Introduction to Software Engineering/Tools/Continuous Integration

Software Development with Continuous Integration We can make a much more comprehensive book on the subject In software engineering, continuous integration (CI) implements continuous processes of applying quality control — small pieces of effort, applied frequently. Continuous integration aims to improve the quality of software, and to reduce the time taken to deliver it, by replacing the traditional practice of applying quality control after completing all development. Theory When embarking on a change, a developer takes a copy of the current code base on which to work. As other developers submit changed code to the code repository, this copy gradually ceases to reflect the repository code. When developers submit code to the repository they must first update their code to reflect the changes in the repository since they took their copy. The more changes the repository contains, the more work developers must do before submitting their own changes. Eventually, the repository may become so different from the developers' baselines that they enter what is sometimes called "integration hell",Cunningham Ward Ward Cunningham Integration Hell WikiWikiWeb 05 Aug 2009 http://c2.com/cgi/wiki?IntegrationHell 19 Sept 2009 where the time it takes to integrate exceeds the time it took to make their original changes. In a worst-case scenario, developers may have to discard their changes and completely redo the work. Continuous integration involves integrating early and often, so as to avoid the pitfalls of "integration hell". The practice aims to reduce rework and thus reduce cost and time. The rest of this article discusses best practice in how to achieve continuous integration, and how to automate this practice. Automation is a best practice itself. Brauneis David David Brauneis [OSLC] Possible new Working Group - Automation open-services.net Community 01 January 2010 http://open-services.net/pipermail/community_open-services.net/2010-January/000214.html 16 February 2010 Taylor Bradley Bradley Taylor http://blog.railsmachine.com/articles/2009/02/10/rails-deployment-and-automation-with-shadowpuppet-and-capistrano/ Rails Deployment and Automation with ShadowPuppet and Capistrano Taylor, Rails Deployment and Automation with ShadowPuppet and Capistrano Recommended practices Continuous integration - as the practice of frequently integrating one's new or changed code with the existing code repository - should occur frequently enough that no intervening window remains between commit and build, and such that no errors can arise without developers noticing them and correcting them immediately.http://martinfowler.com/articles/continuousIntegration.html#PracticesOfContinuousIntegration Continuous Integration 2009-11-11 Fowler Martin Martin Fowler Normal practice is to trigger these builds by every commit to a repository, rather than a periodically scheduled build. The practicalities of doing this in a multi-developer environment of rapid commits are such that it's usual to trigger a short timer after each commit, then to start a build when either this timer expires, or after a rather longer interval since the last build. Automated tools such as CruiseControl or Hudson offer this scheduling automatically. Another factor is the need for a version control system that supports atomic commits, i.e. all of a developer's changes may be seen as a single commit operation. There is no point in trying to build from only half of the changed files. Maintain a code repository This practice advocates the use of a revision control system for the project's source code. All artifacts required to build the project should be placed in the repository. In this practice and in the revision control community, the convention is that the system should be buildable from a fresh checkout and not require additional dependencies. Extreme Programming advocate Martin Fowler also mentions that where branching is supported by tools, its use should be minimised March 2010. Instead, it is preferred that changes are integrated rather than creating multiple versions of the software that are maintained simultaneously. The mainline (or trunk) should be the place for the working version of the software. Automate the build A single command should have the capability of building the system. Many build-tools, such as make, have existed for many years. Other more recent tools like Ant, Maven, MSBuild or IBM Rational Build Forge are frequently used in continuous integration environments. Automation of the build should include automating the integration, which often includes deployment into a production-like environment. In many cases, the build script not only compiles binaries, but also generates documentation, website pages, statistics and distribution media (such as Windows MSI files, RPM or DEB files). Make the build self-testing Once the code is built, all tests should run to confirm that it behaves as the developers expect it to behave. Everyone commits to the baseline every day By committing regularly, every committer can reduce the number of conflicting changes. Checking in a week's worth of work runs the risk of conflicting with other features and can be very difficult to resolve. Early, small conflicts in an area of the system cause team members to communicate about the change they are making. Many programmers recommend committing all changes at least once a day (once per feature built), and in addition performing a nightly build. Every commit (to baseline) should be built The system should build commits to the current working version in order to verify that they integrate correctly. A common practice is to use Automated Continuous Integration, although this may be done manually. For many, continuous integration is synonymous with using Automated Continuous Integration where a continuous integration server or daemon monitors the version control system for changes, then automatically runs the build process. Keep the build fast The build needs to complete rapidly, so that if there is a problem with integration, it is quickly identified. Test in a clone of the production environment Having a test environment can lead to failures in tested systems when they deploy in the production environment, because the production environment may differ from the test environment in a significant way. However, building a replica of a production environment is cost prohibitive. Instead, the pre-production environment should be built to be a scalable version of the actual production environment to both alleviate costs while maintaining technology stack composition and nuances. Make it easy to get the latest deliverables Making builds readily available