Configuration. Monday, November 30, :28 AM. Configuration

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1 Configuration 11:28 AM Configuration refers to the overall set of elements that comprise a software product ("configuration items") software components modules internal logical files test stubs and scaffoldings external documentation user manual FAQs getting started guides tutorials internal documentation requirements design test plan More generally, includes environmental conditions necessary for product function (e.g., external libraries, files, etc) environmental conditions required to develop the software (e.g., software tools) These are lists of conditions. Three concepts of configuration Configuration of the files. Configuration of the development environment. Configuration of the deployment environment. Configuration Page 1

2 Configuration Page 2 Change 11:32 AM The basic problem: "things change" requirements change -> design changes -> components change -> documentation changes Software configuration management: manages changes via versions. creates baselines. eliminates version skew.

3 Versioning 11:37 AM Versioning create a reference (version) number for each entire configuration. typical: Version 2.4 means major release 2, minor release 4. alternatively: Version is version 2 of the package, minor release 4, bug fix level 1. Conventional versioning: x.y.z where you change x when you make major changes to function. you change y when you add minor improvements you change z when you add bug fixes (no functional differences). Also find: x.y.z.w = major x, minor y, branch z, revision w. Releases major release number: denotes significant changes in function, e.g., new features. minor release number: denotes minor changes in function and/or bug fixes. Typically, between 2.3 and 2.4, the documentation doesn't change, while between 2.4 and 3.1, the documentation does change. Configuration Page 3

4 Version trees 11:46 AM Configurations form a version tree: Configuration Page 4

5 Configuration Page 5 Baselining 11:42 AM A baseline version of the software: serves as a basis and reference for further changes. has a simple version number, e.g., 2.0 and sometimes is fully tested and ready for release (whether actually released or not) has the property that all components are "in sync" as far as describing the same product.

6 Configuration Page 6 The "funnel" 3:32 PM baselining can be thought of as a funnel:

7 Version skew 11:34 AM Challenge of software configuration management: version skew happens when components must be updated together caller and callee component function and documentation component function and design or requirements A version skew occurs when two configuration items in one configuration refer to different versions of the product. Configuration Page 7

8 Configuration Page 8 Branches 11:50 AM version branches Normal development is a linear process: 1.0, 1.1, first version and fixes 2.0, 2.1, second version and fixes... A branch occurs when some entity requests an experimental or custom change. 1.2, (custom), , ,... Normal development continues, ignoring the branch

9 Configuration Page 9 Branch example 3:20 PM Branch example E.g., a commercial company requests a customization "just for them" Custom branches are a lucrative source of income in the open source/free software world. Custom branches can be merged into the main revision tree later, or orphaned if no one wants them anymore. Just because software is "free" doesn't mean programmers should be "poor"!

10 The Free Software Movement Simplified 3:21 PM Free software simplified Software is "free" if it cannot be charged for, its source is available to everyone, it cannot be incorporated into any product for which there is a charge. See the Gnu Public License. So, one cannot "pay" for free software. Justification for free software more people can work on it. more people can use it. more completely debugged and verified. Business model for free software Software itself is always free, but programmers' time is still worth money. So, pay programmers to customize free software support free software they've written write new free software In other words, custom branches feed programmers! Free versus open source Free software: source is available, free. Open source: source is available for people to review and change, but that may not be free. Configuration Page 10

11 Configuration Page 11 Version control 1:33 PM Version control refers to: ensuring that components change together when appropriate. constructing and maintaining new baselines managing changes to baselines ensuring an orderly progress from a change to its verification (through testing) tracking the state of a configuration as it is incrementally verified. Three concepts revision control: does a component change? version control: does a baseline change? change control: is a change reasonable?

12 Configuration Page 12 Tools rule! 1:39 PM Version control a human process with plenty of tools available to help. Main tools: revision control and version control.

13 Configuration Page 13 Revision control tools 1:44 PM Revision control tools maintain revision history for a single file. store changes, not contents. reverse-differential form: latest version plus changes needed to go backward. reference implementation: Revision Control System (RCS) Inside RCS: rcs -l file # lock a file so only you can change it. co file # get a copy of file co -u1.2 file # get a copy of revision 1.2 co -l file # get a copy and lock co -l2.3 file # get a copy of revision 2.3 and lock it. ci file # put a copy into the revision history ci -u file # put a copy and retain one for yourself ci -l file # put a copy and keep it locked rlog file # list revision history

14 RCS properties works on single files manages the state of a single file. very useful for prototyping! Configuration Page 14

15 Version control tools 1:45 PM Version control tools maintain revision history for a tree of files. use revision control on each file, in parallel. reference implementations: Concurrent Version System (CVS), SubVersion (SVN), etc. Inside CVS cvs checkout dir # check out a project cvs commit dir # check in a version cvs release dir # release a version cvs update dir # update files that have changed in repository Main differences between RCS and CVS: RCS CVS works on an individual file manages state of one file A word to the wise Storing a revision is really robust. Merging revisions is a dirty hack. works on a directory hierarchy manages state of the whole hierarchy as a unit Configuration Page 15

16 Configuration Page 16 Limits of version control 3:07 PM Limits of RCS/CVS/SVN version control designed around text files; versions of binary files are inefficient to record. line-oriented mechanisms for recording differences; does not work well with auto-formatting.

