webhook

pkg/controller/webhook - Webhook Adapter Component

Event adapter component that bridges the pure webhook library to the controller architecture.

Overview

The webhook adapter manages the complete lifecycle of Kubernetes admission webhooks:

• TLS certificate generation and rotation
• HTTPS webhook server lifecycle
• Dynamic ValidatingWebhookConfiguration management
• Integration with controller event bus
• Bridging webhook validation to controller validators

This is a coordination layer - the actual webhook functionality lives in pkg/webhook (pure library).

Component Architecture

pkg/webhook/ (Pure Library)
    ├── CertificateManager
    ├── Server
    └── ConfigManager
         ↓
    wrapped by
         ↓
pkg/controller/webhook/ (Event Adapter)
    └── Component
         ├── Manages lifecycle
         ├── Publishes events
         └── Bridges to validators

Usage

Basic Setup

import (
    "haptic/pkg/controller/webhook"
    "haptic/pkg/webhook"
)

// Create component
webhookComponent := webhook.New(
    kubeClient,
    eventBus,
    logger,
    webhook.Config{
        Namespace:   "default",
        ServiceName: "my-webhook-svc",
        Rules: []webhook.WebhookRule{
            {
                APIGroups:   []string{""},
                APIVersions: []string{"v1"},
                Resources:   []string{"configmaps"},
            },
        },
    },
)

// Start component (blocks until context cancelled)
ctx, cancel := context.WithCancel(context.Background())
defer cancel()

go webhookComponent.Start(ctx)

Configuration

config := webhook.Config{
    // Required
    Namespace:   "default",
    ServiceName: "webhook-service",

    // Optional (defaults shown)
    WebhookConfigName: "haptic-webhook",
    Port:              9443,
    Path:              "/validate",
    CertRotationCheckInterval: 24 * time.Hour,

    // Validation rules
    Rules: []webhook.WebhookRule{
        {
            APIGroups:   []string{""},
            APIVersions: []string{"v1"},
            Resources:   []string{"configmaps"},
        },
    },
}

Graceful Shutdown

// Stop webhook component
if err := webhookComponent.Stop(ctx); err != nil {
    log.Error("Failed to stop webhook", "error", err)
}

Events Published

The component publishes events to the EventBus for observability and coordination:

Lifecycle Events

• WebhookServerStartedEvent: Server started successfully
• WebhookServerStoppedEvent: Server stopped

Certificate Events

• WebhookCertificatesGeneratedEvent: Initial certificates generated
• WebhookCertificatesRotatedEvent: Certificates rotated

Configuration Events

• WebhookConfigurationCreatedEvent: ValidatingWebhookConfiguration created
• WebhookConfigurationUpdatedEvent: ValidatingWebhookConfiguration updated

Validation Events

• WebhookValidationRequestEvent: Admission request received
• WebhookValidationAllowedEvent: Resource admitted
• WebhookValidationDeniedEvent: Resource rejected
• WebhookValidationErrorEvent: Validation error

Certificate Rotation

Certificates are automatically rotated when they approach expiration:

1. Periodic Check: Every 24 hours (configurable)
2. Rotation Threshold: 30 days before expiry (from certificate manager)
3. Rotation Process:
   • Generate new certificates
   • Update ValidatingWebhookConfiguration with new CA bundle
   • Restart server with new certificates
   • Publish rotation event

Integration with Controller

The webhook component is typically started in controller initialization:

// After config loaded and EventBus started
webhookComponent := webhook.New(kubeClient, eventBus, logger, webhookConfig)
go webhookComponent.Start(ctx)

Kubernetes Resources Required

Service

The webhook server needs a Kubernetes Service to receive requests from the API server:

apiVersion: v1
kind: Service
metadata:
  name: my-webhook-svc
  namespace: default
spec:
  selector:
    app: my-controller
  ports:
    - port: 443
      targetPort: 9443
      protocol: TCP

RBAC

The controller needs permissions to manage ValidatingWebhookConfiguration:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: webhook-manager
rules:
  - apiGroups: ["admissionregistration.k8s.io"]
    resources: ["validatingwebhookconfigurations"]
    verbs: ["get", "create", "update", "patch", "delete"]

Troubleshooting

Webhook Not Receiving Requests

Check:

1. Service exists and selects correct pods
2. ValidatingWebhookConfiguration exists
3. CA bundle matches generated CA certificate
4. Network policies allow API server → webhook traffic

Debug:

# Verify service
kubectl get svc my-webhook-svc -o yaml

# Verify webhook configuration
kubectl get validatingwebhookconfigurations my-webhook -o yaml

# Check webhook server logs
kubectl logs deployment/my-controller | grep webhook

Certificate Errors

Symptoms: x509: certificate signed by unknown authority

Fix: Ensure CA bundle in ValidatingWebhookConfiguration matches the CA certificate used to sign server certificate.

Check:

# View CA bundle
kubectl get validatingwebhookconfigurations my-webhook \
    -o jsonpath='{.webhooks[0].clientConfig.caBundle}' | base64 -d

Port Conflicts

Symptoms: address already in use

Fix: Change webhook port in configuration or verify no other process uses port 9443.

Advanced Topics

Custom Validation

To wire webhook to existing validators (Phase 2 feature):

// Create validator bridge
func (c *Component) createValidator(gvk string) webhook.ValidationFunc {
    return func(obj interface{}) (bool, string, error) {
        // Publish validation request event
        req := events.NewConfigValidationRequest(obj)

        // Use request-response pattern to gather validation results
        result, err := c.eventBus.Request(ctx, req, events.RequestOptions{
            Timeout: 5 * time.Second,
            ExpectedResponders: []string{"basic", "template"},
        })

        // Aggregate results
        if err != nil || !allValid(result) {
            return false, extractReason(result), nil
        }

        return true, "", nil
    }
}

Multiple Webhook Rules

Define separate rules for different resource types:

Rules: []webhook.WebhookRule{
    {
        APIGroups:   []string{""},
        APIVersions: []string{"v1"},
        Resources:   []string{"configmaps"},
        Operations:  []admissionv1.OperationType{admissionv1.Create, admissionv1.Update},
    },
    {
        APIGroups:   []string{""},
        APIVersions: []string{"v1"},
        Resources:   []string{"secrets"},
        Operations:  []admissionv1.OperationType{admissionv1.Create},
    },
}

Failure Policy

Control what happens when webhook is unavailable:

// Fail-closed (reject requests if webhook down)
fail := admissionv1.Fail
rule.FailurePolicy = &fail

// Fail-open (allow requests if webhook down)
ignore := admissionv1.Ignore
rule.FailurePolicy = &ignore

See Also

• Pure webhook library: pkg/webhook/README.md
• Webhook event types: pkg/controller/events/README.md
• Controller architecture: docs/development/design.md