fix(opensearch): Don't throw a Az count mismatch for imported VPCs

packages/@aws-cdk/aws-opensearchservice/lib/domain.ts

@@ -1235,8 +1235,11 @@ export class Domain extends DomainBase implements IDomain, ec2.IConnectable {
     let securityGroups: ec2.ISecurityGroup[] | undefined;
     let subnets: ec2.ISubnet[] | undefined;
 
+    let skipZoneAwarenessCheck: boolean = false;
     if (props.vpc) {
-      subnets = selectSubnets(props.vpc, props.vpcSubnets ?? [{ subnetType: ec2.SubnetType.PRIVATE_WITH_EGRESS }]);
+      const subnetSelections = props.vpcSubnets ?? [{ subnetType: ec2.SubnetType.PRIVATE_WITH_EGRESS }];
+      subnets = selectSubnets(props.vpc, subnetSelections);
+      skipZoneAwarenessCheck = zoneAwarenessCheckShouldBeSkipped(props.vpc, subnetSelections);
       securityGroups = props.securityGroups ?? [new ec2.SecurityGroup(this, 'SecurityGroup', {
         vpc: props.vpc,
         description: `Security group for domain ${this.node.id}`,
@@ -1248,8 +1251,12 @@ export class Domain extends DomainBase implements IDomain, ec2.IConnectable {
       }
     }
 
-    // If VPC options are supplied ensure that the number of subnets matches the number AZ
-    if (subnets && zoneAwarenessEnabled && new Set(subnets.map((subnet) => subnet.availabilityZone)).size < availabilityZoneCount) {
+    // If VPC options are supplied ensure that the number of subnets matches the number AZ (only if the vpc is not imported from another stack)
+    if (subnets &&
+      zoneAwarenessEnabled &&
+      !skipZoneAwarenessCheck &&
+      new Set(subnets.map((subnet) => subnet.availabilityZone)).size < availabilityZoneCount
+    ) {
       throw new Error('When providing vpc options you need to provide a subnet for each AZ you are using');
     }
 
@@ -1776,6 +1783,22 @@ function selectSubnets(vpc: ec2.IVpc, vpcSubnets: ec2.SubnetSelection[]): ec2.IS
   return selected;
 }
 
+/**
+ * Check if any of the subnets are pending lookups. If so, the zone awareness check should be skipped, otherwise it will always throw an error
+ *
+ * @param vpc The vpc to which the subnets apply
+ * @param vpcSubnets The vpc subnets that should be checked
+ * @returns true if there are pending lookups for the subnets
+ */
+function zoneAwarenessCheckShouldBeSkipped(vpc: ec2.IVpc, vpcSubnets: ec2.SubnetSelection[]): boolean {
+  for (const selection of vpcSubnets) {
+    if (vpc.selectSubnets(selection).isPendingLookup) {
+      return true;
+    };
+  }
+  return false;
+}
+
 /**
  * Initializes an instance type.
  *

packages/@aws-cdk/aws-opensearchservice/test/domain.test.ts

@@ -2,7 +2,7 @@
 import { Match, Template } from '@aws-cdk/assertions';
 import * as acm from '@aws-cdk/aws-certificatemanager';
 import { Metric, Statistic } from '@aws-cdk/aws-cloudwatch';
-import { Vpc, EbsDeviceVolumeType, Port, SecurityGroup } from '@aws-cdk/aws-ec2';
+import { Vpc, EbsDeviceVolumeType, Port, SecurityGroup, SubnetType } from '@aws-cdk/aws-ec2';
 import * as iam from '@aws-cdk/aws-iam';
 import * as kms from '@aws-cdk/aws-kms';
 import * as logs from '@aws-cdk/aws-logs';
@@ -1406,6 +1406,27 @@ describe('custom error responses', () => {
     })).toThrow(/you need to provide a subnet for each AZ you are using/);
   });
 
+  test('Imported VPC with subnets that are still pending lookup won\'t throw Az count mismatch', () => {
+    const vpc = Vpc.fromLookup(stack, 'ExampleVpc', {
+      vpcId: 'vpc-123',
+    });
+    let subnets = vpc.selectSubnets({
+      subnetType: SubnetType.PRIVATE_WITH_EGRESS,
+    });
+
+    new Domain(stack, 'Domain1', {
+      version: defaultVersion,
+      vpc,
+      vpcSubnets: [subnets],
+      zoneAwareness: {
+        enabled: true,
+        availabilityZoneCount: 3,
+      },
+    });
+
+    Template.fromStack(stack).resourceCountIs('AWS::OpenSearchService::Domain', 1);
+  });
+
   test('error when master, data or Ultra Warm instance types do not end with .search', () => {
     const error = /instance types must end with ".search"/;
     expect(() => new Domain(stack, 'Domain1', {

packages/@aws-cdk/aws-opensearchservice/test/integ.opensearch.imported-vpc.js.snapshot/StackWithVpc.assets.json

@@ -0,0 +1,20 @@
+{
+  "version": "21.0.0",
+  "files": {
+    "b723f0bed9ea9a4e8d237408e0debfa443e0a646b76eeeab26215935a74297bf": {
+      "source": {
+        "path": "StackWithVpc.template.json",
+        "packaging": "file"
+      },
+      "destinations": {
+        "12345678-test-region": {
+          "bucketName": "cdk-hnb659fds-assets-12345678-test-region",
+          "objectKey": "b723f0bed9ea9a4e8d237408e0debfa443e0a646b76eeeab26215935a74297bf.json",
+          "region": "test-region",
+          "assumeRoleArn": "arn:${AWS::Partition}:iam::12345678:role/cdk-hnb659fds-file-publishing-role-12345678-test-region"
+        }
+      }
+    }
+  },
+  "dockerImages": {}
+}