We will begin thisÂ chapter with an overview of the two primary software development methodologies of the era: Waterfall, and agile. An understanding of their concepts and implications will help us answer how Continuous Integration (CI) came into existence.
Next, we will try to understand the concept behind CI and the elements that make it. Reading through the topics, you will see how CI helps projects go agile. After completing this chapter, you should be able to:
- Describe how CI came into existence.
- Define what CI is.
- Describe the elements of CI.
The Software Development Life Cycle, also sometimes referred to as SDLC for short, is the process of planning, developing, testing, and deploying software.
Teams follow a sequence of phases, and each phase uses the outcome of its previous phase, as shown inÂ the following diagram:
Software Development Life Cycle
Let's take a look at the SDLC phases in detail.
This is the first stage of the cycle. Here, the business team (mostly comprised of business analysts) perform a requirement analysis of their project's business needs. The requirements can be internal to the organization, or external, from a customer. This study involves finding the nature and scope of the requirements. With the gathered information, there is a proposal to either improve the system or create a new one. The project cost gets decided, and benefits are laid out. Then the project goals are defined.
The second phase is the design phase. Here, the system architects and the system designers formulate the desired features of the software solution and create a project plan. This plan may include process diagrams, overall interface, and layout design, along with a vast set of documentation.
The third phase is the implementation phase. Here, the project manager creates and assigns work to the developers. The developers develop the code depending on the tasks and goals defined in the design phase. This phase may last from a few months to a year, depending on the project.
The fourth phase is the testing phase. When all the decided features are developed, the testing team takes over. For the next few months, all features are thoroughly tested. Every module of the software is collected and tested. Defects are raised if any bugs or errors occur while testing. In the event of a failure, the development team quickly acts to resolve the failures. The thoroughly tested code is then deployed into the production environment.
One of the most famous and widely used software development processes is the Waterfall model. The Waterfall model is a sequential software development process. It was derived from the manufacturing industry. One can see a highly structured flow of processes that run in one direction. At the time of its creation, there were no other software development methodologies, and the only thing the developers could have imagined was the production line process that was simple to adapt for software development.
The following diagram illustrates the Waterfall model of software development:
The Waterfall approach is simple to understand, as the steps involved are similar to that of the SDLC.
First, there is a requirement analysis phase, which is followed by the designing phase. There is a considerable time spent on the analysis and the designing part. And once it's over, there are no further additions or deletions. In short, once the development begins, there is no modification allowed in the design.
Then comes the implementation phase, where the actual development takes place. The development cycle can range from three months to six months. During this time, the testing team is usually free. When the development cycle is completed, a whole week's time is planned for performing the integration of the source code. During this time, many integration issues pop up and are fixed immediately. ThisÂ stage is followed by the testing phase.
When the testing starts, it goes on for another three months or more, depending on the software solution. After the testing completes successfully, the source code is then deployed in the production environment. For this, a day or so is again planned to carry out the deployment in production. There is a possibility that some deployment issues may pop up. When the software solution goes live, teams get feedback and may also anticipate issues.
The last phase is the maintenance phase. Feedback from the users/customers is analyzed, and the whole cycle of developing, testing, and releasing new features and fixes in the form of patches or upgrades repeats.
There is no doubt that the Waterfall model worked remarkably for decades. However, flaws did exist, but they were simply ignored for a long time. Since, way back then software projects had ample time and resources to get the job done.
However, looking at the way software technologies have changed over the past few years, we can easily say that the Waterfall model won't suit the requirements of the current world.
The following are some of the disadvantages of the Waterfall model:
- Working software is produced only at the end of the SDLC, which lasts for a year or so in most cases.
- There is a huge amount of uncertainty.
- It is not suitable for projects where the demand for new features is too frequent. For example, e-commerce projects.
- Integration is performed only after the entire development phase is complete. As a result, integration issues are found at a much later stage and in large quantities.
- There is no backward traceability.
- It's difficult to measure progress within stages.
