There are two ways we can achieve this with either nightly builds or continuous development. The first option is that our developers are developing throughout the day on their tasks and come to the end of the set day they push their changes to the source code repository. Then during the night we run our unit tests and build the software. This could be deemed as the old way to integrate all code.
The other option and the preferred way is that our developers are still committing their changes to source code, then when that code commit has been made there is a build process kicked off continuously.
The above methods mean that with distributed developers across the world we don't have a set time each day where we have to stop committing our code changes. This is where Jenkins comes in to act as that CI server to control those tests and build processes.
I know we are talking about Jenkins here but I also want to add a few more to maybe look into later on down the line to get an understanding of why I am seeing Jenkins as the overall most popular, why is that and what can the others do over Jenkins.
- Bamboo - Can run multiple builds in parallel for faster compilation, built-in functionality to connect with repositories and has build tasks for Ant, and Maven.
- Buildbot - is an open-source framework for automating software build, test and release processes. It is written in Python and supports distributed, parallel execution of jobs across multiple platforms.
- Apache Gump - Specific to Java projects, designed to build and test those Java projects every night. ensures that all projects are compatible at both API and functionality levels.
Because we are now going to focus on Jenkins - Jenkins is again open source like all of the above tools and is an automation server written in Java. It is used to automate the software development process via continuous integration and facilitates continuous delivery.
**Extensible** - In addition to the Plug-Ins available, Jenkins can be extended by that plugin architecture which provides nearly infinite options for what it can be used for.
**Distributed** - Jenkins easily distributes work across multiple machines, helping to speed up builds, tests and deployments across multiple platforms.
You are going to be committing code to Jenkins, which then will build out your application, with all automated tests, it will then release and deploy that code when each step is completed. Jenkins is what allows for the automation of this process.
First up and not wanting to reinvent the wheel, the [Jenkins Documentation](https://www.jenkins.io/doc/developer/architecture/) is always the place to start but I am going to put down my notes and learnings here as well.
Jenkins can be installed on many different operating systems, Windows, Linux and macOS but then also the ability to deploy as a Docker container and within Kubernetes. [Installing Jenkins](https://www.jenkins.io/doc/book/installing/)
As we get into this we will likely take a look at installing Jenkins within a minikube cluster simulating the deployment to Kubernetes. But this will depend on the scenarios we put together throughout the rest of the section.
Step 3 - A build server then builds the code into an executable, in this example, we are using maven as a well-known build server. Another area to cover.
Step 5 - Jenkins then deploys the build app to the test server, in this example, we are using selenium as a well-known test server. Another area to cover.
There is a lot more to the architecture of Jenkins if you require it, they have a master-slave capability, which enables a master to distribute the tasks to the slave Jenkins environment.
For reference with Jenkins being open source, there are going to be lots of enterprises that require support, CloudBees is that enterprise version of Jenkins that brings support and possibly other functionality for the paying enterprise customer.
An example of this in a customer is Bosch, you can find the Bosch case study [here](https://assets.ctfassets.net/vtn4rfaw6n2j/case-study-boschpdf/40a0b23c61992ed3ee414ae0a55b6777/case-study-bosch.pdf)
I am going to be looking for a step-by-step example of an application that we can use to walk through using Jenkins and then also use this with some other tools.