17 Configuration Page 17 More modern source control Wednesday, November 07, :00 PM More modern source control Web-based. Upon a subscription model. Source code is closed. (And/or the configuration is exceedingly complex) => web site can argue for a monopoly. Examples... github sourceforge codeplex

18 Configuration Page 18 Thinking more broadly... Wednesday, November 07, :19 AM Thinking more broadly, The configuration of a piece of software includes the things not written by you that are needed for it to run. External libraries External files. External components/programs.

19 Configuration Page 19 Basic principle of configuration Wednesday, November 07, :04 PM You can run, but you can't hide complexity. It goes somewhere. Into the software. Into the configuration.

20 Configuration Page 20 Deployment Wednesday, November 07, :21 AM Deployment: The process of creating a runnable copy of a software project. Input: a configuration for the software. Output: a runnable copy.

21 Configuration Page 21 Not just compilation... Wednesday, November 07, :22 AM Deployment is more than compilation... Are system requirements met? Check them. Are other components needed? Install them. Typical deployment path Compile a version of the software. Package the compiled files (without the sources) Install the package on the target computer.

22 Configuration Page 22 Packages and dependencies Wednesday, November 07, :21 AM Packages and dependencies A "package" is a distributable unit of software. Contains a mix of executable code, libraries, files. Can optionally contain source code. A "package manager" is software that installs and maintains packages. Defacto standard for linux: RedHat Package Manager (RPM). (file format used by many package managers) Several managers use the RPM format. Defacto package manager for windows: MIS Microsoft Software Installer format. Several competing formats for "installers"

23 Configuration Page 23 Inside RPM Wednesday, November 07, :24 AM Inside RPM A configuration file ('specfile'): Lists files to be packaged, and where to install them. Lists dependencies between packages, e.g., Package A REQUIRES Package B. Defines minimum versions for required packages. Creating an RPM package: Edit a specfile for the package. Invoke rpmbuild to create the package from source files. Distribute the package file created by rpmbuild. Using an RPM package The "rpm --install" command (or a number of variants): Looks up dependencies. Installs them if possible. Installs the package. Runs pre-install and post-install scripts, as needed.

24 Configuration Page 24 Windows software packages Wednesday, November 07, :33 AM Windows software packages Many third-party "installers". Microsoft standard: Windows Installer (.msi) files. Inside an.msi file: files to install. registry changes to make. scripts to run. Much simpler than RPMs: no dependency declarations.

25 Configuration Page 25 Repositories Wednesday, November 07, :28 AM Repositories A repository is a resource (usually web based) from which one can download packages. This is used to satisfy dependencies between packages.

26 Configuration Page 26 Challenges of package-based software deployment Wednesday, November 07, :29 AM Challenges of package-based software management Package conflicts: One RPM package requires gzip 1.2, the other requires gzip 1.0. Since requirements can't be co-resident, neither can the software. Cross-package corruption: RedHat packages can modify files from other packages without consent. MSI packages can modify the registry key for any other packages. These are common propagation vectors for spyware. Sequencing: Package installation must often be done in a specific order. E.g., install a language before installing a program written in that language, because that program's installer is written in that language (perl, python, etc) E.g., append contents to system files in a specific order. (RPM sequences installs according to dependencies declared in packages.)

27 Configuration Page 27 Social trends caused by packaging challenges Wednesday, November 07, :41 AM Social trends caused by packaging challenges Create special-purpose machines on which to install complex software. (e.g., for Cadence) Create virtual machines rather than installers; run as virtual instances under a host OS (e.g., Hadoop training machines)

Source Control. Comp-206 : Introduction to Software Systems Lecture 21. Alexandre Denault Computer Science McGill University Fall 2006

Source Control. Comp-206 : Introduction to Software Systems Lecture 21. Alexandre Denault Computer Science McGill University Fall 2006 Source Control Comp-206 : Introduction to Software Systems Lecture 21 Alexandre Denault Computer Science McGill University Fall 2006 Source Revision / Control Source Control is about the management of