kacerr/gatewayapi-certificates-operator
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feat: initial implementation of gateway-cert-operator

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Kubernetes operator that automates HTTPS listener configuration on
Gateway API Gateway resources whenever a cert-manager Certificate is
created or updated.

Core behaviour:
- Watches cert-manager Certificate resources for the annotation
  gateway-cert-operator.io/gateway-name to identify the target Gateway
- Builds HTTPS listeners (prefixed "auto-") from each Certificate's
  DNS SANs and merges them into the target Gateway's listener list
- Preserves any manually-managed listeners; removes stale auto-listeners
  when Certificates are deleted or their annotations are removed
- Supports optional annotations to override the target namespace and
  listener port (default 443)

Components:
- main.go                            – manager setup, scheme registration,
                                       health/readiness probes
- internal/controller/               – Certificate reconciler with field
                                       indexing and dual-watch pattern
- internal/gateway/patch.go          – listener construction, merge, and
                                       equality helpers
- deploy/manifests.yaml              – Namespace, RBAC, and Deployment
- docs/README.md                     – usage guide and architecture notes
- Dockerfile                         – distroless multi-stage build

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
Jan Novak
2026-03-26 10:54:33 +01:00
commit a78e4421ef
9 changed files with 814 additions and 0 deletions
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154
internal/controller/certificate_controller.go Normal file
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package controller
import (
"context"
"fmt"
cmv1 "github.com/cert-manager/cert-manager/pkg/apis/certmanager/v1"
"k8s.io/apimachinery/pkg/types"
ctrl "sigs.k8s.io/controller-runtime"
"sigs.k8s.io/controller-runtime/pkg/client"
"sigs.k8s.io/controller-runtime/pkg/handler"
"sigs.k8s.io/controller-runtime/pkg/log"
"sigs.k8s.io/controller-runtime/pkg/reconcile"
gwapiv1 "sigs.k8s.io/gateway-api/apis/v1"
gw "github.com/example/gateway-cert-operator/internal/gateway"
)
const (
// AnnotationGatewayName is the annotation key specifying which Gateway to update.
AnnotationGatewayName = "gateway-cert-operator.io/gateway-name"
// AnnotationGatewayNamespace optionally overrides the Gateway namespace. Defaults to Certificate namespace.
AnnotationGatewayNamespace = "gateway-cert-operator.io/gateway-namespace"
// AnnotationListenerPort optionally overrides the listener port. Defaults to 443.
AnnotationListenerPort = "gateway-cert-operator.io/listener-port"
// ListenerPrefix is prepended to managed listener names so we can distinguish ours.
ListenerPrefix = "auto-"
// IndexFieldGatewayTarget is the field index for mapping Certificates to their target Gateway.
IndexFieldGatewayTarget = ".metadata.annotations.gatewayTarget"
)
// CertificateReconciler reconciles Certificate objects and patches Gateway listeners.
type CertificateReconciler struct {
client.Client
}
// SetupCertificateReconciler creates the reconciler and registers watches.
func SetupCertificateReconciler(mgr ctrl.Manager) error {
r := &CertificateReconciler{Client: mgr.GetClient()}
// Index Certificates by their target Gateway so we can list all certs for a given Gateway.
if err := mgr.GetFieldIndexer().IndexField(context.Background(), &cmv1.Certificate{}, IndexFieldGatewayTarget, func(obj client.Object) []string {
cert := obj.(*cmv1.Certificate)
gwName, ok := cert.Annotations[AnnotationGatewayName]
if !ok {
return nil
}
