[book] webhook manifest generator

docs/book/SUMMARY.md

@@ -41,6 +41,7 @@
 * Webhooks
   * [What is a Webhook](beyond_basics/what_is_a_webhook.md)
   * [Webhook Example](beyond_basics/sample_webhook.md)
+  * [Webhook Configuration Installation](beyond_basics/webhook_installer_generator.md)
 * Client-Go
   * [Generated Informers](beyond_basics/using_client_go_informers.md)
 * Deployment Workflow

docs/book/beyond_basics/sample_webhook.md

@@ -124,6 +124,7 @@ A Server registers Webhook Configuration with the apiserver and creates an HTTP
 The server is behind a Kubernetes Service and provides a certificate to the apiserver when serving requests.
 
 The Server depends on a Kubernetes Secret containing this certificate to be mounted under `CertDir`.
+The Secret needs to present but not have to be prepopulated before the manager pod starts. 
 
 If the Secret is empty, during bootstrapping the Server will generate a certificate and write it into the Secret.
 

docs/book/beyond_basics/webhook_installer_generator.md

@@ -0,0 +1,150 @@
+# Webhook Configuration Installation
+
+Installing webhook configurations requires higher privileges which manager's service account might not have.
+In that case, a separate process with higher privileges would like to install the webhook configurations.
+
+There are 2 options to install webhook configurations into a cluster:
+
+- Configure the Webhook Server to automatically install the webhook configurations when it starts.
+- Use the webhook manifests generator to generate webhook configurations.
+Then install the webhook configurations and deploy the webhook servers.
+
+## Webhook Installer
+
+Webhook installer is a feature provided by the [controller-runtime](https://godoc.org/sigs.k8s.io/controller-runtime/pkg/webhook) library.
+For a [Webhook Server](https://godoc.org/sigs.k8s.io/controller-runtime/pkg/webhook#Server),
+you can choose to enable the webhook installer.
+Depending on your [ServerOptions](https://godoc.org/sigs.k8s.io/controller-runtime/pkg/webhook#ServerOptions),
+the installer may install [mutatingWebhookConfigurations](https://github.com/kubernetes/api/blob/9fcf73cc980bd64f38a4f721a7371b0ebb72e1ff/admissionregistration/v1beta1/types.go#L113-L124),
+[validatingWebhookConfigurations](https://github.com/kubernetes/api/blob/9fcf73cc980bd64f38a4f721a7371b0ebb72e1ff/admissionregistration/v1beta1/types.go#L83-L94)
+and service; it may also update the secret if needed.
+
+To make the webhook installer work correctly, please ensure the manager's service account has
+the right permissions. For example. it may need permissions:
+- create and update MutatingWebhookConfigurations and ValidatingWebhookConfigurations
+- create and update the Service in the same namespace of the manager
+- update the Secret in the same namespace of the manager
+
+The service fronts the webhook server.
+So please ensure the service's selectors select your webhook server pods.
+
+The secret contains
+- the serving certificate and its corresponding private key
+- the signing CA certificate and its corresponding private key
+
+Webhook installer can be very helpful for
+- faster iteration during development
+- easier deployment in production if policy allows
+
+Webhook installer is on by default. Set
+[`DisableWebhookConfigInstaller`](https://github.com/kubernetes-sigs/controller-runtime/blob/a8ea2056444a5d74d7408e4b8798cbe63b14066b/pkg/webhook/server.go#L57-L60)
+to true to turn it off.
+
+## Webhook Manifests Generator
+
+From cluster administrators perspective, they may want to have the webhook configurations
+installation to be a separate process from running the webhook server,
+since permissions to create and update webhook configurations are considered as high privileges.
+
+Similar to other generators in [controller-tools](https://github.com/kubernetes-sigs/controller-tools),
+webhook manifest generator is annotation-driven.
+
+How the webhook manifest generator works
+1) It parses the annotations to configure
+[Webhook](https://godoc.org/sigs.k8s.io/controller-runtime/pkg/webhook/admission#Webhook).
+1) It parses the annotations to configure
+[ServerOptions](https://godoc.org/sigs.k8s.io/controller-runtime/pkg/webhook#ServerOptions).
+1) It uses the library in controller-runtime, which is the same machinery as
+the installer, to generate the webhook configuration manifests.
+
+#### Comment Group
+
+A comment group represents a sequence of comments with no empty lines between.
+Comment group is a concept that is important for writing and parsing annotations correctly.
+
+For example, the following comments are in one comment group
+
+```
+// +kubebuilder:webhook:groups=apps
+// +kubebuilder:webhook:resources=deployments
+```
+
+The following comments are in 2 comments groups
+
+```
+// +kubebuilder:webhook:groups=apps
+
+// +kubebuilder:webhook:resources=deployments
+```
