eigw: use cluster tag key to list managed egress-only internet gateway

The API for DescribeEgressOnlyInternetGateways does not support
attachment.vpc-id filter. Thus, the call will return all available
eigw. Consequences:
- CAPA incorrectly selects an unintended eigw for use. Leading to route
  creation failure since the eigw belongs to a different VPC.
- CAPA incorrectly destroys all eigw of all VPCs. This is very
  catastrophic as it can break other workloads.

This commit changes the filter to use cluster tag instead. Additional
safeguard is also included to check if the eigw is truly attached the
VPC.

Author: tthvo

pkg/cloud/services/network/egress_only_gateways.go

@@ -136,21 +136,35 @@ func (s *Service) createEgressOnlyInternetGateway() (*types.EgressOnlyInternetGa
 }
 
 func (s *Service) describeEgressOnlyVpcInternetGateways() ([]types.EgressOnlyInternetGateway, error) {
+	// The API for DescribeEgressOnlyInternetGateways does not support filtering by VPC ID attachment.
+	// More details: https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_DescribeEgressOnlyInternetGateways.html
+	// Since the eigw is managed by CAPA, we can filter by the kubernetes cluster tag.
 	out, err := s.EC2Client.DescribeEgressOnlyInternetGateways(context.TODO(), &ec2.DescribeEgressOnlyInternetGatewaysInput{
 		Filters: []types.Filter{
-			filter.EC2.VPCAttachment(s.scope.VPC().ID),
+			filter.EC2.Cluster(s.scope.Name()),
 		},
 	})
 	if err != nil {
 		record.Eventf(s.scope.InfraCluster(), "FailedDescribeEgressOnlyInternetGateway", "Failed to describe egress only internet gateway in vpc %q: %v", s.scope.VPC().ID, err)
 		return nil, errors.Wrapf(err, "failed to describe egress only internet gateways in vpc %q", s.scope.VPC().ID)
 	}
 
-	if len(out.EgressOnlyInternetGateways) == 0 {
+	// For safeguarding, we collect only egress-only internet gateways
+	// that are attached to the VPC.
+	eigws := make([]types.EgressOnlyInternetGateway, 0)
+	for _, eigw := range out.EgressOnlyInternetGateways {
+		for _, attachment := range eigw.Attachments {
+			if aws.StringValue(attachment.VpcId) == s.scope.VPC().ID {
+				eigws = append(eigws, eigw)
+			}
+		}
+	}
+
+	if len(eigws) == 0 {
 		return nil, awserrors.NewNotFound(fmt.Sprintf("no egress only internet gateways found in vpc %q", s.scope.VPC().ID))
 	}
 
-	return out.EgressOnlyInternetGateways, nil
+	return eigws, nil
 }
 
 func (s *Service) getEgressOnlyGatewayTagParams(id string) infrav1.BuildParams {

pkg/cloud/services/network/egress_only_gateways_test.go

@@ -199,8 +199,8 @@ func TestDeleteEgressOnlyInternetGateways(t *testing.T) {
 				m.DescribeEgressOnlyInternetGateways(context.TODO(), gomock.Eq(&ec2.DescribeEgressOnlyInternetGatewaysInput{
 					Filters: []types.Filter{
 						{
-							Name:   aws.String("attachment.vpc-id"),
-							Values: []string{"vpc-gateways"},
+							Name:   aws.String("tag-key"),
+							Values: []string{infrav1.ClusterTagKey("test-cluster")},
 						},
 					},
 				})).Return(&ec2.DescribeEgressOnlyInternetGatewaysOutput{}, nil)