gwNs := cert.Annotations[AnnotationGatewayNamespace]
if gwNs == "" {
gwNs = cert.Namespace
}
return []string{fmt.Sprintf("%s/%s", gwNs, gwName)}
}); err != nil {
return fmt.Errorf("failed to setup field index: %w", err)
}
return ctrl.NewControllerManagedBy(mgr).
For(&cmv1.Certificate{}).
// Secondary watch: if someone edits the Gateway, re-reconcile relevant Certificates.
Watches(&gwapiv1.Gateway{}, handler.EnqueueRequestsFromMapFunc(r.gatewayToCertificates)).
Complete(r)
}
// Reconcile handles Certificate create/update/delete events.
func (r *CertificateReconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Result, error) {
log := log.FromContext(ctx)
var cert cmv1.Certificate
if err := r.Get(ctx, req.NamespacedName, &cert); err != nil {
// Certificate deleted — we still need to reconcile the Gateway.
// We can't know which Gateway it targeted anymore, so we rely on the
// fact that the index query below will simply not return this cert,
// and the Gateway will be patched without its listener.
// To handle this properly, we reconcile ALL Gateways that had any
// managed listener. In practice, deletion triggers the index update,
// and the Gateway watch re-enqueues the right certs.
return ctrl.Result{}, client.IgnoreNotFound(err)
}
gwName, ok := cert.Annotations[AnnotationGatewayName]
if !ok {
log.V(1).Info("certificate missing gateway annotation, skipping")
return ctrl.Result{}, nil
}
gwNamespace := cert.Annotations[AnnotationGatewayNamespace]
if gwNamespace == "" {
gwNamespace = cert.Namespace
}
// List ALL certificates targeting this Gateway so we compute the full desired state.
var certList cmv1.CertificateList
if err := r.List(ctx, &certList, client.MatchingFields{
IndexFieldGatewayTarget: fmt.Sprintf("%s/%s", gwNamespace, gwName),
}); err != nil {
return ctrl.Result{}, fmt.Errorf("listing certificates for gateway %s/%s: %w", gwNamespace, gwName, err)
}
// Build desired listeners from all annotated certificates.
desiredListeners := gw.BuildListenersFromCertificates(certList.Items, ListenerPrefix)
// Fetch the target Gateway.
var gateway gwapiv1.Gateway
if err := r.Get(ctx, types.NamespacedName{Name: gwName, Namespace: gwNamespace}, &gateway); err != nil {
return ctrl.Result{}, fmt.Errorf("getting gateway %s/%s: %w", gwNamespace, gwName, err)
}
// Merge: keep non-prefixed listeners, replace all auto-* listeners.
updated := gw.MergeListeners(gateway.Spec.Listeners, desiredListeners, ListenerPrefix)
if gw.ListenersEqual(gateway.Spec.Listeners, updated) {
log.V(1).Info("gateway listeners already up to date")
return ctrl.Result{}, nil
}
patch := client.MergeFrom(gateway.DeepCopy())
gateway.Spec.Listeners = updated
if err := r.Patch(ctx, &gateway, patch); err != nil {
return ctrl.Result{}, fmt.Errorf("patching gateway %s/%s: %w", gwNamespace, gwName, err)
}
log.Info("patched gateway listeners",
"gateway", fmt.Sprintf("%s/%s", gwNamespace, gwName),
"managedListeners", len(desiredListeners),
)
return ctrl.Result{}, nil
}
// gatewayToCertificates maps a Gateway event back to all Certificates targeting it.
func (r *CertificateReconciler) gatewayToCertificates(ctx context.Context, obj client.Object) []reconcile.Request {
gw := obj.(*gwapiv1.Gateway)
key := fmt.Sprintf("%s/%s", gw.Namespace, gw.Name)
var certList cmv1.CertificateList
if err := r.List(ctx, &certList, client.MatchingFields{
IndexFieldGatewayTarget: key,
}); err != nil {
log.FromContext(ctx).Error(err, "listing certificates for gateway", "gateway", key)
return nil
}
requests := make([]reconcile.Request, 0, len(certList.Items))
for _, cert := range certList.Items {
requests = append(requests, reconcile.Request{
NamespacedName: types.NamespacedName{
Name: cert.Name,
Namespace: cert.Namespace,
},
})
}
return requests
}

