Denish Patel deployed PostgreSQL on Amazon EC2 for a startup that had its entire IT architecture on the Amazon cloud. The initial deployment involved setting up master-slave configurations across two EC2 environments with issues like weekly instance failures and lack of monitoring. Patel then consolidated the environments, configured high availability using replication across availability zones and regions, implemented automation using Puppet, and added monitoring and backups to improve the stability and management of the PostgreSQL deployment.