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

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

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 http://en.wikipedia.org/wiki/Software_configuration_management 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

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) 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

Reasons Not to Use Version Control THIS PAGE INTENTIONALLY LEFT BLANK 9/19/2018 CSCE 606 Configuration Management

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? 9/19/2018 CSCE 606 Configuration Management

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 http://en.wikipedia.org/wiki/Revision_control 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

Centralized vs. Distributed Relatively straightforward workflow Distributed Flexible, supports wide variety of workflows Can get very complex 9/19/2018 CSCE 606 Configuration Management

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

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 9/19/2018 CSCE 606 Configuration Management

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 http://byte.kde.org/~zrusin/git/git-cheat-sheet-medium.png 9/19/2018 CSCE 606 Configuration Management

CSCE 606 Configuration Management Git Cheat Sheet 9/19/2018 CSCE 606 Configuration Management

CSCE 606 Configuration Management Creating Repository > mkdir myproject > cd myproject > git init Initialized empty Git repository in ... /myproject/.git/ 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

CSCE 606 Configuration Management Remotes A repo can keep track of multiple remotes Allows one to share work with multiple collaborators 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

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

Traditional Storage Model 9/19/2018 CSCE 606 Configuration Management

CSCE 606 Configuration Management Git’s Storage Model Dotted boxes were not changed, but are copied, not just delta updates 9/19/2018 CSCE 606 Configuration Management

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: 24b9da6552252987aa493b52f8696cd6d3b00373 Usually a few digits from the beginning suffices to find a commit 9/19/2018 CSCE 606 Configuration Management

CSCE 606 Configuration Management Commit Internally 9/19/2018 CSCE 606 Configuration Management

CSCE 606 Configuration Management Multiple Commits 9/19/2018 CSCE 606 Configuration Management

Multiple Commits and Branch Pointer 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

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

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 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

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

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 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

CSCE 606 Configuration Management Branch Model 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

CSCE 606 Configuration Management Branch Model 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

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) 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management

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 9/19/2018 CSCE 606 Configuration Management