The road from a source file to a Service

At the end of Part 2 , the cluster in our VM could run any image that somebody had already built and published, as it did with the nginx web server. The step that remains is the one every enterprise developer takes many times a day, which is turning code they have just written into something the cluster can run, and that step is less a single leap than a chain of small transformations. Source code becomes a JAR file, the JAR becomes a container image, the image is pushed to a registry, the cluster pulls it to start pods, and a Service routes requests to those pods. Figure 1 draws the chain.

Figure 1. The path from source code to a running Service, in which Maven turns the code into a JAR, Docker turns the JAR into an image and pushes it to the registry, and Kubernetes starts two pods from the image behind a NodePort Service, with a check available after each link.

Each link in that chain can be checked on its own, as the line beneath the figure reminds us.…