DADI: Block-Level Image Service for Agile and Elastic Application Deployment

Businesses increasingly need agile and elastic computing infrastructure to respond quickly to real world situations. By offering efficient process-based virtualization and a layered image system, containers are designed to enable agile and elastic application deployment. However, creating or updating large container clusters is still slow due to the image downloading and unpacking process. In this paper, we present DADI Image Service, a block-level image service for increased agility and elasticity in deploying applications. DADI replaces the waterfall model of starting containers (downloading image, unpacking image, starting container) with fine-grained on-demand transfer of remote images, realizing instant start of containers. DADI optionally relies on a peer-to-peer architecture in large clusters to balance network traffic among all the participating hosts. DADI efficiently supports various kinds of runtimes including cgroups, QEMU, etc., further realizing ``build once, run anywhere''. DADI has been deployed at scale in the production environment of Alibaba, serving one of the world's largest ecommerce platforms. Performance results show that DADI can cold start 10,000 containers on 1,000 hosts within 4 seconds.