GitOps Cookbook

Chapter 4. Kustomize

Deploying to a Kubernetes cluster is, in summary, applying some YAML files and checking the result.

The hard part is developing the initial YAML files version; after that, usually, they suffer only small changes such as updating the container image tag version, the number of replicas, or a new configuration value. One option is to make these changes directly in the YAML files—it works, but any error in this version (modification of the wrong line, deleting something by mistake, putting in the wrong whitespace) might be catastrophic.

For this reason, some tools let you define base Kubernetes manifests (which change infrequently) and specific files (maybe one for each environment) for setting the parameters that change more frequently. One of these tools is Kustomize.

In this chapter, you’ll learn how to use Kustomize to manage Kubernetes resource files in a template-free way without using any DSL.

The first step is to create a Kustomize project and deploy it to a Kubernetes cluster (see Recipe 4.1).

After the first deployment, the application is automatically updated with a new container image, a new configuration value, or any other field, such as the replica number (see Recipes 4.2 and 4.3).

If you’ve got several running environments (i.e., staging, production, etc.), you need to manage them similarly. Still, with its particularities, Kustomize lets you define a set of custom values per environment (see Recipe 4.4).

Application configuration values are properties ...