By looking at the disadvantages of the Waterfall model, we can say that it's mostly suitable for projects where:
- The requirements are well documented and fixed.
- There is enough funding available to maintain a management team, a testing team, a development team, a build and release team, a deployment team, and so on.
- The technology is fixed, and not dynamic.
- There are no ambiguous requirements. And most importantly, they don't pop up during any other phase apart from the requirement analysis phase.
The name Agile rightly suggests quick and easy. Agile is a collection of methods where software is developed through collaboration among self-organized teams. The principles behind agile are incremental, quick, flexible software development, and it promotes adaptive planning.
The Agile software development process is an alternative to the traditional software development processes discussed earlier.
- Customer satisfaction through early and continuous delivery of useful software.
- Welcome changing requirements, even late in development.
- Working software is frequently delivered (in weeks, rather than months).
- Close daily cooperation between businesses, people, and developers.
- Projects are built around motivated individuals, who should be trusted.
- Face-to-face conversation is the best form of communication (co-location).
- Working software is the principal measure of progress.
- Sustainable developmentâable to maintain a constant pace.
- Continuous attention to technical excellence and good design.
- Simplicityâthe art of maximizing the amount of work not doneâis essential.
- Self-organizing teams.
- Regular adaptation to changing circumstances.
To know more about the Agile principles visit the link:Â http://www.agilemanifesto.org.
The twelve principles of Agile software development indicate the expectations of the current software industry and its advantages over the Waterfall model.
In the Agile software development process, the whole software application is split into multiple features or modules. These features are delivered in iterations. Each iteration lasts for three weeks, and involves cross-functional teams that work simultaneously in various areas, such as planning, requirement analysis, designing, coding, unit testing, and acceptance testing.
As a result, no person sits idle at any given point in time. This is quite different from the Waterfall model wherein while the development team is busy developing the software, the testing team, the production team, and everyone else is idle or underutilized. The following diagram illustrates the Agile model of software development:
From the preceding diagram,Â we can see that there is no time spent on requirement analysis or design. Instead, a very high-level plan is prepared, just enough to outline the scope of the project.
The team then goes through a series of iterations. Iteration can be classified as time frames, each lasting for a month or even a week in some mature projects. In this duration, a project team develops and tests features. The goal is to develop, test, and release a feature in a single iteration. At the end of the iteration, the feature goes for a demo. If the clients like it, then the feature goes live. But, if it gets rejected, the feature is taken as a backlog, re-prioritized, and again worked upon in the consecutive iteration.
There is also a possibility of parallel development and testing. In a single iteration, one can develop and test more than one feature in parallel.
- Functionality can be developed and demonstrated rapidly: In an agile process, the software project is divided by features, and each feature is called as a backlog. The idea is to develop either a single or a set of features right from its conceptualization till its deployment, in a week or a month. This puts at least a feature or two on the customer's plate, which they can then start using.
- Resource requirement is less: In Agile, there are no separate development and testing teams. Neither is there a build or release team, or a deployment team. In Agile, a single project team contains around eight members. Each member of the team is capable of doing everything.
- Promotes teamwork and cross-training: Since there is a small team of about eight members, the team members switch their roles in turns and learn from each other's experience.
- Suitable for projects where requirements frequently change: In an Agile model of software development, the complete software is divided into features, and each feature is developed and delivered in a short time span. Hence, changing the feature, or even completely discarding it, doesn't affect the whole project.
- Minimalistic documentation: This methodology focuses primarily on delivering working software quickly, rather than creating huge documents. Documentation exists, but it's limited to the overall functionality.
- Little or no planning required: Since features are developed one after the other in a short period, there is no need for extensive planning.
- Parallel development: Iteration consists of one or more features developed in sequence, or even in parallel.
Scrum is a framework for developing and sustaining complex products that are based on the Agile software development process. It is more than a process; it's a framework with certain roles, tasks, and teams. Scrum was written by Ken SchwaberÂ and Jeff Sutherland; together, they created The Scrum Guide.
