use imageId prop if passed in but default to creating parameter

src/constructs/autoscaling/asg.test.ts

@@ -21,7 +21,7 @@ describe("The GuAutoScalingGroup", () => {
     userData: "user data",
   };
 
-  test("adds the AMI parameter", () => {
+  test("adds the AMI parameter if no imageId prop provided", () => {
     const stack = simpleGuStackForTesting();
 
     new GuAutoScalingGroup(stack, "AutoscalingGroup", { ...defaultProps, osType: 1 });
@@ -40,6 +40,20 @@ describe("The GuAutoScalingGroup", () => {
     });
   });
 
+  test("does not add the AMI parameter if an imageId prop provided", () => {
+    const stack = simpleGuStackForTesting();
+
+    new GuAutoScalingGroup(stack, "AutoscalingGroup", { ...defaultProps, osType: 1, imageId: "123" });
+
+    const json = SynthUtils.toCloudFormation(stack) as SynthedStack;
+
+    expect(Object.keys(json.Parameters)).not.toContain("AMI");
+
+    expect(stack).toHaveResource("AWS::AutoScaling::LaunchConfiguration", {
+      ImageId: "123",
+    });
+  });
+
   test("adds the instanceType parameter if none provided", () => {
     const stack = simpleGuStackForTesting();
 

src/constructs/autoscaling/asg.ts

@@ -12,6 +12,7 @@ import { GuAmiParameter, GuInstanceTypeParameter } from "../core";
 export interface GuAutoScalingGroupProps
   extends Omit<AutoScalingGroupProps, "imageId" | "osType" | "machineImage" | "instanceType" | "userData"> {
   instanceType?: InstanceType;
+  imageId?: string;
   osType?: OperatingSystemType;
   machineImage?: MachineImage;
   userData: string;
@@ -22,18 +23,18 @@ export interface GuAutoScalingGroupProps
 
 export class GuAutoScalingGroup extends AutoScalingGroup {
   constructor(scope: GuStack, id: string, props: GuAutoScalingGroupProps) {
-    const imageId = new GuAmiParameter(scope, "AMI", {
-      description: "AMI ID",
-    });
-
     // We need to override getImage() so that we can pass in the AMI as a parameter
     // Otherwise, MachineImage.lookup({ name: 'some str' }) would work as long
     // as the name is hard-coded
     function getImage(): MachineImageConfig {
       return {
         osType: props.osType ?? OperatingSystemType.LINUX,
         userData: UserData.custom(props.userData),
-        imageId: imageId.valueAsString,
+        imageId:
+          props.imageId ??
+          new GuAmiParameter(scope, "AMI", {
+            description: "AMI ID",
+          }).valueAsString,
       };
     }