Add IPv6 support to PrefectServer

api/v1/prefectserver_types.go

@@ -36,6 +36,13 @@ type PrefectServerSpec struct {
 	// Image defines the exact image to deploy for the Prefect Server, overriding Version
 	Image *string `json:"image,omitempty"`
 
+	// Host defines the host address to bind the Prefect Server to.
+	// Defaults to "0.0.0.0" for IPv4 compatibility.
+	// Use "" (empty string) to bind to all interfaces for IPv6-only or dual-stack environments.
+	// Note: Prefect does not accept "::" as a valid host value.
+	// +kubebuilder:validation:Optional
+	Host *string `json:"host,omitempty"`
+
 	// Resources defines the CPU and memory resources for each replica of the Prefect Server
 	Resources corev1.ResourceRequirements `json:"resources,omitempty"`
 
@@ -394,8 +401,13 @@ func (s *PrefectServer) Image() string {
 	return DEFAULT_PREFECT_IMAGE
 }
 
-func (s *PrefectServer) EntrypointArugments() []string {
-	command := []string{"prefect", "server", "start", "--host", "0.0.0.0"}
+func (s *PrefectServer) EntrypointArguments() []string {
+	host := "0.0.0.0" // Default to IPv4 for backward compatibility
+	if s.Spec.Host != nil {
+		host = *s.Spec.Host
+	}
+
+	command := []string{"prefect", "server", "start", "--host", host}
 	command = append(command, s.Spec.ExtraArgs...)
 
 	return command

api/v1/prefectserver_types_test.go

@@ -620,5 +620,50 @@ var _ = Describe("PrefectServer type", func() {
 
 			Expect(envVars).To(ConsistOf(expectedEnvVars))
 		})
+
+		Context("Host binding configuration", func() {
+			It("should use default host 0.0.0.0 when Host is nil", func() {
+				server := &PrefectServer{
+					Spec: PrefectServerSpec{},
+				}
+
+				args := server.EntrypointArguments()
+				Expect(args).To(Equal([]string{"prefect", "server", "start", "--host", "0.0.0.0"}))
+			})
+
+			It("should use empty string for IPv6/dual-stack when specified", func() {
+				server := &PrefectServer{
+					Spec: PrefectServerSpec{
+						Host: ptr.To(""),
+					},
+				}
+
+				args := server.EntrypointArguments()
+				Expect(args).To(Equal([]string{"prefect", "server", "start", "--host", ""}))
+			})
+
+			It("should use custom host with ExtraArgs", func() {
+				server := &PrefectServer{
+					Spec: PrefectServerSpec{
+						Host:      ptr.To(""),
+						ExtraArgs: []string{"--some-arg", "some-value"},
+					},
+				}
+
+				args := server.EntrypointArguments()
+				Expect(args).To(Equal([]string{"prefect", "server", "start", "--host", "", "--some-arg", "some-value"}))
+			})
+
+			It("should use specific IPv4 address when specified", func() {
+				server := &PrefectServer{
+					Spec: PrefectServerSpec{
+						Host: ptr.To("127.0.0.1"),
+					},
+				}
+
+				args := server.EntrypointArguments()
+				Expect(args).To(Equal([]string{"prefect", "server", "start", "--host", "127.0.0.1"}))
+			})
+		})
 	})
 })

deploy/charts/prefect-operator/crds/prefect.io_prefectservers.yaml

@@ -1661,6 +1661,13 @@ spec:
                   - port
                   type: object
                 type: array
+              host:
+                description: |-
+                  Host defines the host address to bind the Prefect Server to.
+                  Defaults to "0.0.0.0" for IPv4 compatibility.
+                  Use "" (empty string) to bind to all interfaces for IPv6-only or dual-stack environments.
+                  Note: Prefect does not accept "::" as a valid host value.
+                type: string
               image:
                 description: Image defines the exact image to deploy for the Prefect
                   Server, overriding Version