In a Scrum framework, the development team decides on how to develop a feature. This is because the team knows best about the problem they are presented with. I assume most of the readers are happy after reading this.
Scrum relies on a self-organizing and cross-functional team. The Scrum team is self-organizing; hence, there is no overall team leader who decides which person will do which task, or how a problem will be solved.
- The Sprint: Sprint is a timebox during which a usable and potentially releasable productÂ gets created. A new Sprint starts immediately after the conclusion of the previous Sprint. A Sprint may last between two weeks to one month, depending on the project's command over Scrum.
- Product Backlog: The Product Backlog is a list of all the required features in a software solution. The list is dynamic. That is, now and then the customers or team members add or delete items to the Product Backlog.
- Sprint Backlog: The Sprint Backlog is the set of Product Backlog items, selected for the Sprint.
- Increment: The Increment is the sum of all the Product Backlog items completed during a Sprint and the value of the Increments from all the previous Sprints.
- The Development Team: The Development Team does the work of delivering a releasable set of features named Increment at the end of each Sprint. Only members of the Development Team create the Increment. Development Teams are empowered by the organization to organize and manage their work. The resulting synergy optimizes the Development Team's overall efficiency and effectiveness.
- The Product Owner: The Product Owner is a mediator between the Scrum Team and everyone else. He is the front face of the Scrum Team and interacts with customers, infrastructure teams, admin teams, everyone involved in the Scrum, and so on.
- The Scrum Master: The Scrum Master is responsible for ensuring Scrum is understood and enacted. Scrum Masters do this by ensuring that the Scrum Team follows the Scrum theory, practices, and rules.
Let us see some of the important aspects of the Scrum software development process that the team goes through.
Sprint Planning is an opportunity for the Scrum Team to plan the features in the current Sprint cycle. The plan is created mainly by the developers. Once the plan is created, it is explained to the Scrum Master and the Product Owner. The Sprint Planning is a timeboxed activity, and it is usually around eight hours in total for a one-month Sprint cycle. It is the responsibility of the Scrum Master to ensure everyone participates in the Sprint Planning activity.
In the meeting, the Development Team takes into consideration the following items:
- The number of Product Backlogs to be worked on (both new and the old ones from the last Sprint).
- Team performances in the last Sprint.
- Projected capacity of the Development Team.
During the Sprint cycle, the developers simply work on completing the backlogs decided in the Sprint Planning. The duration of a Sprint may last from two weeks to one month, depending on the number of backlogs.
This happens on a daily basis. During the Scrum meeting, the Development Team discusses what was accomplished yesterday, and what will be accomplished today. They also discuss the things that are stopping them from achieving their goal. The Development Team does not attend any other meeting or discussion apart from the Scrum meeting.
The Daily Scrum is a good opportunity for a team to measure its progress. The Scrum Team can track the total work remaining, and byÂ doing so, they can estimate the likelihood of achieving the Sprint Goal.
In the Sprint Review, the Development Team demonstrates the features that have been accomplished. The Product Owner updates on the Product Backlog status to date. The Product Backlog list is updated depending on the product performance or usage in the market. Sprint Review is a four-hour activity altogether for a one-month Sprint.
In this meeting, the team discusses the things that went well, and the things that need improvement. The team then decides the points on which it has to improve to perform better in the upcoming Sprint. This meeting usually occurs after the Sprint Review and before the Sprint Planning.
Integration is the act of submitting your private work (modified code) to the common work area (the potential software solution). This is technically done by merging your private work (personal branch) with the common work area (Integration branch). Or we can say, pushing your private branch to the remote branch.
CI is necessary to bring out issues encountered during the integration as early as possible. This can be understood from the following diagram, which depicts various issues encountered during a single CI cycle.
A build failure can occur due to either an improper code or a human error while doing a build (assuming that the tasks are done manually). An integration issue can occur if the developers do not rebase their local copy of code frequently with the code on the Integration branch. A testing issue can occur if the code does not pass any of the unit or integration test cases.
