Modern software projects have been increasingly using cloud services as important components. The cloud-based programming practice greatly simplifies software development by harvesting cloud benefits (e.g., high availability and elasticity). However, it imposes new challenges for software testing and analysis, due to opaqueness of cloud backends and monetary cost of invoking cloud services for continuous integration and deployment. As a result, cloud emulators are developed for offline development and testing, before online testing and deployment. This paper presents a systematic analysis of cloud emulators from the perspective of cloud-based software testing. Our goal is to (1) understand the discrepancies introduced by cloud emulation with regard to software quality assurance and deployment safety and (2) address inevitable gaps between emulated and real cloud services. The analysis results are concerning. Among 255 APIs of five cloud services from Azure and Amazon Web Services (AWS), we detected discrepant behavior between the emulated and real services in 94 (37 %) of the APIs. These discrepancies lead to inconsistent testing results, threatening deployment safety, introducing false alarms, and creating debuggability issues. The root causes are diverse, including accidental implementation defects and essential emulation challenges. We discuss potential solutions and develop a practical mitigation technique to address discrepancies of cloud emulators for software testing.

Low Earth Orbit (LEO) satellite networks, such as Starlink, provide global internet access and currently serve content to millions of users. Recent work has shown that existing network infrastructures, such as Content Delivery Networks (CDNs), are not well-suited to satellite network architectures. Traditional terrestrial CDNs degrade performance for satellite network users and do not alleviate the congestion in the ground-satellite links. We design StarCDN, a new CDN architecture that caches content in space to improve user experience and reduce ground-satellite bandwidth usage. The fundamental challenge in designing StarCDN lies in the orbital motion of satellites, which causes each satellite's coverage area to change rapidly, serving vastly different regions (e.g., US and Europe) within minutes. To address this, we introduce new consistent hashing and relayed fetching schemes tailored to LEO satellite networks. Our design enables cached content to flow in the opposite direction of the orbital motion to counter satellite motion. We evaluate StarCDN against multiple baselines using real-world traces from Akamai. Our evaluation demonstrates that StarCDN can reduce the ground-to-satellite bandwidth utilization by 80% and improve user-perceived latency by 2.5X. Further, we make available an open-source trace generator, SpaceGEN, for realistic simulations of satellite-based CDNs.