fix(apigateway): unable to associate RestApi as a route53 target for late bound domains

packages/@aws-cdk/aws-apigateway/lib/restapi.ts

@@ -212,13 +212,8 @@ export class RestApi extends Resource implements IRestApi {
    */
   public deploymentStage!: Stage;
 
-  /**
-   * The domain name mapped to this API, if defined through the `domainName`
-   * configuration prop.
-   */
-  public readonly domainName?: DomainName;
-
   private readonly methods = new Array<Method>();
+  private _domainName?: DomainName;
   private _latestDeployment: Deployment | undefined;
 
   constructor(scope: Construct, id: string, props: RestApiProps = { }) {
@@ -253,10 +248,18 @@ export class RestApi extends Resource implements IRestApi {
     this.restApiRootResourceId = resource.attrRootResourceId;
 
     if (props.domainName) {
-      this.domainName = this.addDomainName('CustomDomain', props.domainName);
+      this.addDomainName('CustomDomain', props.domainName);
     }
   }
 
+  /**
+   * The first domain name mapped to this API, if defined through the `domainName`
+   * configuration prop, or added via `addDomainName`
+   */
+  public get domainName() {
+    return this._domainName;
+  }
+
   /**
    * API Gateway deployment that represents the latest changes of the API.
    * This resource will be automatically updated every time the REST API model changes.
@@ -292,10 +295,14 @@ export class RestApi extends Resource implements IRestApi {
    * @param options custom domain options
    */
   public addDomainName(id: string, options: DomainNameOptions): DomainName {
-    return new DomainName(this, id, {
+    const domainName = new DomainName(this, id, {
       ...options,
       mapping: this
     });
+    if (!this._domainName) {
+      this._domainName = domainName;
+    }
+    return domainName;
   }
 
   /**

packages/@aws-cdk/aws-apigateway/test/test.domains.ts

@@ -177,6 +177,112 @@ export = {
       }
     }));
 
+    test.done();
+  },
+
+  'a domain name can be added later'(test: Test) {
+    // GIVEN
+    const domainName = 'my.domain.com';
+    const stack = new Stack();
+    const certificate = new acm.Certificate(stack, 'cert', { domainName: 'my.domain.com' });
+
+    // WHEN
+    const api = new apigw.RestApi(stack, 'api', {});
+
+    api.root.addMethod('GET');
+
+    api.addDomainName('domainId', { domainName, certificate });
+
+    // THEN
+    expect(stack).to(haveResource('AWS::ApiGateway::DomainName', {
+      "DomainName": domainName,
+      "EndpointConfiguration": {
+        "Types": [
+          "REGIONAL"
+        ]
+      },
+      "RegionalCertificateArn": {
+        "Ref": "cert56CA94EB"
+      }
+    }));
+    expect(stack).to(haveResource('AWS::ApiGateway::BasePathMapping', {
+      "DomainName": {
+        "Ref": "apidomainId102F8DAA"
+      },
+      "RestApiId": {
+        "Ref": "apiC8550315"
+      },
+      "Stage": {
+        "Ref": "apiDeploymentStageprod896C8101"
+      }
+    }));
+
+    test.done();
+  },
+
+  'multiple domain names can be added'(test: Test) {
+    // GIVEN
+    const domainName = 'my.domain.com';
+    const stack = new Stack();
+    const certificate = new acm.Certificate(stack, 'cert', { domainName: 'my.domain.com' });
+
+    // WHEN
+    const api = new apigw.RestApi(stack, 'api', {});
+
+    api.root.addMethod('GET');
+
+    const domainName1 = api.addDomainName('domainId', { domainName, certificate });
+    api.addDomainName('domainId1', { domainName: 'your.domain.com', certificate });
+    api.addDomainName('domainId2', { domainName: 'our.domain.com', certificate });
+
+    test.deepEqual(api.domainName, domainName1);
+
+    // THEN
+    expect(stack).to(haveResource('AWS::ApiGateway::DomainName', {
+      "DomainName": 'my.domain.com',
+      "EndpointConfiguration": {
+        "Types": [
+          "REGIONAL"
+        ]
+      },
+      "RegionalCertificateArn": {
+        "Ref": "cert56CA94EB"
+      }
+    }));
+    expect(stack).to(haveResource('AWS::ApiGateway::DomainName', {
+      "DomainName": 'your.domain.com',
+      "EndpointConfiguration": {
+        "Types": [
+          "REGIONAL"
+        ]
+      },
+      "RegionalCertificateArn": {
+        "Ref": "cert56CA94EB"
+      }
+    }));
+    expect(stack).to(haveResource('AWS::ApiGateway::DomainName', {
+      "DomainName": 'our.domain.com',
+      "EndpointConfiguration": {
+        "Types": [
+          "REGIONAL"
+        ]
+      },
+      "RegionalCertificateArn": {
+        "Ref": "cert56CA94EB"
+      }
+    }));
+    expect(stack).to(haveResource('AWS::ApiGateway::BasePathMapping', {
+      "DomainName": {
+        "Ref": "apidomainId102F8DAA"
+      },
+      "RestApiId": {
+        "Ref": "apiC8550315"
+      },
+      "Stage": {
+        "Ref": "apiDeploymentStageprod896C8101"
+      }
+    }));
+
     test.done();
   }
 };