[SOLVED] Do I need to create a reader and writer db instance when creating an AWS Aurora Serverless V2 cluster?

Do I need to create a reader and writer db instance when creating an AWS Aurora Serverless V2 cluster?

I'm creating an AWS Aurora Serverless V2 Postgres database cluster (AWS::RDS::DBCluster) using Cloudformation and Serverless Framework (see below). It's unclear if I should also create two database instances (AWS::RDS::DBInstance) so that the cluster has a reader and writer instance available?

When I run through the AWS RDS Wizard the Aurora Serverless V2 cluster is automatically set up with two instances (reader and writer). I'm assuming I should do the same when creating the CloudFormation script?

Cluster

Type: AWS::RDS::DBCluster
DeletionPolicy: Delete
Properties:
  DBClusterIdentifier: db-test-cluster
  Engine: aurora-postgresql
  MasterUsername: username_from_secrets_manager
  MasterUserPassword: password_from_secrets_manager
  ServerlessV2ScalingConfiguration:
    MinCapacity: 0.5
    MaxCapacity: 2
  BackupRetentionPeriod: 1
  DatabaseName: test-db
  EngineMode: provisioned
  Port: 5432
  Tags:
    - Key: "Name"
      Value: db-test-cluster

DbInstance 1 - reader

Type: AWS::RDS::DBInstance
Properties:
  Engine: aurora-postgresql
  DBInstanceClass: db.serverless
  DBClusterIdentifier: !Ref auroraServerlessCluster

DbInstance 2 - writer

Type: AWS::RDS::DBInstance
Properties:
  Engine: aurora-postgresql
  DBInstanceClass: db.serverless
  DBClusterIdentifier: !Ref auroraServerlessCluster

Do I need to specify these two db instances? When I don't specify these two instances my cluster is stick with "creating" as the status.

Solution

There's no requirement to have any read-replica instances in an Aurora cluster (serverless or not). You can create an Aurora cluster with a single primary writer instance and nothing else. You can even create a cluster with no instances if you want, although that certainly has limited functionality.