Given that we already explored continuous deployment, you might be wondering why are we even talking at this point about continuous delivery. There are a few reasons for that. First of all, I am conscious that many of you will not or can not implement continuous deployment. Your tests might not be as reliable as you'd need them to be. Your processes might not allow full automation. You might have to follow regulations that prevent you from reaching nirvana. There could be many other reasons. The point is that not everyone can apply continuous deployment. Even among those that can get there, there are indeed some that do not want that as the destination. So, we'll explore continuous delivery as an alternative to continuous deployment.

There are other reasons for writing this chapter. So far, I showed you one possible implementation of the continuous deployment pipeline. We could modify the existing pipeline by adding an input step before making the release and upgrading production. That would add proceed and cancel buttons that we could use to choose whether to upgrade the production release or not. This chapter would be the shortest chapter ever, and that would be boring. Where's the fun in doing a small variation of the same?

We'll use this chapter to explore a few alternative approaches to writing Jenkins pipeline. Just as the pipeline from the previous chapter could be easily converted from continuous deployment to continuous delivery process, what we're going to do next could also go both ways. So, even though our objective is to write a continuous delivery pipeline, the lessons from this chapter could be easily applied to continuous deployment as well.

We'll use this opportunity to explore declarative pipeline as an alternative to scripted. We'll switch from using a separate VM for building docker image to using the Docker socket to build it in one of the nodes of the cluster. We'll explore how we can define our whole productions environment differently. We'll even introduce GitOps.

The real goal is to give you valid alternatives to the approaches we used so far, thus allowing you to make better decisions when implementing lessons-learned in your organization. I hope that by the end of this chapter you will be able to cherry-pick things that suit you the best and assemble your own process.

That's it for the prep-talk. You know what continuous delivery is, and you know how to use Kubernetes. Let's define some pipelines.