1. CSCE 606: Configuration Management
Some material from J. Freeman, TAMU

2. CSCE 606 Configuration Management
Outline
Software Configuration Management
Git Basics
Branching
Working with Remotes
Branch Models
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CSCE 606 Configuration Management

3. Software Configuration Management (SCM)
Software configuration management goals:
Configuration identification - identify configurations, configuration items and baselines
Configuration control - implement controlled change process; e.g. change control board to approve/reject change requests against a baseline
Configuration status accounting – record/report all necessary information on status of development process
Configuration auditing – ensure configurations contain all intended parts and are sound w.r.t. specifying documents, including requirements, architectural specs and user manuals
Build management – manage process and tools used for system builds
Process management - ensure adherence to development process
Environment management – manage HW/SW that hosts the system
Teamwork – facilitate team interactions related to the process
Defect tracking – make sure every defect has traceability back to the source
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CSCE 606 Configuration Management

4. CSCE 606 Configuration Management
Version Control
Aspect of software configuration management
Management of changes to documents, source code, web sites,…
Also known as revision control, source code control
Track/control changes over time
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CSCE 606 Configuration Management

5. Version Control System
A tool for maintaining a record of changes in a set of documents
Common tools
CVS, Subversion, Git, Darcs, Mercurial
Also in SCM product, e.g. IBM/Rational ClearCase, Visual Studio ALM
A record of change
E.g. a patch generated with a diff type tool
Set of documents
Source code
Documentation, scripts, Makefiles,…
Works best for text files (contrast to binary files)
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CSCE 606 Configuration Management

6. Reasons to Use Version Control
Helps in collaboration/coordination
Avoid conflicting changes in code/documents
Allows rolling back mistakes
In modules and system
Can maintain different configurations
E.g. different platforms
Avoid divergent code bases
Each providing different features
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CSCE 606 Configuration Management

7. Reasons Not to Use Version Control
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CSCE 606 Configuration Management

8. Reason to Use Version Control For Everything You Do
You find a set of files like this in a directory:
Report_draft.txt
Report.doc
Report2.doc
Report2a.doc
Report_2011_03_02.doc
...
NewReport_2011_05.doc
NewReport_submitted.doc
NewReport_submittedv2.doc
Can I just use the newest?
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CSCE 606 Configuration Management

9. CSCE 606 Configuration Management
Terminology
Repository
Database with complete revision history of all files under version control
Maybe stored as files, relational database,…
Stored as full files and patches to them
Workspace or working tree
Files you are working on, that are tracked by version control system
A checkout of the repository, plus your local changes not committed
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CSCE 606 Configuration Management

10. Centralized vs. Distributed Version Control Systems
Centralized version control systems
One central shared repository
Working tree does not contain history
Subversion, CVS, Perforce
Distributed version control systems
With every working tree, entire repository stored as well
Local changes first committed to local repository, then repositories synchronized
One repository can be dedicated to be the central one, if desired
Git, Darcs, Mercurial
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CSCE 606 Configuration Management

11. Centralized vs. Distributed
Relatively straightforward workflow
Distributed
Flexible, supports wide variety of workflows
Can get very complex
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CSCE 606 Configuration Management

12. CSCE 606 Configuration Management
Outline
Software Configuration Management
Git Basics
Branching
Working with Remotes
Branch Models
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CSCE 606 Configuration Management

13. CSCE 606 Configuration Management
Git
Widely used distributed version control system
Started as system to support Linux kernel development
Pragmatic philosophy
Many tools
Many ways to accomplish tasks and arrange work
Many ways to share repositories/patches
Each VC system has its own terminology, but similar basic concepts
Our discussion will use established Git terms
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CSCE 606 Configuration Management

14. CSCE 606 Configuration Management
Git References
Quick to learn the basic commands
Commands not used every day, hard to remember, but many places to refresh memory:
The Git Community Book
Pro Git book
Git Cheat Sheet
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CSCE 606 Configuration Management

