add configurable init container image (PR 1007 from kagent) (#92)

fixes #91 (code from
https://github.com/kagent-dev/kagent/pull/1007/files)

Signed-off-by: Peter Jausovec <peter.jausovec@solo.io>

Author: peterj

api/v1alpha1/mcpserver_types.go

@@ -231,6 +231,25 @@ type MCPServerDeployment struct {
 	// This allows for custom volume configurations beyond just secrets and configmaps.
 	// +optional
 	Volumes []corev1.Volume `json:"volumes,omitempty"`
+
+	// InitContainer defines the configuration for the init container that copies
+	// the transport adapter binary. This is used for stdio transport type.
+	// +optional
+	InitContainer *InitContainerConfig `json:"initContainer,omitempty"`
+}
+
+// InitContainerConfig defines the configuration for the init container.
+type InitContainerConfig struct {
+	// Image defines the full image reference for the init container.
+	// If specified, this overrides the default transport adapter image.
+	// Example: "myregistry.com/agentgateway/agentgateway:0.9.0-musl"
+	// +optional
+	Image string `json:"image,omitempty"`
+
+	// ImagePullPolicy defines the pull policy for the init container image.
+	// +optional
+	// +kubebuilder:validation:Enum=Always;Never;IfNotPresent
+	ImagePullPolicy corev1.PullPolicy `json:"imagePullPolicy,omitempty"`
 }
 
 // +kubebuilder:object:root=true

api/v1alpha1/zz_generated.deepcopy.go

@@ -92,6 +92,26 @@ spec:
                     description: Image defines the container image to to deploy the
                       MCP server.
                     type: string
+                  initContainer:
+                    description: |-
+                      InitContainer defines the configuration for the init container that copies
+                      the transport adapter binary. This is used for stdio transport type.
+                    properties:
+                      image:
+                        description: |-
+                          Image defines the full image reference for the init container.
+                          If specified, this overrides the default transport adapter image.
+                          Example: "myregistry.com/agentgateway/agentgateway:0.9.0-musl"
+                        type: string
+                      imagePullPolicy:
+                        description: ImagePullPolicy defines the pull policy for the
+                          init container image.
+                        enum:
+                        - Always
+                        - Never
+                        - IfNotPresent
+                        type: string
+                    type: object
                   port:
                     default: 3000
                     description: Port defines the port on which the MCP server will

config/crd/bases/kagent.dev_mcpservers.yaml

@@ -6,6 +6,7 @@ import (
 	"encoding/hex"
 	"fmt"
 	"os"
+	"regexp"
 	"sort"
 
 	"go.uber.org/multierr"
@@ -23,9 +24,14 @@ import (
 )
 
 const (
-	defaultTransportAdapterContainerImage = "ghcr.io/agentgateway/agentgateway:0.9.0-musl"
+	transportAdapterRepository     = "ghcr.io/agentgateway/agentgateway"
+	defaultTransportAdapterVersion = "0.9.0"
 )
 
+// versionRegex validates that version strings contain only allowed characters
+// (alphanumeric, dots, hyphens) to prevent potential image injection attacks
+var versionRegex = regexp.MustCompile(`^[a-zA-Z0-9.\-]+$`)
+
 // Translator is the interface for translating MCPServer objects to TransportAdapter objects.
 type Translator interface {
 	TranslateTransportAdapterOutputs(
@@ -103,10 +109,19 @@ func (t *transportAdapterTranslator) translateTransportAdapterDeployment(
 	// Create volume mounts from the MCPServer spec
 	volumeMounts := t.createVolumeMounts(server.Spec.Deployment)
 
-	transportAdapterContainerImage := defaultTransportAdapterContainerImage
-	transportAdapterVersion := os.Getenv("TRANSPORT_ADAPTER_VERSION")
-	if transportAdapterVersion != "" {
-		transportAdapterContainerImage = fmt.Sprintf("ghcr.io/agentgateway/agentgateway:%s-musl", transportAdapterVersion)
+	// Determine the init container image and pull policy to use
+	// Start with the default transport adapter image
+	transportAdapterContainerImage := getTransportAdapterImage()
+
+	initContainerPullPolicy := corev1.PullIfNotPresent
+
+	// Override with custom image if specified in the MCPServer spec
+	if server.Spec.Deployment.InitContainer != nil && server.Spec.Deployment.InitContainer.Image != "" {
+		transportAdapterContainerImage = server.Spec.Deployment.InitContainer.Image
+		initContainerPullPolicy = server.Spec.Deployment.InitContainer.ImagePullPolicy
+		if initContainerPullPolicy == "" {
+			initContainerPullPolicy = corev1.PullIfNotPresent
+		}
 	}
 
 	var template corev1.PodSpec
@@ -118,7 +133,7 @@ func (t *transportAdapterTranslator) translateTransportAdapterDeployment(
 			InitContainers: []corev1.Container{{
 				Name:            "copy-binary",
 				Image:           transportAdapterContainerImage,
-				ImagePullPolicy: corev1.PullIfNotPresent,
+				ImagePullPolicy: initContainerPullPolicy,
 				Command:         []string{},
 				Args: []string{
 					"--copy-self",
@@ -544,3 +559,28 @@ func (t *transportAdapterTranslator) runPlugins(
 
 	return objects, errs
 }
+
+// validateVersion validates that a version string contains only allowed characters
+// to prevent potential image injection attacks
+func validateVersion(version string) error {
+	if !versionRegex.MatchString(version) {
+		return fmt.Errorf("invalid version format: %s (only alphanumeric characters, dots, and hyphens are allowed)", version)
+	}
+	return nil
+}
+
+// getTransportAdapterImage returns the transport adapter container image,
+// using the environment variable if provided and valid, otherwise using the default
+func getTransportAdapterImage() string {
+	transportAdapterVersion := os.Getenv("TRANSPORT_ADAPTER_VERSION")
+	if transportAdapterVersion == "" {
+		return fmt.Sprintf("%s:%s-musl", transportAdapterRepository, defaultTransportAdapterVersion)
+	}
+
+	if err := validateVersion(transportAdapterVersion); err != nil {
+		klog.Warningf("Invalid TRANSPORT_ADAPTER_VERSION: %v, fallback to %s", err, defaultTransportAdapterVersion)
+		return fmt.Sprintf("%s:%s-musl", transportAdapterRepository, defaultTransportAdapterVersion)
+	}
+
+	return fmt.Sprintf("%s:%s-musl", transportAdapterRepository, transportAdapterVersion)
+}