In the event of an issue, the developer has to modify the code to fix it:
Developing a feature involves many code changes, and between every code change, there are a set of tasks to perform, such as checking-in the code, polling the version control system for changes, building the code, unit testing, integration, building on the integrated code, integration testing, and packaging. In a CI environment, all these steps are made fast and error-free by using a CI tool such asÂ Jenkins.Â
Adding notifications makes things even faster. The sooner the team members are aware of a build, integration, or deployment failure, the quicker they can act.Â The following diagram depicts all theÂ steps involved in a CI process:
CI process with notifications
In this way, the team quickly moves from feature to feature. In simple terms, the agilityÂ of the agile software development is greatly due to CI.
The amount of code written for the embedded systems presents inside a car is more than the one present inside a fighter jet. In today's world, embedded software is inside every product, modern or traditional. Be it cars, TVs, refrigerators, wrist watches, or bikes; all have little or more software-dependent features. Consumer products are becoming smarter day by day. Nowadays, we can see a product being marketed more using its smart and intelligent features than its hardware capabilities. For example, an air conditioner is marketed by its wireless control features, and TVs are being marketed by their smart features, like embedded web browsers, and so on.
The need to market new products has increased the complexity of products. This increase in software complexity had brought the Agile software development and CI methodologies to the limelight, though there were times when agile software development was used by a team of no more than 30-40 people that were working on a simple project. Almost all types of projects benefit from CI: mostly the web-based projects, for example, the e-commerce websites, and mobile phone apps.
CI and agile methodologies are used in projects that are based on Java, .NET, Ruby on Rails, and every other programming language present today. The only place where you will see it not being used is in the legacy systems. However, even they are going agile. Projects based on SAS, Mainframes; all are trying to benefit from CI.
This is the most basic and the most important requirement for implementing CI. A Version Control System, sometimes also called a Revision Control System, is a tool to manage your code history. It can be centralized or distributed. Some of the famous centralized version control systems are SVN and IBM Rational ClearCase. In the distributed segment, we have tools like GIT and Mercurial.
Ideally, everything that is required to build software must be version controlled. A version control tool offers many features, such as tagging, branching, and so on.
When using a Version Control System, keep the branching to a minimum. A few companies have only one main branch, and all the development activity happens on that. Nevertheless, most of the companies follow some branching strategies. This is because there is always a possibility that a part of the team may work on one release, while others may work on another release. Other times, there is a need to support the older release versions. Such scenarios always lead companies to use multiple branches.
GitFlow is another way of managing your code using multiple branches. In the following method, the Master/Production branch is kept clean and contains only the releasable, ready-to-ship code. All the development happens on the Feature branches, with the Integration branch serving as a common place to integrate all the features. The following diagram is a moderate version of the GitFlow:
The following diagramÂ illustrates the full version of GitFlow. We have a Master/Production branch that contains only the production-ready code. The Feature branches are where all of the development takes place. The Integration branch is where the code gets integrated and tested for quality. In addition to that, we have release branches that are pulled out from the Integration branch as and when there is a stable release. All bug fixes related to a release happen in the Release branches. There is also a Hotfix branch that is pulled out of the Master/Production branch as and when there is a need for a hotfix:
GitFlow branching strategy
What is a CI tool? Well, it is nothing more than an orchestrator. A CI tool is at the center of the CIÂ system, connected to the Version Control System, build tools, Binary Repository Manager tool, testing and production environments, quality analysis tool, test automation tool, and so on. There are many CI tools: Build Forge, Bamboo, and TeamCity, to name a few. But the prime focus of our book is Jenkins:
Centralized CI server
A CI tool providesÂ options to create pipelines. Each pipeline has its own purpose. There are pipelines to take care of CI. Some take care of testing; some take care of deployments, and so on. Technically, a pipeline is a flow of jobs. Each job is a set of tasks that run sequentially. Scripting is an integral part of a CIÂ tool that performs various kinds of tasks. The tasks may be as simple as copying a folder/file from one location to the other, or they can be complex Perl scripts to monitor machines for file modifications. Nevertheless, the script is getting replaced by the growing number of plugins available in Jenkins. Now you need not script to build a Java code; there are plugins available for it. All you need to do is install and configure a plugin to get the job done. Technically, plugins are nothing but small modules written in Java. They remove the burden of scripting from the developer's head. We will learn more about pipelines in the upcoming chapters.
