– worthy contender to replace many commercial tools
– the solution you are looking for
Object Storage
– Blobs
– SHA1s or hashes
– Trees
Perl like syntax
– ^ $ ~ …
Subversion & Git Presentation
Not Scared yet?
Slide 13

14. Workflows

15. Centralized
– Central repository
Feature Branch
– Central repository + branching per features
Gitflow
– Branches per features, releases and bug fixes
Forking
– Distributed workflow
Workflows

16. Uses a central repository
– single point-of-entry for all changes
– Everyone clones from the central repo
– Everyone pull/pushes from the same repo
Benefits
– SCM Admin can put controls/triggers on the central repo
– Security can be setup using tools like
• Stash
• Gitolite
• Gitosis
– SCM Builds and Deploys can be maintained from a clone of the
central repo.
Centralized

17. Development of features in isolated branches
– Allows features to be developed independently
As a feature is finished it is merged to the master branch
Subversion & Git Presentation
Feature Branch
Slide 17

18. Branches are focused around releases
Branches are also used for
– Release
– Integration or Test
– Features
Strict rules on how and when branches interact
Subversion & Git Presentation
Gitflow
Slide 18

19. Repos are forked per developer
– Developers work in isolation
One Repo is declared as the Official Repo
– A Project Maintainer integrates the Repos
– Developers sync with the Official Repo
Subversion & Git Presentation
Forking
Slide 19

20. Common Admin Tasks

21. What to Migrate? Snapshot in time or all history?
– Push for converting a snapshot in time
– If that fails, then try for a few key slices
– Arguments
• Why burden the new repo with all the history
• Populating new workspaces will take longer
• Leave old SCM system in a locked down state for reference
– Refactoring
• Always a good time to refactor when switching SCM system
• Can cause headaches if under deadlines
– Builds
• How dependent were you on the old SCM for builds
– Paths
– Build tools (e.g. clearmake)
– APIs, Libs
Migration Considerations

22. Client and Server concepts
Use a Client side hook for actions
– Commit
– Merge
– Rebase
Server Hooks
– Notification
– Rejecting Pushes
Hooks need to be copied to the repos
– Hooks are not part of cloning
– Hooks do not get updated with pull/pushes
In general, use hooks in Git to encourage workflow or for
notifications. Do not rely on them to enforce security
Subversion & Git Presentation
Hooks
Slide 22

23. Be Clever
– There is no one way to provide Security
– There is no single definition of Security
SSH keys
Git Repository Management
– Stash
– Gitolite
– Github
Triggers
Subversion & Git Presentation
Security
Slide 23

24. Sometimes a user removed something they didn’t mean
to.
The following commands are your friends when trying to
figure out what to restore and from where.
– Git log
– Git relog
– Git reset
– Git update-ref
Repos for backups
– Create clones on a safe network disk
– Pull to them once a day (or once a week)
– Use them to recover files or as a reference
Subversion & Git Presentation
Recovering files
Slide 24

25. Stories from the trenches

26. Builds failed after migrating a project from ClearCase to
Git
– Dev group certain the migration to Git had failed
– Build depended on a large number of sub directories to exist
– Git does not add empty directories
• It needs a blob to point to a directory for the directory to exist.
– Solution was to initially add the missing directories
• Created .temp files in each empty dir
• This creates a blob and the directory is added to Git
– Long term solution
• Encourage them to fix their build Ant/Make files.
Empty Directories

27. A user added multiple large files to his repo
– Then committed them and pushed them to the central repo
User removed them with ‘git rm –rf’
Why is this bad?
– Clone commands went from seconds to 20 minutes
Why?
– Git didn’t remove the large files from the initial commit
– Clone copies the entire repo locally, those files while no longer
visible are still copied
Solution
– Git filter-branch
– Git gc
– Git prune
Subversion & Git Presentation
Slow Clones
Slide 27

28. Client Requirements
– Contractors limited to sub dirs.
– All files in a single Repo.
Git by design
– Does not preserve directory permissions
– Hooks run before or after a Git command
– Submodules don’t offer additional protections
• Also broke the client single repo requirement
Subversion & Git Presentation
Directory Isolation
Slide 28

29. Client workflow depended on Tags
Git Tags are not shared by default
– Tags need to be explicitly;
• Pushed to the remote
• Pulled locally
Solutions
– Reevaluate Workflow
– Share pull command with Tag name
– Share Hash
Subversion & Git Presentation
Universal Tags
Slide 29

30. Client wanted to control who could create a local repo
– Git is not designed to do this
You can limit who can clone from a central Repo
– Stash/Gitolite
– SSH Keys
Once a Repo is cloned
– Nothing is stopping the user from cloning it again
– They can allow others to clone
Solution
– Lock down who can push back to the central Repo
Subversion & Git Presentation
Controlling local repos
Slide 30

31. Client wants to Clone one subdir of a Repo
– Build requires entire Repo
– Deploy requires one sub dir
– Build happens weeks before the deploy
– Deploy wants a fresh Repo
• Just build results and deployment script
Solution
– Submodules
Subversion & Git Presentation
Partial Clone
Slide 31

32. Questions
Shawn Doyle
ReleaseTEAM Inc
sdoyle@releaseteam.com
www.linkedin.com/in/releaseteam/
http://twitter.com/ReleaseTEAMInc