Towards Choreographic-Based Monitoring

Distributed programs are hard to get right because they are required to be open, scalable, long-running, and dependable. In particular, the recent approaches to distributed software based on (micro-) services, where different services are developed independently by disparate teams, exacerbate the problem. Services are meant to be composed together and run in open contexts where unpredictable behaviours can emerge. This makes it necessary to adopt suitable strategies for monitoring the execution and incorporate recovery and adaptation mechanisms so to make distributed programs more flexible and robust. The typical approach that is currently adopted is to embed such mechanisms within the program logic. This makes it hard to extract, compare and debug. We propose an approach that employs formal abstractions for specifying failure recovery and adaptation strategies. Although implementation agnostic, these abstractions would be amenable to algorithmic synthesis of code, monitoring, and tests. We consider message-passing programs (a la Erlang, Go, or MPI) that are gaining momentum both in academia and in industry. We first propose a model which abstracts away from three aspects: the definition of formal behavioural models encompassing failures; the specification of the relevant properties of adaptation and recovery strategy; and the automatic generation of monitoring, recovery, and adaptation logic in target languages of interest. To show the efficacy of our model, we give an instance of it by introducing reversible choreographies to express the normal forward behaviour of the system and the condition under which adaptation has to take place. Then we show how it is possible to derive Erlang code directly from the global specification