to stakeholders and testers can reduce the amount of rework necessary when rebuilding a feature that doesn't meet requirements. Additionally, early testing reduces the chances that defects survive until deployment. Finding errors earlier also, in some cases, reduces the amount of work necessary to resolve them. Everyone can see the results of the latest build It should be easy to find out where/whether the build breaks and who made the relevant change. Automate deployment Most CI systems allow the running of scripts after a build finishes. In most situations, it is possible to write a script to deploy the application to a live test server that everyone can look at. A further advance in this way of thinking is Continuous Deployment, which calls for the software to be deployed directly into production, often with additional automation to prevent defects or regressionsSee Continuous deployment in 5 easy steps - O'Reilly Radar and Continuous Deployment at IMVU: Doing the impossible fifty times a day. - Timothy Fitz. History Continuous Integration emerged in the Extreme Programming (XP) community, and XP advocates Martin Fowler and Kent Beck first wrote about continuous integration circa 1999. Fowler's paperFowler Martin Martin Fowler http://www.martinfowler.com/articles/continuousIntegration.html Continuous Integration Fowler, Continuous Integration is a popular source of information on the subject. Beck's book Extreme Programming ExplainedExtreme Programming Explained Beck Kent Kent Beck 1999 0-201-61641-6 Beck, Extreme Programming Explained, the original reference for Extreme Programming, also describes the term. Advantages and disadvantages Advantages Continuous integration has many advantages: when unit tests fail or a bug emerges, developers might revert the codebase back to a bug-free state, without wasting time debugging developers detect and fix integration problems continuously - avoiding last-minute chaos at release dates, (when everyone tries to check in their slightly incompatible versions). early warning of broken/incompatible code early warning of conflicting changes immediate unit testing of all changes constant availability of a "current" build for testing, demo, or release purposes immediate feedback to developers on the quality, functionality, or system-wide impact of code they are writing frequent code check-in pushes developers to create modular, less complex codeNovember 2009 metrics generated from automated testing and CI (such as metrics for code coverage, code complexity, and features complete) focus developers on developing functional, quality code, and help develop momentum in a teamNovember 2009 Disadvantages initial setup time required well-developed test-suite required to achieve automated testing advantages large-scale refactoring can be troublesome due to continuously changing code base hardware costs for build machines can be significant Many teams using CI report that the advantages of CI well outweigh the disadvantages. Jared Richardson Agile Testing Strategies at No Fluff Just Stuff Conference http://www.nofluffjuststuff.com Boston, Massachusetts September 2008 The effect of finding and fixing integration bugs early in the development process saves both time and money over the lifespan of a project. Software To support continuous integration, software tools such as automated build software can be employed. Software tools for continuous integration include: AnthillPro — continuous integration server by Urbancode Apache Continuum — continuous integration server supporting Apache Maven and Apache Ant. Supports CVS, Subversion, Ant, Maven, and shell scripts Apache Gump — continuous integration tool by Apache Automated Build Studio — proprietary automated build, continuous integration and release management system by AutomatedQA Bamboo — proprietary continuous integration server by Atlassian Software Systems BuildBot — Python/Twisted-based continuous build system BuildForge - proprietary automated build engine by IBM / Rational BuildMaster — proprietary application lifecycle management and continuous integration tool by Inedo CABIE - Continuous Automated Build and Integration Environment — open source, written in Perl; works with CVS, Subversion, AccuRev, Bazaar and Perforce Cascade — proprietary continuous integration tool; provides a checkpointing facility to build and test changes before they are committed codeBeamer — proprietary collaboration software with built-in continuous integration features CruiseControl — Java-based framework for a continuous build process CruiseControl.NET — .NET-based automated continuous integration server CruiseControl.rb - Lightweight, Ruby-based continuous integration server that can build any codebase, not only Ruby, released under Apache Licence 2.0 ElectricCommander — proprietary continuous integration and release management solution from Electric Cloud FinalBuilder Server — proprietary automated build and continuous integration server by VSoft Technologies Go — proprietary agile build and release management software by Thoughtworks Jenkins (formerly known as Hudson) — MIT-licensed, written in Java, runs in servlet container, supports CVS, Subversion, Mercurial, Git, StarTeam, Clearcase, Ant, NAnt, Maven, and shell scripts Software Configuration and Library Manager — software configuration management system for z/OS by IBM Rational Software QuickBuild - proprietary continuous integration server with free community edition featuring build life cycle management and pre-commit verification. TeamCity — proprietary continuous-integration server by JetBrains with free professional edition Team Foundation Server — proprietary continuous integration server and source code repository by Microsoft Tinderbox — Mozilla-based product written in Perl Rational Team Concert — proprietary software development collaboration platform with built-in build engine by IBM including Rational Build Forge See comparison of continuous integration software for a more in depth feature matrix. Further reading Paul M. Duvall Paul Duvall 2007 Continuous Integration. Improving Software Quality and Reducing Risk Addison-Wesley 0-321-33638-0 References 30em External links Comparison of continuous integration software Continuous integration by Martin Fowler (an introduction) Continuous Integration at the Portland Pattern Repository (a collegial discussion) Cross platform testing at the Portland Pattern Repository Continuous Integration Server Feature Matrix (a guide to tools) Continuous Integration: The Cornerstone of a Great Shop by Jared Richardson (an introduction) A Recipe for Build Maintainability and Reusability by Jay Flowers Continuous Integration anti-patterns by Paul Duvall Extreme programming