deploy/samples/v1_prefectserver_dualstack.yaml

@@ -0,0 +1,13 @@
+---
+apiVersion: prefect.io/v1
+kind: PrefectServer
+metadata:
+  name: prefect-dualstack
+  labels:
+    app.kubernetes.io/name: prefect-operator
+    app.kubernetes.io/managed-by: kustomize
+spec:
+  host: "" # Empty string for dual-stack (uvicorn binds to all interfaces)
+  sqlite:
+    storageClassName: local-path
+    size: 1Gi

deploy/samples/v1_prefectserver_ipv6.yaml

@@ -0,0 +1,10 @@
+apiVersion: prefect.io/v1
+kind: PrefectServer
+metadata:
+  name: prefect-ipv6
+  labels:
+    app.kubernetes.io/name: prefect-operator
+    app.kubernetes.io/managed-by: kustomize
+spec:
+  host: ""  # Empty string binds to all interfaces (works for IPv6-only and dual-stack)
+  ephemeral: {}

internal/controller/prefectserver_controller.go

@@ -374,7 +374,7 @@ func (r *PrefectServerReconciler) ephemeralDeploymentSpec(server *prefectiov1.Pr
 						Image:           server.Image(),
 						ImagePullPolicy: corev1.PullIfNotPresent,
 
-						Args: server.EntrypointArugments(),
+						Args: server.EntrypointArguments(),
 						VolumeMounts: []corev1.VolumeMount{
 							{
 								Name:      "prefect-data",
@@ -458,7 +458,7 @@ func (r *PrefectServerReconciler) sqliteDeploymentSpec(server *prefectiov1.Prefe
 						Image:           server.Image(),
 						ImagePullPolicy: corev1.PullIfNotPresent,
 
-						Args: server.EntrypointArugments(),
+						Args: server.EntrypointArguments(),
 						VolumeMounts: []corev1.VolumeMount{
 							{
 								Name:      "prefect-data",
@@ -514,7 +514,7 @@ func (r *PrefectServerReconciler) postgresDeploymentSpec(server *prefectiov1.Pre
 						Image:           server.Image(),
 						ImagePullPolicy: corev1.PullIfNotPresent,
 
-						Args: server.EntrypointArugments(),
+						Args: server.EntrypointArguments(),
 						Env:  server.ToEnvVars(),
 						Ports: []corev1.ContainerPort{
 							{

internal/controller/prefectserver_controller_test.go

@@ -644,6 +644,41 @@ var _ = Describe("PrefectServer controller", func() {
 				Expect(container.Command).To(BeNil())
 				Expect(container.Args).To(Equal([]string{"prefect", "server", "start", "--host", "0.0.0.0", "--some-arg", "some-value"}))
 			})
+
+			It("should create a Deployment with IPv6/dual-stack host (empty string)", func() {
+				name := types.NamespacedName{
+					Namespace: namespaceName,
+					Name:      "prefect-ipv6-server",
+				}
+
+				prefectserver := &prefectiov1.PrefectServer{
+					ObjectMeta: metav1.ObjectMeta{
+						Namespace: namespaceName,
+						Name:      "prefect-ipv6-server",
+					},
+					Spec: prefectiov1.PrefectServerSpec{
+						Host: ptr.To(""),
+					},
+				}
+				Expect(k8sClient.Create(ctx, prefectserver)).To(Succeed())
+
+				controllerReconciler := &PrefectServerReconciler{
+					Client: k8sClient,
+					Scheme: k8sClient.Scheme(),
+				}
+				_, err := controllerReconciler.Reconcile(ctx, reconcile.Request{
+					NamespacedName: name,
+				})
+				Expect(err).NotTo(HaveOccurred())
+
+				deployment := &appsv1.Deployment{}
+				Eventually(func() error {
+					return k8sClient.Get(ctx, name, deployment)
+				}).Should(Succeed())
+
+				container := deployment.Spec.Template.Spec.Containers[0]
+				Expect(container.Args).To(Equal([]string{"prefect", "server", "start", "--host", ""}))
+			})
 		})
 
 		Context("When evaluating changes with any server", func() {