Job chaining in Jenkins is the process of automatically starting other job(s) after the execution of a job. This approach lets you build multi-step automation pipelines or trigger the rebuild of a project if one of its dependencies is updated. In this article, we will look at a couple of plugins for Jenkins job chaining and see how to use them to build and visualize these pipelines.
Out of the box solution – Build Other Projects
Jenkins has a built-in feature to build other projects. It is in the Post-build Actions section. You can specify the projects that you want to build after this project is built (you can trigger more than one). So whenever project A is built you will trigger the building of project B. You can also specify the conditions when the other jobs are built. Most often you are interested in continuing with the pipeline only if the job is successful but your mileage might vary.
One thing to remember here is that this feature has two configuration location. You can configure project A and specify a post action as in the previous screenshot. Another option is to configure this from project B and say “build this project B only after project A is built”. You don’t have to fill out both, just change one and the other is updated. See the next screenshot for the second option.
Build Pipeline Plugin
Build Pipeline Plugin is one interesting plugin. The main features of this plugin is to provide visualization of the pipeline and also to provide manual trigger for continuous delivery purposes. The configuration is a separate Post Build action where you can configure which projects should be built after project A. By default the triggering is actually done manually by the end user! If you want certain steps of the pipeline to be automatic then you have to use the built-in job chaining (see the Out of the Box Solution for more details).
The pipeline plugin offers a very good visualization of the pipeline. By configuring a new Jenkins view and choosing which job is the first job in the pipeline you can get a visualization of the whole pipeline. In the screenshot, be sure to note that one of those steps is manual and the result are automatic. The manual one can be triggered from the very same view.
Parameterized Trigger Plugin
The Parameterized Trigger Plugin is another triggering plugin but with a twist: this plugin lets you configure more aspects of the triggering logic. It covers the basic Out of the Box Solution features and adds many more. The most important one is the option to trigger the next build with parameters. For example, by defining SOURCE_BUILD_NUMBER=${BUILD_NUMBER} you are able to use the variable $SOURCE_BUILD_NUMBER in project B. This way you can, for example, use the artifact built in the previous job to be fetched from your central artifact repository using the ${BUILD_NUMBER}.
Downstream Buildview Plugin
The Downstream Buildview Plugin plugin that does not do job chaining itself, but provides a means to visualize the pipeline. Similar to the Build Pipeline View but more dynamic. You can click on any item in the build history and have its pipeline visualized.
Conclusions
The main feature that makes Jenkins so good is that there is always an app plugin for what you need. Of course, the same fact also highlights its biggest weakness. It is rather difficult to choose the correct plugin and very often you need a couple of plugins to achieve your goal. The same is true for job chaining and visualization.
The job chaining features that we covered in this post all provide the minimum functionality – triggering other jobs. The Parameterized Trigger plugin is the most feature-rich, but lacks the manual triggering. The Build Pipeline only offers manual triggering and you need to figure out automatic triggering yourself (using the built-in feature for example).
From the visualization side, the Build Pipeline plugin is definitely the best looking. At the same time, the plugin does not support passing parameters (the latest alpha build is a bit better) and once the pipeline gets long it gets a bit ugly. We do like the part of defining a separate view and then always being on top of your pipeline. The Downstream Build View plugin gives you great flexibility and insight to job chaining, but does not enforce any kind of process.
So, there are the Jenkins plugins that we use at ZeroTurnaround for job chaining and visualization. DO you use the same tools? If not, can you recommend any others? Which are your favorites? Please leave comments below!
