Continuous Software Development (Media Engineering Architecture & Deployment)

# Continuous Software Development

Learn about continuous integration, continuous testing, continuous delivery and continuous deployment.

This material is part of [architecture & deployment course](https://github.com/MediaComem/comem-archidep) for [Media Engineering](https://heig-vd.ch/formations/bachelor/filieres/ingenierie-des-medias).

**Recommended reading**

* [Collaborating with Git](../git-collaborating/)

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## What is continuous software development?

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### Continuous et al.

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Continuous software development is an umbrella term that describes several aspects of [**iterative software development**][iterative]:

* [**C**ontinuous **I**ntegration (CI)][ci]
* [**C**ontinuous **T**esting (CT)][ct]
* [**C**ontinous **D**elivery (CDE)][cde]
* [**C**ontinous **D**eployment (CD)][cd]

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### The waterfall model

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Iterative development is a solution to the problems of the earlier **waterfall model** of software development.
In this model, progress flows in largely one direction through the phases of conception, design, implementation, verification and maintenance.

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The idea came from the manufacturing and construction industries,
and was initially applied to software development.

However, it makes it **difficult to respond to changes in requirements**.
If you are already in the verification phase, it's too late for new design and implementation.

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### Iterative software development

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In contrast, iterative software development consists in developing software through **repeated cycles** (iterations) and in smaller portions at a time (incrementally).

The planning, analysis, implementation, testing and evaluation **phases are repeated at each iteration** throughout the project.

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#### Advantages of iterative software development

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The main advantages of developing iteratively are:

* **User involvement:** the customer is involved at each and every iteration for planning and requirements,
  which makes it much easier to identify problems and react to changes in requirements.
* **Human resources:** less staff is required compared to the waterfall model.
* **Time limitation:** the first iterations can potentially be delivered within weeks while a waterfall project usually takes months.

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### Agile software development

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[**Agile software development**][agile] is one of the most popular iterative development models.

It was popularized by the [Manifesto for Agile Software Development][agile-manifesto]
which describes the values and principles espoused by the model.
It has been adopted by many software development companies to improve the quality and speed of software.

There are various [agile frameworks][agile-frameworks] you can use to organize your work.
Each has a slightly different focus:

* [eXtreme Programming (XP)][xp] (focus on practices)
* [Kanban][kanban] (focus on workflow)
* [Scrum][scrum] (focus on workflow)

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### What is continuous software development, again?

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To use agile software development or other iterative development models,
you **must be able to move and react quickly**.

Hence these various so-called "continuous" practices which help achieve this:

Practice                                  | Description
:---                                      | :---
[**C**ontinuous **I**ntegration (CI)][ci] | Regularly merge developer work to a shared mainline to avoid "integration hell".
[**C**ontinuous **T**esting (CT)][ct]     | Automate testing to reduce feedback waiting time for developers.
[**C**ontinous **D**elivery (CDE)][cde]   | Automate software delivery so that it can be reliably released at any time.
[**C**ontinous **D**eployment (CD)][cd]   | Automate software deployment to regularly provide new features to users.

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## Continuous Integration (CI)

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[**C**ontinuous **I**ntegration (CI)][ci] is the practice of merging all developer work to a shared mainline regularly,
instead of having each developer work independently for days or weeks on end, and suffering when the time comes to integrate their work back into the mainline.

This is often managed with [version control][vcs] systems such as [Git][git].
A software development team may define a [workflow][git-workflows] determining when to merge work back into the mainline
(typically the `master` branch).

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## Continuous Testing (CT)

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[**C**ontinuous **T**esting (CT)][ct] is the practice of using automated tests
to obtain immediate feedback while developing instead of waiting for the Quality Assurance (QA) engineers to manually test the software.

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Software such as websites or mobile applications have traditionally been tested manually.
However, it **takes time to go through all possible paths** through an application and make sure it works.
Every time code changes, someone potentially broke something that a manual tester might fail to notice.

**Tests can be automated by writing them in code,**
increasing their speed and avoiding boring and repetitive click work for manual testers.

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Automated tests are often integrated into the continuous pipeline by running them automatically
every time changes are pushed to **version control**.

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## Continuous delivery (CDE)

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[**C**ontinous **D**elivery (CDE)][cde] is the practice of ensuring that software can be reliably released at any time,
usually by automating the building, testing and releasing of software.
This is often called a **deployment pipeline**.

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## Continuous deployment (CD)

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[**C**ontinous **D**eployment (CD)][cd] is one step further than [**C**ontinous **D**elivery (CDE)][cde]:
also automating the deployment of the software in addition to its delivery.

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## Continuous software development

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To recap, continuous software development is the practice of regularly
integrating, testing, delivering and deploying software, usually through automation.

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There are many tools to help you do this.
These are just a few examples:

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## References

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* [Iterative development][iterative] vs. [Waterfall model][waterfall]
  * [Agile Software Development][agile]: [Kanban][kanban], [Scrum][scrum], [eXtreme Programming][xp]
* [Continuous Integration][ci]
  * [Git Workflows][git-workflows]
     * [A Successful Git Branching Model][git-model]
     * [A Successful Git Branching Model Considered Harmful][git-model-harmful]
* [Continuous Testing][ct]
* [Continous Delivery][cde]
* [Continous Deployment][cd]

[agile]: https://en.wikipedia.org/wiki/Agile_software_development
[agile-frameworks]: https://en.wikipedia.org/wiki/Agile_software_development#Agile_software_development_methods
[agile-manifesto]: https://agilemanifesto.org/
[cd]: https://en.wikipedia.org/wiki/Continuous_deployment
[cde]: https://en.wikipedia.org/wiki/Continuous_delivery
[ci]: https://en.wikipedia.org/wiki/Continuous_integration
[codacy]: https://www.codacy.com/
[ct]: https://en.wikipedia.org/wiki/Continuous_testing
[git]: https://git-scm.com/
[gitlab-ci]: https://about.gitlab.com/product/continuous-integration/
[git-model]: https://nvie.com/posts/a-successful-git-branching-model/
[git-model-harmful]: https://barro.github.io/2016/02/a-succesful-git-branching-model-considered-harmful/
[git-workflows]: https://git-scm.com/book/en/v2/Git-Branching-Branching-Workflows
[iterative]: https://en.wikipedia.org/wiki/Iterative_and_incremental_development
[jenkins]: https://jenkins.io/
[kanban]: https://en.wikipedia.org/wiki/Kanban_(development)
[scrum]: https://en.wikipedia.org/wiki/Scrum_(software_development)
[travis]: https://jenkins.io/
[vcs]: https://en.wikipedia.org/wiki/Version_control
[waterfall]: https://en.wikipedia.org/wiki/Waterfall_model
[xp]: https://en.wikipedia.org/wiki/Extreme_programming