+
+#### Annotations
+
+Each comment line that starts with `+kubebuilder:webhook:` will be processed to extract annotations.
+
+The annotations can be grouped in 2 categories based on what struct they configure.
+
+The _first_ category is for each individual webhook.
+They are used to set the fields in [`Webhook`](https://github.com/kubernetes-sigs/controller-runtime/blob/a8ea2056444a5d74d7408e4b8798cbe63b14066b/pkg/webhook/admission/webhook.go#L55-L80) struct.
+The annotations for the same webhook are allowed to span across multiple lines as long as they are prefixed with
+`+kubebuilder:webhook:` and in the __same__ comment group.
+It is suggested to put this category of annotations in the same file as its corresponding webhook.
+
+For example, the following is for one single webhook
+
+```
+// +kubebuilder:webhook:groups=apps,versions=v1,resources=deployments,verbs=create,update
+// +kubebuilder:webhook:name=mutating-create-update-deployment.testproject.org
+// +kubebuilder:webhook:path=/mutating-create-update-deployment
+// +kubebuilder:webhook:type=mutating,failure-policy=fail
+```
+
+`groups`, `versions` and `resources` have the same semantic as the ones used for generating RBAC manifests.
+They can reference a core type or a CRD type.
+
+`verbs` are used to set [`Operations`](https://github.com/kubernetes/api/blob/9fcf73cc980bd64f38a4f721a7371b0ebb72e1ff/admissionregistration/v1beta1/types.go#L234-L243).
+It supports `create`, `update`, `delete`, `connect` and `*` case-insensitively.
+
+`name` is the name of the webhook and
+is used to set [`Name`](https://github.com/kubernetes/api/blob/9fcf73cc980bd64f38a4f721a7371b0ebb72e1ff/admissionregistration/v1beta1/types.go#L146).
+`path` is the endpoint that this webhook serves and
+is used to set [`Path`](https://github.com/kubernetes-sigs/controller-runtime/blob/a8ea2056444a5d74d7408e4b8798cbe63b14066b/pkg/webhook/admission/webhook.go#L61-L62).
+Both `name` and `path` do NOT allow `,` and `;`.
+
+`type` indicates the webhook type which can be either `mutating` or `validating`.
+
+`failure-policy` is used to set [`FailurePolicy`](https://github.com/kubernetes/api/blob/9fcf73cc980bd64f38a4f721a7371b0ebb72e1ff/admissionregistration/v1beta1/types.go#L54-L61).
+It supports `fail` and `ignore` case-insensitively.
+
+The _second_ category is for the webhook server.
+All of them are used to configuration [`ServerOptions`](https://github.com/kubernetes-sigs/controller-runtime/blob/a8ea2056444a5d74d7408e4b8798cbe63b14066b/pkg/webhook/server.go#L39-L98) struct.
+Each annotation should only be used once.
+They don't have to be in the same comment group.
+It is suggested to put this category of annotations in the same file as the webhook server.
+
+The following is an example using webhook server annotations.
+
+```
+// +kubebuilder:webhook:port=7890,cert-dir=/path/to/cert
+// +kubebuilder:webhook:service=test-system:webhook-service,selector=app:webhook-server
+// +kubebuilder:webhook:secret=test-system:webhook-secret
+// +kubebuilder:webhook:mutating-webhook-config-name=test-mutating-webhook-cfg
+// +kubebuilder:webhook:validating-webhook-config-name=test-validating-webhook-cfg
+```
+
+`port` is the port that the webhook server serves. It is used to set [`Port`](https://github.com/kubernetes-sigs/controller-runtime/blob/a8ea2056444a5d74d7408e4b8798cbe63b14066b/pkg/webhook/server.go#L43).
+
+`service` should be formatted as `<namespace>:<name>`. It is used to set
+[the name and namespace of the service](https://github.com/kubernetes-sigs/controller-runtime/blob/a8ea2056444a5d74d7408e4b8798cbe63b14066b/pkg/webhook/server.go#L102-L105).
+
+`selector` should be formatted as `key1:value1;key2:value2` and it has 2 usages:
+- use as [selectors in the service](https://github.com/kubernetes-sigs/controller-runtime/blob/a8ea2056444a5d74d7408e4b8798cbe63b14066b/pkg/webhook/server.go#L106-L108)
+- use as additional labels that will be added to field `.spec.template.metadata.labels` of
+the StatefulSet through [`kustomize`](https://github.com/kubernetes-sigs/kustomize).
+
+`host` is used to set [`Host`](https://github.com/kubernetes-sigs/controller-runtime/blob/a8ea2056444a5d74d7408e4b8798cbe63b14066b/pkg/webhook/server.go#L87-L91).
+
+`secret` should be formatted as `<namespace>:<name>`. It is used to set [`Secret`](https://github.com/kubernetes-sigs/controller-runtime/blob/a8ea2056444a5d74d7408e4b8798cbe63b14066b/pkg/webhook/server.go#L73-L77)
+
+`mutating-webhook-config-name` is used to set [`MutatingWebhookConfigName`](https://github.com/kubernetes-sigs/controller-runtime/blob/a8ea2056444a5d74d7408e4b8798cbe63b14066b/pkg/webhook/server.go#L68-L69).
+
+`validating-webhook-config-name` is used to set [`ValidatingWebhookConfigName`](https://github.com/kubernetes-sigs/controller-runtime/blob/a8ea2056444a5d74d7408e4b8798cbe63b14066b/pkg/webhook/server.go#L70-L71).