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Kubebuilder Annotation

If you have been using Kubebuilder, you must have seen comments such as // +kubebuilder:rbac: .... , // +kubebuilder:resource:... in scaffolder Go files. These special comments are used by kubebuilder tools (controller-tools) to generate CRD, RBAC, webhook manifests. In kubebuilder, these special comments are Kubebuilder Annotation, a.k.a annotation. It is designed for this kind of use case: To use kubebuilder tools, all you have to do is focus on writing your code, and put instructions with parameters as annotations along with your code, so that everything will be handled based on these annotations instructions by kubebuilder. This document illustrates the syntax of these annotations.

Kubebuilder Annotation Syntax

Kubebuilder Annotation has a series of tokens separated by colons into groups from left to right. Each Token is a string identifier in an annotation instance. It has meaning by its position in token slice, in the form of +[header]:[module]:[submodule]:[key-value elements] Go Annotation starts with + (e.g. // +kubebuilder) to differentiate from regular go comments.

Token types

  • header is the identifier of a group of annotations. It helps user know which project provides this annotation. For example, in Kubernetes project, headers like kubebuilder, k8s, genclient, etc. are all project identifiers. A header is required for all annotations, since you may use multiple annotations from different projects in the same codebase.

  • module is the identifier of functional module in an annotation. An annotation may have a group of modules, each of which performs a particular function.

  • submodule (optional) In some cases, the module has a big functional scope, split into fine-grained sub modules, which provide the flexibility of extending module functionality. For example: module:submodule1:submodule2:submodule3 submodule can be multiple following one by one.

Levels of symbols

Delimiter symbols are distinguished to work in different levels from top-down for splitting values string in tokens, which provides readability and efficiency.

  • Colon

    Colon : is the 1st level delimiter (to annotation) only for separate tokens. Tokens on different sides of the colon should refer to different token types.

  • Comma

    Comma , is the 2nd level delimiter (to annotation) for splitting key-value pairs in key-value elements which is normally the last token in annotation. e.g. +kubebuilder:printcolumn:name=<name>,type=<type>,description=<desc>,JSONPath:<.spec.Name>,priority=<int32>,format=<format> It works within token which is the 2nd level of annotation, so it is called "2nd level delimiter"

  • Equal sign

    Equal sign = is the 3rd level delimiter (to annotation) for identifying key and value. Since the key=value parts are splitted from single token (2nd level), its inner delimiter = works for next level (3rd level)

  • Semicolon sign

    Semicolon sign ; is the 4th level delimiter, which works on the value part (4th level) of key=value(3rd level) for splitting individual values. e.g. key1=value1;value2;value3

  • Pipe sign or Vertical bar

    Pipe sign | is the 5th level delimiter, which works inside the single value part (4th level) indicating key and value in case of the single value has nested key-value structure. e.g. outerkey=innerkey1|innervalue1

Examples

Webhook annotation examples

[header] is kubebuilder, [module] is webhook, [submodule] is admission or serveroption

// +kubebuilder:webhook:admission:groups=apps,resources=deployments,verbs=CREATE;UPDATE,name=bar-webhook,path=/bar,type=mutating,failure-policy=Fail

// +kubebuilder:webhook:serveroption:port=7890,cert-dir=/tmp/test-cert,service=test-system|webhook-service,selector=app|webhook-server,secret=test-system|webhook-secret,mutating-webhook-config-name=test-mutating-webhook-cfg,validating-webhook-config-name=test-validating-webhook-cfg

Notes:

  1. Separate two submodule (categories) under webhook: 1) admissionand 2) serveroption, handling webhookTags and serverTags separately.
  2. For each submodule, all key-values should put in the same comment line.
  3. using | for splitting key-value of lables

RBAC Annotation examples

[header] is kubebuilder [module] is rbac No submodule at this moment, support annotations like : // +rbac, // +kubebuilder:rbac

// +kubebuilder:rbac:groups=apps,resources=deployments,verbs=get;list;watch;delete

// +rbac:groups=apps,resources=deployments,verbs=get;list;watch;delete