155
internal/gateway/patch.go Normal file
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package gateway
import (
"fmt"
"sort"
"strings"
cmv1 "github.com/cert-manager/cert-manager/pkg/apis/certmanager/v1"
gwapiv1 "sigs.k8s.io/gateway-api/apis/v1"
)
var (
defaultPort gwapiv1.PortNumber = 443
tlsModeTerminate = gwapiv1.TLSModeTerminate
namespacesFromAll gwapiv1.FromNamespaces = gwapiv1.NamespacesFromAll
gatewayGroup gwapiv1.Group = gwapiv1.GroupName
gatewayKind gwapiv1.Kind = "Gateway"
)
// BuildListenersFromCertificates creates the desired set of managed listeners
// from all annotated Certificate resources targeting a single Gateway.
func BuildListenersFromCertificates(certs []cmv1.Certificate, prefix string) []gwapiv1.Listener {
var listeners []gwapiv1.Listener
for _, cert := range certs {
if cert.DeletionTimestamp != nil {
continue
}
secretName := cert.Spec.SecretName
if secretName == "" {
continue
}
for _, dns := range cert.Spec.DNSNames {
hostname := gwapiv1.Hostname(dns)
listenerName := listenerNameFor(prefix, cert.Name, dns)
// Determine the namespace of the secret (same as cert namespace).
ns := gwapiv1.Namespace(cert.Namespace)
listeners = append(listeners, gwapiv1.Listener{
Name: gwapiv1.SectionName(listenerName),
Hostname: &hostname,
Port: defaultPort,
Protocol: gwapiv1.HTTPSProtocolType,
AllowedRoutes: &gwapiv1.AllowedRoutes{
Namespaces: &gwapiv1.RouteNamespaces{
From: &namespacesFromAll,
},
},
TLS: &gwapiv1.ListenerTLSConfig{
Mode: &tlsModeTerminate,
CertificateRefs: []gwapiv1.SecretObjectReference{
{
Group: ptrTo(gwapiv1.Group("")),
Kind: ptrTo(gwapiv1.Kind("Secret")),
Name: gwapiv1.ObjectName(secretName),
Namespace: &ns,
},
},
},
})
}
}
// Sort for deterministic output.
sort.Slice(listeners, func(i, j int) bool {
return string(listeners[i].Name) < string(listeners[j].Name)
})
return listeners
}
// MergeListeners takes existing Gateway listeners and replaces all managed
// (prefixed) listeners with the desired set, preserving user-defined listeners.
func MergeListeners(existing, desired []gwapiv1.Listener, prefix string) []gwapiv1.Listener {
var merged []gwapiv1.Listener
// Keep all non-managed listeners.
for _, l := range existing {
if !strings.HasPrefix(string(l.Name), prefix) {
merged = append(merged, l)
}
}
// Append desired managed listeners.
merged = append(merged, desired...)
return merged
}
// ListenersEqual does a quick comparison of two listener slices by name+hostname+secretRef.
// Not a deep equal — we only check the fields we manage.
func ListenersEqual(a, b []gwapiv1.Listener) bool {
if len(a) != len(b) {
return false
}
aMap := listenerMap(a)
bMap := listenerMap(b)
if len(aMap) != len(bMap) {
return false
}
for k, av := range aMap {
bv, ok := bMap[k]
if !ok || av != bv {
return false
}
}
return true
}
type listenerKey struct {
name string
hostname string
secret string
port gwapiv1.PortNumber
}
func listenerMap(listeners []gwapiv1.Listener) map[string]listenerKey {
m := make(map[string]listenerKey, len(listeners))
for _, l := range listeners {
key := listenerKey{
name: string(l.Name),
port: l.Port,
}
if l.Hostname != nil {
key.hostname = string(*l.Hostname)
}
if l.TLS != nil && len(l.TLS.CertificateRefs) > 0 {
ref := l.TLS.CertificateRefs[0]
ns := ""
if ref.Namespace != nil {
ns = string(*ref.Namespace)
}
key.secret = fmt.Sprintf("%s/%s", ns, ref.Name)
}
m[key.name] = key
}
return m
}
// listenerNameFor generates a deterministic listener name from cert name and DNS name.
// Truncates to stay within Gateway API's 253-char limit for section names.
func listenerNameFor(prefix, certName, dnsName string) string {
// Replace dots with dashes for DNS names, combine with cert name.
sanitized := strings.ReplaceAll(dnsName, ".", "-")
name := fmt.Sprintf("%s%s-%s", prefix, certName, sanitized)
if len(name) > 253 {
name = name[:253]
}
return name
}
func ptrTo[T any](v T) *T {
return &v
}