Oliver Koo, a Senior Mobile Engineer at Pinterest, discussed the evolution of the company's iOS Continuous Integration (CI) infrastructure from on-premises physical hardware to a modern cloud-based architecture using AWS EC2 Mac at UnblockConf '21. The transition aimed to alleviate the cumbersome and disruptive maintenance of physical machines and improve the developer experience by enabling the Pinterest team to focus on more impactful efforts. This migration allowed Pinterest to implement a flexible mobile CI architecture with autoscaling groups that adjust to demand, facilitated by AWS services and tools such as RDS, Cloudwatch, Packer, Bazel, Terraform, and Buildkite. The new infrastructure significantly enhanced build speed and reliability, reducing CI-related build failures and upgrade times, thus leading to happier engineers and end users. This transformation showcases the benefits of cloud-hosted architecture in improving operational efficiency and software quality.