repository·master·Indexed 11 days ago
https://github.com/kubernetes-sigs/kustomizeA tool for customizing raw, template-free YAML files for Kubernetes. It uses a base and overlay pattern to manage multiple environment configurations (such as dev, staging, and prod) by applying patches, name prefixes, and common labels to a common base without modifying original files.
The Kustomize repository is organized into several semantically versioned Go modules:
| Module | Purpose |
|---|---|
api | High-level Kustomize code suitable for import by other programs (e.g., kubectl). Contains krusty, filters, loader, and resmap |
kustomize | The main CLI entry point containing main.go and Cobra command implementations |
kyaml | A Kubernetes-focused enhancement of go-yaml used for low-level YAML manipulation and RNode handling |
cmd/config | Provides Unix-like file manipulation commands (like grep and tree) for Kubernetes YAML files |
kustomization.yaml file serves as the primary entry point for Kustomize execution. It defines the configuration, resources, and transformations (such as patches, generators, and transformers) that Kustomize should apply to a set of Kubernetes resources during the build process.Kustomize is a tool for customizing Kubernetes resource configurations without using templates or Domain Specific Languages (DSLs). It works by taking raw, template-free YAML files and applying customizations to them while leaving the original files untouched.
Key characteristics:
make, what Kustomize does is declared in a configuration file.sed, it emits edited text (YAML) based on the input and instructions.Kustomize processes a kustomization file in a specific sequence of stages. Understanding this order is critical for predicting how resources are modified:
resources: Kustomize reads the YAML files or hydrates recursive kustomizations to create the initial list of input objects.generators: Kustomize executes generators, adding the newly created KRM objects to the resource list.transformers: Kustomize applies transformers to modify, add, remove, or reorder the current list of objects.validators: Kustomize runs validators to check the final list for errors. Validators can fail the build but are intended to be non-mutating.A Validator Plugin is a specialized plugin type used to validate the resulting YAML output of a Kustomize build. Unlike transformers, validators are intended to inspect resources rather than modify them.
stdin. The plugin must write the validated resources to stdout. If no changes are needed, the plugin can print nothing to stdout.kustomization directory where it is being invoked.validated-by (case-sensitive) to the top-level resources. Any other modifications will cause Kustomize to throw an error.stderr output.You can implement validators using either an exec plugin (e.g., a bash script) or a Go plugin.
kustomize localize command is designed to download all remote resources referenced in a kustomization file and save them into a local directory. This allows a kustomization layer to become self-contained, making it possible to version control a fully localized directory without relying on external network calls during kustomize build.You can perform partial string replacements by splitting a field value and replacing a specific segment.
Use the options object within source or targets to configure this:
delimiter: The string used to split the field.index: The position in the split array to replace (default is 0).Behavioral Notes:
index is out of bounds, Kustomize throws an error.index is less than 0, the value is prefixed. If the index is beyond the length of the split, the value is suffixed.# If source value is 'path/to/VALUE'
options:
delimiter: '/'
index: 2
# Resulting target value: 'path/to/NEW_VALUE'Since version 3.2.0, Kustomize supports 'inline patches', allowing you to define patch content directly within the kustomization.yaml file as a single string using the |- YAML block scalar. This eliminates the need to manage separate patch files for simple modifications.
There are three primary ways to apply patches in a kustomization.yaml file:
patchesStrategicMerge: A list of patches parsed as Strategic Merge Patches.patchesJSON6902: A list of JSON Patches that must include an associated target. Each patch can only be applied to one target resource.patches: A flexible list of patches and their associated targets. Kustomize automatically detects whether the provided patch is a Strategic Merge Patch or a JSON Patch. This method allows a single patch to be applied to multiple objects.Kustomize does not support globbing (e.g., *.yaml) directly inside kustomization files during kustomize build. This prevents the configuration from depending on the local file system state in an undeclared way.
Instead, you should use kustomize edit commands that accept globbed arguments. These commands expand the globs at edit time relative to your local file system and write the resulting explicit filenames into the kustomization file. This preserves the requirement that all resources are explicitly declared in version control.
A patchStrategicMerge (SMP) is a strategic-merge-style patch that uses an incomplete YAML specification of a Kubernetes resource. It includes TypeMeta fields (group, version, kind, name) to identify the target resource, followed by the specific fields you wish to change (e.g., an image tag).
Key Behaviors:
replace (the default)deleteKustomize manages changes to the kustomization.yaml schema using the following rules: