A modern GraphQL API layer requires both horizontal scalability and high availability to support cloud native applications, which can be achieved by deploying a database such as YugabyteDB across multiple availability zones and utilizing cloud native services like Hasura Cloud. YugabyteDB provides a PostgreSQL-compliant database with built-in Raft consensus protocol for achieving high availability, while Hasura Cloud offers automatic scaling and infrastructure management for horizontal scalability. By connecting these two components, developers can create a scalable and resilient GraphQL API layer that can withstand zone-level outages and scale horizontally to meet the demands of their applications.