Serverless platforms aim to simplify the deployment, scaling, and management of cloud applications. Serverless applications are inherently distributed, and are executed using shortlived ephemeral processes. The use of short-lived ephemeral processes simplifies application scaling and management, but also means that existing approaches to monitoring distributed systems and detecting bugs cannot be applied to serverless applications. In this paper we propose Watchtower, a framework that enables runtime monitoring of serverless applications. Watchtower takes program properties as inputs, and can detect cases where applications violate these properties. We design Watchtower to minimize application changes, and to scale at the same rate as the application. We achieve the former by instrumenting libraries rather than application code, and the latter by structuring Watchtower as a serverless application. Once a bug is found, developers can use the Watchtower debugger to identify and address the root cause of the bug.

The rise of serverless computing provides an opportunity to rethink cloud security. We present an approach for securing serverless systems using a novel form of dynamic information flow control (IFC). We show that in serverless applications, the termination channel found in most existing IFC systems can be arbitrarily amplified via multiple concurrent requests, necessitating a stronger termination-sensitive non-interference guarantee, which we achieve using a combination of static labeling of serverless processes and dynamic faceted labeling of persistent data. We describe our implementation of this approach on top of JavaScript for AWS Lambda and OpenWhisk serverless platforms, and present three realistic case studies showing that it can enforce important IFC security properties with modest overhead.