Spilo is a tool that provides high availability for PostgreSQL databases running on AWS. It uses Patroni and ETCD to handle replication, failover, and cluster state management. Teams at Zalando use Spilo to run over 150 PostgreSQL databases in a self-managed way on AWS, with each team responsible for their own databases. Spilo provides automation for deploying, replicating, and failing over PostgreSQL clusters on AWS, allowing for increased agility compared to managed database services.