Introduction to git administration

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

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

 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

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.
Wait.. What? how did this happen
Slide 6

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
What am I in for?
Slide 7

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!
How I learned Git
Slide 8

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
Resources
Slide 9

Git Overview
Subversion & Git Presentation Slide 10

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

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
How Git Works
Slide 12

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
– ^ $ ~ …
Not Scared yet?
Slide 13

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

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

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

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

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
Forking
Slide 19

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

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
Hooks
Slide 22

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
Security
Slide 23

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
Recovering files
Slide 24

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

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
Slow Clones
Slide 27

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
Directory Isolation
Slide 28

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
Universal Tags
Slide 29

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
Controlling local repos
Slide 30

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
Partial Clone
Slide 31

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

Introduction to git administration

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