Isolated application environments, as explored in a blog post by Dian M Fay, offer a tailored approach to database-per-user architecture by providing separate systems for each customer, as opposed to a shared environment. This method addresses specific needs such as compliance with data residency laws, allowing customers to dictate upgrade schedules, and accommodating geographical preferences. However, it requires significant operational overhead, as each customer's system must be uniquely managed, provisioned, and maintained, often involving complex version management and a central control plane. Although this setup can enhance flexibility and cater to individual customer demands, it also introduces challenges in maintaining uniformity across deployments. The article underscores that while isolated environments offer distinct benefits, they demand careful consideration and substantial resources, making them suitable only under certain conditions. This piece is part of a series examining database-per-user architectures, with previous parts focusing on multi-tenancy, control planes, and shared application environments.