AWS CloudFormation RDS Instance fails to create - cannot find DBCluster - amazon-web-services

Question

I am playing around with cloudformation and running into an issue with DBSubnetGroup that I cannot get around. My goal is to build a simple setup:
a VPC with two subnets
an RDS database subnet group on those subnets
an RDS database cluster in that db subnet
a single RDS instance in that cluster
In cloudformation, I keep getting an error:
Could not find DB Cluster: MyRDSClusterId (Service: AmazonRDS; Status Code:
404; Error Code: DBClusterNotFoundFault; Request ID: ...)
Everything looks right to me, and cloudformation says my DBCluster was created correctly. What am I doing wrong here? Any insights into what I've done wrong would be greatly appreciated.
Here is my cloudformation template:
AWSTemplateFormatVersion: "2010-09-09"
Description: Stack with DBSubnetGroup, DBCluster, and one DBInstance
Resources:
MyAppVPC:
Type: AWS::EC2::VPC
Properties:
CidrBlock: 192.168.0.0/16
EnableDnsSupport: true
EnableDnsHostnames: true
InstanceTenancy: default
MyAppRDSSubnetA:
Type: AWS::EC2::Subnet
Properties:
AvailabilityZone: us-east-1a
VpcId: !Ref MyAppVPC
CidrBlock: 192.168.0.0/24
MapPublicIpOnLaunch: true
MyAppRDSSubnetB:
Type: AWS::EC2::Subnet
Properties:
AvailabilityZone: us-east-1b
VpcId: !Ref MyAppVPC
CidrBlock: 192.168.1.0/24
MapPublicIpOnLaunch: true
MyDBSubnetGroup:
Type: AWS::RDS::DBSubnetGroup
Properties:
DBSubnetGroupDescription: My App DBSubnetGroup for RDS
SubnetIds:
- !Ref MyAppRDSSubnetA
- !Ref MyAppRDSSubnetB
MyRDSCluster:
Type: AWS::RDS::DBCluster
Properties:
BackupRetentionPeriod: 1
DatabaseName: MyDB
DBClusterIdentifier: MyRDSClusterId
DBSubnetGroupName: !Ref MyDBSubnetGroup
Engine: aurora
MasterUsername: exampleUsername
MasterUserPassword: examplePassword
MyRDSInstance:
Type: AWS::RDS::DBInstance
Properties:
DBClusterIdentifier: !Ref MyRDSCluster
DBInstanceClass: db.t2.small
DBSubnetGroupName: !Ref MyDBSubnetGroup
Engine: aurora

Answer 1

Some charcter in your DBClusterIdentifier name is in uppercase.
What cloudformation does is, it automatically convert all uppercase character to lowercase.
Now when you try to attach DBInstances under the DBCluster it is not able to find with the DBClusterIdentifier you have mentioned as it contains some uppercase.
MyRDSCluster:
Type: AWS::RDS::DBCluster
Properties:
BackupRetentionPeriod: 1
DatabaseName: MyDB
DBClusterIdentifier: MyRDSClusterId <- here it converts all string to lowercase
DBSubnetGroupName: !Ref MyDBSubnetGroup
Engine: aurora
MasterUsername: exampleUsername
MasterUserPassword: examplePassword
MyRDSInstance:
Type: AWS::RDS::DBInstance
Properties:
DBClusterIdentifier: !Ref MyRDSCluster <- here it does not, so mismatch in name
DBInstanceClass: db.t2.small
DBSubnetGroupName: !Ref MyDBSubnetGroup
Engine: aurora
Solution is : give DBClusterIdentifier all in lowercase.
I hope you got your Answer :)

Answer 2

I removed the "DBClusterIdentifier" property from my cluster definition and suddenly everything worked. Hope this helps someone else one day.
Now it looks like:
MyRDSCluster:
Type: AWS::RDS::DBCluster
Properties:
BackupRetentionPeriod: 1
DatabaseName: My
DBSubnetGroupName: !Ref MyDBSubnetGroup
Engine: aurora
MasterUsername: exampleUsername
MasterUserPassword: examplePassword
Hope this helps someone else one day.
I have to say, I'm not sure I totally understand why this fixed the issue, and an explanation would be helpful (i have been searching for a while with no luck). Why can't I specify my own DBClusterIdentifier in this template?