fix(eks): private endpoint access doesn't work with Vpc.fromLookup

packages/@aws-cdk/aws-eks/lib/cluster.ts

@@ -1018,13 +1018,20 @@ export class Cluster extends Resource implements ICluster {
       };
 
       if (!this.endpointAccess._config.publicAccess) {
+
+        const privateSubents = this.selectPrivateSubnets().slice(0, 16);
+
+        if (privateSubents.length === 0) {
+          throw new Error('Vpc must contain private subnets to configure private endpoint access');
+        }
+
         // endpoint access is private only, we need to attach the
         // provider to the VPC so that it can access the cluster.
         providerProps = {
           ...providerProps,
           vpc: this.vpc,
           // lambda can only be accociated with max 16 subnets and they all need to be private.
-          vpcSubnets: {subnets: this.selectPrivateSubnets().slice(0, 16)},
+          vpcSubnets: {subnets: privateSubents},
           securityGroups: [this.kubctlProviderSecurityGroup],
         };
       }
@@ -1049,7 +1056,26 @@ export class Cluster extends Resource implements ICluster {
     const privateSubnets: ec2.ISubnet[] = [];
 
     for (const placement of this.vpcSubnets) {
-      privateSubnets.push(...this.vpc.selectSubnets(placement).subnets.filter(s => s instanceof ec2.PrivateSubnet));
+
+      for (const subnet of this.vpc.selectSubnets(placement).subnets) {
+
+        if (this.vpc.privateSubnets.includes(subnet)) {
+          // definitely private, take it.
+          privateSubnets.push(subnet);
+          continue;
+        }
+
+        if (this.vpc.publicSubnets.includes(subnet)) {
+          // definitely public, skip it.
+          continue;
+        }
+
+        // neither public and nor private - what is it then? this means its a subnet instance that was explicitly passed
+        // in the subnet selection. since ISubnet doesn't contain information on type, we have to assume its private and let it
+        // fail at deploy time :\ (its better than filtering it out and preventing a possibly successful deployment)
+        privateSubnets.push(subnet);
+      }
+
     }
 
     return privateSubnets;

packages/@aws-cdk/aws-eks/test/test.cluster.ts

@@ -1400,6 +1400,105 @@ export = {
 
   'endpoint access': {
 
+    'private endpoint access fails if selected subnets are empty'(test: Test) {
+
+      const { stack } = testFixture();
+
+      test.throws(() => {
+        new eks.Cluster(stack, 'Cluster', {
+          vpc: new ec2.Vpc(stack, 'Vpc'),
+          version: CLUSTER_VERSION,
+          endpointAccess: eks.EndpointAccess.PRIVATE,
+          vpcSubnets: [{ subnetType: ec2.SubnetType.PUBLIC }],
+        });
+      }, /Vpc must contain private subnets to configure private endpoint access/);
+
+      test.done();
+    },
+
+    'private endpoint access selects only private subnets from looked up vpc'(test: Test) {
+
+      const vpcId = 'vpc-12345';
+      // can't use the regular fixture because it also adds a VPC to the stack, which prevents
+      // us from setting context.
+      const stack = new cdk.Stack(new cdk.App(), 'Stack', {
+        env: {
+          account: '11112222',
+          region: 'us-east-1',
+        },
+      });
+      stack.node.setContext(`vpc-provider:account=${stack.account}:filter.vpc-id=${vpcId}:region=${stack.region}:returnAsymmetricSubnets=true`, {
+        vpcId: vpcId,
+        vpcCidrBlock: '10.0.0.0/16',
+        subnetGroups: [
+          {
+            name: 'Private',
+            type: 'Private',
+            subnets: [
+              {
+                subnetId: 'subnet-private-in-us-east-1a',
+                cidr: '10.0.1.0/24',
+                availabilityZone: 'us-east-1a',
+                routeTableId: 'rtb-06068e4c4049921ef',
+              },
+            ],
+          },
+          {
+            name: 'Public',
+            type: 'Public',
+            subnets: [
+              {
+                subnetId: 'subnet-public-in-us-east-1c',
+                cidr: '10.0.0.0/24',
+                availabilityZone: 'us-east-1c',
+                routeTableId: 'rtb-0ff08e62195198dbb',
+              },
+            ],
+          },
+        ],
+      });
+      const vpc = ec2.Vpc.fromLookup(stack, 'Vpc', {
+        vpcId: vpcId,
+      });
+
+      new eks.Cluster(stack, 'Cluster', {
+        vpc,
+        version: CLUSTER_VERSION,
+        endpointAccess: eks.EndpointAccess.PRIVATE,
+      });
+
+      const nested = stack.node.tryFindChild('@aws-cdk/aws-eks.KubectlProvider') as cdk.NestedStack;
+      const template = expect(nested).value;
+
+      test.deepEqual(template.Resources.Handler886CB40B.Properties.VpcConfig.SubnetIds, [
+        'subnet-private-in-us-east-1a',
+      ]);
+
+      test.done();
+    },
+
+    'private endpoint access considers specific subnet selection'(test: Test) {
+      const { stack } = testFixture();
+      new eks.Cluster(stack, 'Cluster', {
+        version: CLUSTER_VERSION, endpointAccess:
+        eks.EndpointAccess.PRIVATE,
+        vpcSubnets: [{subnets: [ec2.PrivateSubnet.fromSubnetAttributes(stack, 'Private1', {
+          subnetId: 'subnet1',
+          availabilityZone: 'us-east-1a',
+        })]}],
+      });
+
+      const nested = stack.node.tryFindChild('@aws-cdk/aws-eks.KubectlProvider') as cdk.NestedStack;
+      const template = expect(nested).value;
+
+      test.deepEqual(template.Resources.Handler886CB40B.Properties.VpcConfig.SubnetIds, [
+        'subnet1',
+      ]);
+
+      test.done();
+
+    },
+
     'can configure private endpoint access'(test: Test) {
       // GIVEN
       const { stack } = testFixture();
@@ -1669,4 +1768,4 @@ export = {
     },
 
   },
-};
+};