The next important thing to understand is the self-triggered automated build. Build automation is simply a series of automated steps that compile the code and generate executables. The build automation can take the help of build tools like Ant and Maven. The self-triggered automated build is the most important part of a CI system. There are two main factors that call for an automated build mechanism:
- Catching integration or code issues as early as possible.
There are projects where 100 to 200 builds happen per day. In such cases, speed plays an important factor. If the builds are automated, then it can save a lot of time. Things become even more interesting if the triggering of the build is made self-driven, without any manual intervention. Auto-triggered build on every code change further saves time.
When builds are frequent and fast, the probability of finding an error (build error, compilation error, or integration error) in the framework of SDLC is higher and faster:
Probability of error versus build graph
Type of coverage
The number of functions called out of the total number of functions defined
The number of statements in the program that are truly called out of the total number
The number of branches of the control structures executed
The number of Boolean sub-expressions that are being tested for a true and a false value
The number of lines of source code that are being tested out of the total number of lines present inside the code
Types of code coverage
This coverage percentage is calculated by dividing the number of items tested by the number of items found. The following screenshot illustrates the code coverage report fromÂ SonarQube:
Code coverage report on SonarQube
Static code analysis, also commonly called white-boxÂ testing, is a form of software testing that looks for the structural qualities of the code. For example, it answers how robust or maintainable the code is. Static code analysis is performed without actually executing programs. It is different from the functional testing, which looks into the functional aspects of software, and is dynamics.
Static code analysis is the evaluation of software's inner structures. For example, is there a piece of code used repetitively? Does the code contain lots of commented lines? How complex is the code? Using the metrics defined by a user, an analysis report is generated that shows the code quality regarding maintainability. It doesn't question the code's functionality.
Some of the static code analysis tools like SonarQube come with a dashboard, which shows various metrics and statistics of each run. Usually, as part of CI, the static code analysis is triggered every time a build runs. As discussed in the previous sections, static code analysis can also be included before a developer tries to check-in his code. Hence, a code of low quality can be prevented right at the initial stage.
Static code analysis report
Static code analysis report
Testing is an important part of an SDLC. To maintain quality software, it is necessary that the software solution goes through various test scenarios. Giving less importance to testing can result in customer dissatisfaction and a delayed product.
Since testing is a manual, time-consuming, and repetitive task, automating the testing process can significantly increase the speed of software delivery. However, automating the testing process is a bit more difficult than automating the build, release, and deployment processes. It usually takes a lot of effort to automate nearly all the test cases used in a project. It is an activity that matures over time.
Hence, when beginning to automate the testing, we need to take a few factors into consideration. Test cases that are of great value and easy to automate must be considered first. For example, automate the testing where the steps are the same, although they run with different data every time. Further, automate the testing where software functionality is tested on various platforms. Also, automate the testing that involves a software application running with different configurations.
Previously, the world was mostly dominated by desktop applications. Automating the testing of a GUI-based system was quite difficult. This called for scripting languages where the manual mouse and keyboard entries were scripted and executed to test the GUI application. Nevertheless, today the software world is completely dominated by web and mobile-based applications, which are easy to test through an automated approach using a test automation tool.
Once a code is built, packaged, and deployed, testing should run automatically to validate the software. Traditionally, the process followed is to have an environment for SIT, UAT, PT, and pre-production. First, the release goes through SIT, which stands for system integration testing. Here, testing is performed on an integrated code to check its functionality altogether. If the integration testing is passed, the code is deployed to the next environment, which is UAT, where it goes through user acceptance testing, and then it can lastly be deployed in PT, where it goes through performance testing. In this way, the testing is prioritized.
