Amazon can host your postgres database in their RDS service. We recommend using AWS RDS or GCP Cloud SQL to productionalize your security_monkey deployment.
Create a Postgres RDS instance in the same region you intend to launch your security_monkey instance.
The AWS supplied defaults should get you going. You will need to use the hostname, dbname, username, password to create a SQLALCHEMY_DATABASE_URI for your config.
SQLALCHEMY_DATABASE_URI = 'postgresql://securitymonkeyuser:securitymonkeypassword@hostname:5432/secmonkey'
Advanced users may wish to supply a KMS key for encryption at rest.