In one embodiment, a scale out policy service for processing a stream of messages includes a distributed stream processing computation system comprising distributed stream processing nodes, a distributed storage system, and a rules engine. A stream processing engine of the distributed stream processing computation system can receive the stream of messages comprising requests and/or events, and assign a first message to be processed by one or more distributed stream processing nodes based on one or more properties of the message. The one or more distributed stream processing nodes can be communicably connected to the distributed storage system and/or the rules engine to provide (1) an answer in response to the first message and/or (2) cause an action to be executed based on the first message.