Histrio: Actor-based programming and correctness guarantees for serverless environments

The serverless paradigm has gained significant traction for cloud applications, offering scalability while offloading infrastructure management and resource provisioning to providers. However, its adoption introduces a shift in programming model, adding complexity to software development. In Function-as-a-Service (FaaS), functions are stateless, requiring developers to manage external storage, concurrency control, and failure handling diverting focus from business logic. This paper presents Histrio, a programming model and execution environment that realizes the actor model on top of a standard serverless stack, comprising a FaaS platform to execute actors, a managed database to persist actors state, and a queuing service to notify message delivery. Crucially, these underlying technologies are entirely abstracted away, providing developers with a pure actor-based programming interface that is agnostic to the implementation details. By adopting the actor model, Histrio encapsulates state within actors and enforces isolation by construction, while providing exactly-once execution semantics even in the presence of failures. It further enriches the actor model with query-like features that optimize common state access patterns. The result is a system that combines the convenience of the actor model with the benefits of serverless deployments, enabling stateful applications with strong isolation and fault tolerance guarantees.