15. CSCE 606 Configuration Management
Git Cheat Sheet
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CSCE 606 Configuration Management

16. CSCE 606 Configuration Management
Creating Repository
> mkdir myproject
> cd myproject
> git init
Initialized empty Git repository in ... /myproject/.git/
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CSCE 606 Configuration Management

17. CSCE 606 Configuration Management
Clone
As an alternative to an empty repository, one can clone an existing repository (repo)
Cloning allows us to create a copy of another repo
Other repos are called remotes
Our clone is called the local repo
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18. CSCE 606 Configuration Management
Remotes
A repo can keep track of multiple remotes
Allows one to share work with multiple collaborators
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19. CSCE 606 Configuration Management
Index
Git provides a special feature called the index
Allows us to compile our commit in pieces, slowly and selectively adding the changes we wish to record
Without the index, we have to specify our changeset in one command
Changes can be removed from the index without affecting the repo
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CSCE 606 Configuration Management

20. CSCE 606 Configuration Management
Outline
Software Configuration Management
Git Basics
Branching
Working with Remotes
Branch Models
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CSCE 606 Configuration Management

21. Traditional Storage Model
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22. CSCE 606 Configuration Management
Git’s Storage Model
Dotted boxes were not changed, but are copied, not just delta updates
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CSCE 606 Configuration Management

23. CSCE 606 Configuration Management
Commit
Whenever we have changes we want to record, we commit them
If we have many changes, we can commit them all at once, or separately according to some criteria
A checksum is computed for every commit, and then the commit is identified, both internally and sometimes also by the programmer, with this checksum
Example:
24b9da aa493b52f8696cd6d3b00373
Usually a few digits from the beginning suffices to find a commit
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CSCE 606 Configuration Management

24. CSCE 606 Configuration Management
Commit Internally
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25. CSCE 606 Configuration Management
Multiple Commits
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26. Multiple Commits and Branch Pointer
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27. CSCE 606 Configuration Management
Branch
Repos will be comprised of branches
A branch is typically created to hold all of the development work for a single issue, like a new feature or the next release
A branch “branches” off another line of development, hence the name
All of its history is copied over to the new branch, but none of the work on the new branch affects the old one
A history is a single time-line of changes
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CSCE 606 Configuration Management

28. CSCE 606 Configuration Management
Outline
Software Configuration Management
Git Basics
Branching
Working with Remotes
Branch Models
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CSCE 606 Configuration Management

29. CSCE 606 Configuration Management
Sharing
When we have some changes committed, we may choose to share them
Remember that agile methods share everything
There are two main ways to share: giving and taking
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CSCE 606 Configuration Management

30. CSCE 606 Configuration Management
Fetch
Every repo keeps a copy of its remote repos
Allows us to interact with remotes without continuous network traffic
Before we can share with one of our remotes, we need to make sure that our copy of it is up- to-date by fetching the latest version
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CSCE 606 Configuration Management

31. CSCE 606 Configuration Management
Merge
To take changes from a remote, we can merge one of its branches into ours
Merging will try to incorporate all of the changes together
Sometimes conflicts will appear
They must be resolved manually before committing
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32. CSCE 606 Configuration Management
Pull
Git provides a short-hand for fetching and merging called pulling
This is the name for taking changes that is common among version control systems
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33. CSCE 606 Configuration Management
Giving
If we want to give our changes to others, one option is to just make them available for pulling
The alternative is to forcefully merge our changes into their repo
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34. CSCE 606 Configuration Management
Push
When we commit our changes into a remote repo, it is called pushing
Commonly limited to a few authenticated contributors to avoid undesirable commits
Requires a pull of the remote to resolve conflicts beforehand
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CSCE 606 Configuration Management

35. CSCE 606 Configuration Management
Merge (continued)
We can merge changes between any two (or more) branches
Not limited to one remote and one local branch
Merging does not change the fact that a branch has a single line of history
The merged branch’s history is either copied (e.g. it becomes part of the code’s family tree) or forgotten
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CSCE 606 Configuration Management

