- [Instructor] Welcome back! In this lecture, we'll introduce you to the Jenkins Declarative Pipeline syntax. This syntax is perhaps less flexible, but provides a framework for laying out pipeline workflows in an opinionated manner and is quite useful for less complicated pipelines. 

Okay, let's begin. As already briefly mentioned, the declarative pipeline syntax aims to guide you through the process of building your own pipelines. It does so by providing a schema that controls the structure of the pipeline or, from an end user perspective, guides the pipeline author. As seen here in this screenshot, a declarative pipeline is composed of several optional and mandatory sections with some sections embedded in parent sections. A declarative pipeline always starts with a pipeline section, which in turn must contain an Agent and Stages section. The Stages section in turn contains multiple stage sections. Let's now take a quick look at what an actual stripped down basic vision of a declarative pipeline looks like as per the following example. 

Key points of this example are the syntax provides a guiding DSL structure that helps beginners to lay out and structure the pipeline. The script always starts with the pipeline keyword. Using the statement agent any tells Jenkins that the pipeline in all of its stages can be executed on any build agent. The pipeline is composed of three individual stages, build, test and deploy. Each stage may consist of one or many build steps, and in this case, a single step exists per stage. 

Let's now take a closer look at a couple of real world examples using the declarative pipeline syntax. In the first example, we use a declarative pipeline to build a NodeJS application leveraging NPM to perform the core build, test and deployment. Key points within this pipeline script are the tools keyword is used to inform Jenkins how to install the NodeJS tooling on the build agent that the pipeline executes on. In this case, we would have preinstalled the NodeJS Jenkins plugin, and then preconfigured it within the Global Tool Configuration section informing Jenkins how to setup NodeJS tooling to give our pipeline script access to the NPM executable. 

The pipeline script is composed of 4 stages, cloning, dependencies, test, and deploy. The cloning stage performs a git clone of the project source code into the workspace allocated to the pipeline. Each remaining stage executes a corresponding NPM script command. 

In the next example, we again use a declarative pipeline, but this time to build a Java application, leveraging Maven to perform the core build, testing, and docker image packaging and publishing. Key points of this declarative pipeline script are the agent section dictates that the pipeline must execute on a build agent tagged with the docker label. The environment section sets up script variables used later in the pipeline script. The pipeline consists of two stages, build and publish. The build stage overrides and resets the agent that it must execute on, in this case, it leverages a Maven docker container. 

The build stage finishes by running the post section which captures all of the compiled JAR files located in the target subdirectory. Each discovered JAR file becomes a build artifact, which can be referenced in later stages within the same pipeline. The publish stage only executes if the current source control branch is the master branch as specified in the when section. 

Finally, the publish stage incorporates a multi-line step declaration, useful for elongated build scripts. Also, the multi-line build step utilizes string interpolation to reference the previously assigned Image and Version pipeline environment variables.

Okay, go ahead and close this lecture, and we'll see you shortly in the next one.