I’m trying to set up a Network Load Balancer (NLB) in AWS and associate it with multiple security groups. I’m using AWS CloudFormation with a YAML template to configure the NLB. However, I encounter an issue where the NLB does not seem to associate with more than one security group.

Example

Here is what I have tried so far:

• Created a Network Load Balancer using the AWS Management Console.
• Attempted to attach multiple security groups to the NLB.

Resources:
  MyNetworkLoadBalancer:
    Type: AWS::ElasticLoadBalancingV2::LoadBalancer
    Properties:
      Name: my-nlb
      Type: network
      Subnets:
        - subnet-0abc123456def7890
        - subnet-0abc123456def7891
      SecurityGroups:
        - sg-0abc123456def7890
        - sg-0abc123456def7891

  MyTargetGroup:
    Type: AWS::ElasticLoadBalancingV2::TargetGroup
    Properties:
      Name: my-target-group
      Port: 80
      Protocol: TCP
      VpcId: vpc-0abc123456def7890

  MyListener:
    Type: AWS::ElasticLoadBalancingV2::Listener
    Properties:
      DefaultActions:
        - Type: forward
          TargetGroupArn: !Ref MyTargetGroup
      LoadBalancerArn: !Ref MyNetworkLoadBalancer
      Port: 80
      Protocol: TCP

What I Tried:

• Verified that the subnets and security groups exist and are properly configured.
• Ensured that the VPC is correctly set up.
• Attempted to manually associate the security groups through the AWS Management Console, which works, but not through the CloudFormation template.

I expected the NLB to be created with both security groups (sg-0abc123456def7890 and sg-0abc123456def7891) associated with it as specified in the YAML file. This should allow the NLB to follow the rules defined in both security groups.