36. CSCE 606 Configuration Management
Outline
Software Configuration Management
Git Basics
Branching
Working with Remotes
Branch Models
9/19/2018
CSCE 606 Configuration Management

37. CSCE 606 Configuration Management
Why Separate Branches?
Separation of concerns
Less contention over the repository
Groups commit according to common theme, allowing easier porting or roll-back
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CSCE 606 Configuration Management

38. CSCE 606 Configuration Management
Possible Branches
Examples
Released versions
Soon-to-be-released versions
Ongoing development
Ideas may never show up in a release, but you never know, so don’t flush the code
Features or topics
Hotfixes
Branch models are generally portable among version control systems
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CSCE 606 Configuration Management

39. CSCE 606 Configuration Management
Branch Model
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40. CSCE 606 Configuration Management
Main Branches
“master”
Each commit is tagged with a version number
Released versions of the product are built from this branch
“develop”
Latest set of features that will go into the next release
Always left in a functioning state (no work in progress)
These branches live forever
Other supporting branches have limited lifetimes
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CSCE 606 Configuration Management

41. CSCE 606 Configuration Management
Release Branches
“release-*”
Whenever the “develop“ branch is feature-complete for the next release, create a release branch off of “develop“
Only bugfixes or new metadata (like version numbers) may be committed
This branch may periodically be merged into “develop“ to pass on the bugfixes
When the release is complete:
Merge it into “master“ and tag
Merge it into “develop“ one last time
Delete it
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CSCE 606 Configuration Management

42. CSCE 606 Configuration Management
Feature Branches
“*” (any unique name)
Whenever a developer wants to begin work on a new feature, bugfix, refactoring,… create a feature branch off of “develop“
Try to break commits into their smallest, independent units
When the feature is complete and will be included in the next release:
Merge it into “develop“
Delete it
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CSCE 606 Configuration Management

43. CSCE 606 Configuration Management
Hotfix Branches
“hotfix-*”
Sometimes we make mistakes
Whenever we need an urgent fix for a released version, create a hotfix branch off of “master“
Treat it exactly like an unplanned release branch
When a hotfix is complete:
Merge it into “master“ and tag
Merge it into “develop“
Delete it
This model only supports hotfixes for the latest release
If you want to support old versions after new ones have been released, then do not delete release branches
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CSCE 606 Configuration Management

44. CSCE 606 Configuration Management
Branch Model
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CSCE 606 Configuration Management

45. CSCE 606 Configuration Management
Developer Model
Different teams require different contributor / maintainer structures
Factors:
Number of contributors
Affiliations
Centralized workflow sufficient for small teams
Distributed version control can still be used to provide centralized workflow
The shared repo has special status, but no special technical features
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CSCE 606 Configuration Management

46. CSCE 606 Configuration Management
Large Team
Distributed workflow is better for large teams
Single blessed repo for main branches
Developers
Pull from blessed repo
Push supporting branches to their own repos
Integration manager
Pulls supporting branches from developers
Merges into main branches
Pushes to blessed repo
Public and private repos for developers can be the same
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CSCE 606 Configuration Management

47. CSCE 606 Configuration Management
Huge Team
Single integration manager can become overloaded as the team grows
Solution: introduce hierarchy
Feature managers (lieutenants)
Product manager (dictator)
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CSCE 606 Configuration Management

48. CSCE 606 Configuration Management
Developer Model
These models demonstrate the benefits of a distributed version control system
Easy transition between the workflows as the team grows
Subgroups can be formed by simply dedicating a single developer’s repo as a blessed subgroup repo, and others adding that as a remote
Central server grows more slowly than the amount of work
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CSCE 606 Configuration Management

49. Configuration Management Summary
Typical code development has graph-like dependencies
Use version control systems to manage code
Permits synchronization and consistency across developers
Permits roll back to previous point in code history
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CSCE 606 Configuration Management