Security Group referencing in cloudformation is not working

Question

I have 2 templates

1. For security group.
Resources:
  MyInstanceSecurityGroup:
    Type: 'AWS::EC2::SecurityGroup'
    Properties:
      GroupDescription: Enable SSH access to the instance
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: '22'
          ToPort: '22'
          CidrIp: '0.0.0.0/0'
Outputs:
  MyInstanceSecurityGroup:
    Description: security GroupId
    Value: 
      !GetAtt
        - MyInstanceSecurityGroup
        - GroupId
    Export:
      Name:  !Sub "${AWS::StackName}-SecurityGroupID"

2. Creating a web server using the security group in 1st stack
---
Parameters:
  Key:
    Description: Enter the name of the existing key pair
    Type: 'AWS::EC2::KeyPair::KeyName'
    ConstraintDescription: must be the name of an existing EC2 KeyPair.
  InstanceType:
    Description: WebServer EC2 instance type
    Type: String
    Default: t2.small
    AllowedValues:
      - t1.micro
      - t2.nano
      - t2.micro
      - t2.small
    ConstraintDescription: must be a valid EC2 instance type.
Resources:
  MyElasticIP: 
    Type: AWS::EC2::EIP
    Properties: 
      InstanceId: !Ref MyInstance
  MyInstance:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: ami-026b57f3c383c2eec
      AvailabilityZone: us-east-1a
      InstanceType: !Ref InstanceType
      KeyName: !Ref Key
      SecurityGroups: Fn::ImportValue
        !Sub "${sg-new}-MyInstanceSecurityGroup"
But I am getting an error while creating a second stack as
"Value of property SecurityGroups must be of type List of String"
Could you help me resolve this?

kentrad · Answer

You export with a name like this;

```
Name: !Sub "${AWS::StackName}-SecurityGroupID"
```
But you import it with name like this:

```
Fn::ImportValue !Sub "${sg-new}-MyInstanceSecurityGroup
```

I'm not sure where `${sg-new}` comes from, but the last part should match the name you exported, `-SecurityGroupID`, not the logical name from the first template.

Security Group referencing in cloudformation is not working

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