CloudFormation fails to find RDS Subnet Group because of lowercase - amazon-web-services

Question

I created my RDS Subnet Group via CloudFormation referencing a parameter ProjectName
DB:
Type: AWS::RDS::DBInstance
Properties:
DBSubnetGroupName: !Ref RDSSubnetGroup
Problem now is CloudFormation says it cannot find my subnet group:
DB subnet group 'AbcDef' does not exist because its actually abcdef ... how can I resolve this?
I tried looking for a toLower function but seems like theres none?
The other option appears to be recreate the stack?

Answer 1

Unfortunately everything you do in CloudFormation templates is case-sensitive including property names and parameter values. You may have to recreate the stack.
As you correctly pointed out, there is no Fn::ToLower function. If you really want to achieve what you are trying to, the only way to do it as of now is create Lambda backed custom resource which basically will convert your string to lower case and return it but it is not worth doing it as there are plenty of challenges you will come across when dealing with custom resources.

Answer 2

I have also found that DB Subnet Groups have their name forcibly changed to lowercase when viewed in the RDS console. Very unusual behavior.
However, I have created them in CloudFormation and it has not caused the error you describe. Here are the bits from my CloudFormation template:
###########
# DB Subnet Group
###########
DBSubnetGroup:
Type: AWS::RDS::DBSubnetGroup
Properties:
DBSubnetGroupDescription: Lab DB Subnet Group
DBSubnetGroupName: Lab DB Subnet Group
SubnetIds:
- !Ref PrivateSubnet1
- !Ref PrivateSubnet2
Tags:
-
Key: Name
Value: DBSubnetGroup
###########
# RDS Database
###########
RDSDatabase:
Type: AWS::RDS::DBInstance
Properties:
DBName: inventory
DBInstanceIdentifier: inventory-db
AllocatedStorage: 5
DBInstanceClass: db.t2.micro
Engine: MySQL
MasterUsername: master
MasterUserPassword: lab-password
MultiAZ: false
DBSubnetGroupName: !Ref DBSubnetGroup
VPCSecurityGroups:
- !Ref DBSecurityGroup
Tags:
-
Key: Name
Value: inventory-db

Answer 3

I would suggest rewriting the function_name and the name of the DBSubnetGroup to dbsubnetgroup
This will fix the issue I suppose.

Answer 4

Had the same issue, tried all possible , the only way to fix , was to create a new DB subnet group with the name lower :
rdssubnetgrouplower:
Type: "AWS::RDS::DBSubnetGroup"
Properties:
DBSubnetGroupDescription: "Private subnet group to keep the cluster private"
DBSubnetGroupName: rdssubnetgrouplower
SubnetIds:
- !Ref PrivateSubnet1
- !Ref PrivateSubnet2
Tags:
-
Key: Name
Value: rdssubnetgrouplower
and then in RDS definition used it :
MySQLABC:
Type: "AWS::RDS::DBCluster"
Properties:
DBSubnetGroupName: !Ref rdssubnetgrouplower
...
...
this worked and had the cluster up. in TF there is the lower function :)