AWS Cloudformation: Fn::GetAtt into Fn::ImportValue - amazon-web-services

Question

I have a stack to create an VPC.
This stack exports an output for VPC ID with name VPCID. Lools like this.
Outputs:
Output0:
Description: The ID of the VPC
Value: !Ref VPC0
Export:
Name: VPCID
I can import the output into my child stacks.
sghttps:
Type: AWS::EC2::SecurityGroup
Properties:
GroupDescription: 'HTTPS'
GroupName: https
SecurityGroupIngress:
- FromPort: 443
ToPort: 443
IpProtocol: tcp
CidrIp: '0.0.0.0/0'
Description: 'HTTPS from EVERYWHERE'
SecurityGroupEgress:
- FromPort: 0
ToPort: 0
IpProtocol: '-1'
CidrIp: '0.0.0.0/0'
VpcId: !ImportValue VPCID
Tags:
- Key: CF
Value: true
Now, I need access to the attribute CidrBlock of this VPC in my child stacks.
Somethigs like this.
sgmongodb:
Type: AWS::EC2::SecurityGroup
Properties:
GroupDescription: 'MONGODB'
GroupName: mongodb
SecurityGroupIngress:
- FromPort: 27017
ToPort: 27017
IpProtocol: tcp
CidrIp: !ImportValue VPCID.CidrBlock
Description: 'MongoDB from our VPC TCP'
or like this.
sgmongodb:
Type: AWS::EC2::SecurityGroup
Properties:
GroupDescription: 'MONGODB'
GroupName: mongodb
SecurityGroupIngress:
- FromPort: 27017
ToPort: 27017
IpProtocol: tcp
CidrIp: !ImportValue 'Fn::GetAtt':
- VPCID
- CidrBlock
Description: 'MongoDB from our VPC TCP'
I'm aware that is posible export the value of CidrBlock.
Outputs:
Output0:
Description: The ID of the VPC
Value: !Ref VPC0
Export:
Name: VPCID
Output1:
Description: CidrBlock
Value: !GetAtt VPC0.CidrBlock
Export:
Name: VPCIDCidrBlock
But, Is posible pass only the main VPS (VPCID in my case) resource and get the attribute CidrBlock in the child stack?
I do not find the rigth syntax. Any idea?

Answer 1

But, Is posible pass only the main VPS (VPCID in my case) resource and get the attribute CidrBlock in the child stack?
No its not, without a Custom Resource in your child module. Such a resource would be in the form of a lambda function which would take the VPCID as an input paramter, used AWS SDK to query the VPC for its CIDR range, and return it to your child stack for further use.
If you don't want to create a custom resource, you have to export your CIDR range as well, and any other info that you require.