It is not always possible to automate all the testing. But, the idea is to automate whatever testing that is possible. The preceding method discussed requires the need to have many environments and also a higher number of automated deployments into various environments. To avoid this, we can go for another method where there is only one environment where the build is deployed, and then the basic tests are run, and after that, long-running tests are triggered manually.
As part of the SDLC, the source code is continuously built into binary artifacts using CI. Therefore, there should be a place to store these built packages for later use. The answer is, using a binary repository tool. But what is a binary repository tool?
A binary repository tool is a Version Control System for binary files. Do not confuse this with the Version Control System discussed in the previous sections. The former is responsible for versioning the source code, and the latter is for binary files, such as
.msi, and so on. Along with managing built artifacts, a binary repository tool can also manage 3-party binaries that are required for a build. For example, the Maven plugin always downloads the plugins required to build the code into a folder. Rather than downloading the plugins again and again, they can be managed using a repository tool:
From the above illustration, you can see as soon as a build gets created and passes all the checks, the built artifact is uploaded to the binary repository tool. From here, the developers and testers can manually pick them, deploy them, and test them. Or, if the automated deployment is in place, then the built artifacts are automatically deployed to the respective test environment. So, what're the advantages of using a binary repository?
A binary repository tool does the following:
- Every time a built artifact gets generated, it is stored in a binary repository tool. There are many advantages of storing the build artifacts. One of the most important advantages is that the build artifacts are located in a centralized location from where they can be accessed when needed.
- It can store third-party binary plugins, modules that are required by the build tools. Hence, the build tool need not download the plugins every time a build runs. The repository tool is connected to the online source and keeps updating the plugin repository.
- It records what, when, and who created a build package.
- It provides a staging likeÂ environments to manage releases better. This also helps in speeding up the CI process.
- In a CIÂ environment, the frequency of build is too high, and each build generates a package. Since all the built packages are in one place, developers are at liberty to choose what to promote and what not to promote in higher environments.
There is a possibility that a build may have many components. Let's take, for example, a build that has aÂ
.rar file as an output. Along with that, it has some Unix configuration files, release notes, some executables, and also some database changes. All of these different components need to be together. The task of creating a single archive or a single media out of many components is called packaging. Again, this can be automated using the CI tools and can save a lot of time.
In contrast to this, integrating every single commit on your Feature branch with the Integration branch and testing it for issues (CI) allows you to find integration issues as early as possible.
Tools like Jenkins, SonarQube, Artifactory, and GitHub allow you to generate trends over a period. All of these trends can help project managers and teams to make sure the project is heading in the right direction and with the right pace.
This is the most important advantage of having a carefully implemented CI system. Any integration issue or merge issue gets caught early. The CI system has the facility to send notification as soon as the build fails.
From a technical perspective, CI helps teams work more efficiently. Projects that use CI follow an automatic and continuous approach while building, testing, and integrating their code. This results in a faster development.
Developers spend more time developing their code and zero time building, packaging, integrating, and deploying it, as everything is automated. This also helps teams that are geographically distributed to work together. With a good software configuration management process in place, people can work on widely distributed teams.
In the past, build and release activities were managed by the developers, along with the regular development work. It was followed by a trend of having separate teams that handled the build, release, and deployment activities. And it didn't stop there; this new model suffered from communication issues and a lack of coordination among developers, release engineers, and testers. However, using CI, all the build, release, and deployment work gets automated. Therefore, the development team need not worry about anything other than developing features. In most cases, even the complete testing is automated. Therefore byÂ using a CI process, the development team can spend more time developing the code.
"Behind every successful agile project, there is a Continuous Integration process."
In this chapter, we took a glance through the history of software engineering processes. We learned about CI and the elements that make it.
The various concepts and terminologies discussed in this chapter form a foundation for the upcoming chapters. Without these, the coming chapters are mere technical know-how.
In the next chapter, we will learn how to install Jenkins on various platforms.