skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.


Title: Sift: Using Refinement-guided Automation to Verify Complex Distributed Systems
Distributed systems are hard to design and implement correctly. Recent work has tried to use formal verification techniques to provide rigorous correctness guarantees. These works present a hard choice, though. One must either opt for the power of refinement-based approaches like IronFleet and Verdi, at the cost of large amounts of manual effort; or choose the more automated approach of I4, IC3PO, SWISS and DistAI which give up the ability to prove refinement and the power and scalability that come with it. We propose an alternative approach, Sift, that combines the power of refinement with the ability to automate proofs. Sift is a two-tier methodology that uses a new technique, refinement-guided automation, to leverage automation in a refinement proof and a divide-and-conquer technique to split a system into more refinement layers when necessary. This combination advances the frontier of what systems can be proven correct using a high degree of automation. Contrary to what was possible before, our evaluation shows that our novel approach allows us to prove the correctness of a number of systems with little manual effort, and to extend our proofs to include not just the protocols, but also an executable distributed implementation of these systems.  more » « less
Award ID(s):
2018915
PAR ID:
10358924
Author(s) / Creator(s):
; ; ; ; ; ;
Date Published:
Journal Name:
2022 USENIX Annual Technical Conference
Page Range / eLocation ID:
151-166
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Elsman, Martin (Ed.)
    Protocols to ensure that messages are delivered in causal order are a ubiquitous building block of distributed systems. For instance, distributed data storage systems can use causally ordered message delivery to ensure causal consistency, and CRDTs can rely on the existence of an underlying causally-ordered messaging layer to simplify their implementation. A causal delivery protocol ensures that when a message is delivered to a process, any causally preceding messages sent to the same process have already been delivered to it. While causal delivery protocols are widely used, verification of their correctness is less common, much less machine-checked proofs about executable implementations. We implemented a standard causal broadcast protocol in Haskell and used the Liquid Haskell solver-aided verification system to express and mechanically prove that messages will never be delivered to a process in an order that violates causality. We express this property using refinement types and prove that it holds of our implementation, taking advantage of Liquid Haskell’s underlying SMT solver to automate parts of the proof and using its manual theorem-proving features for the rest. We then put our verified causal broadcast implementation to work as the foundation of a distributed key-value store. 
    more » « less
  2. This article presents liquid resource types, a technique for automatically verifying the resource consumption of functional programs. Existing resource analysis techniques trade automation for flexibility -- automated techniques are restricted to relatively constrained families of resource bounds, while more expressive proof techniques admitting value-dependent bounds rely on handwritten proofs. Liquid resource types combine the best of these approaches, using logical refinements to automatically prove precise bounds on a program's resource consumption. The type system augments refinement types with potential annotations to conduct an amortized resource analysis. Importantly, users can annotate data structure declarations to indicate how potential is allocated within the type, allowing the system to express bounds with polynomials and exponentials, as well as more precise expressions depending on program values. We prove the soundness of the type system, provide a library of flexible and reusable data structures for conducting resource analysis, and use our prototype implementation to automatically verify resource bounds that previously required a manual proof. 
    more » « less
  3. This article presents liquid resource types, a technique for automatically verifying the resource consumption of functional programs. Existing resource analysis techniques trade automation for flexibility – automated techniques are restricted to relatively constrained families of resource bounds, while more expressive proof techniques admitting value-dependent bounds rely on handwritten proofs. Liquid resource types combine the best of these approaches, using logical refinements to automatically prove precise bounds on a program’s resource consumption. The type system augments refinement types with potential annotations to conduct an amortized resource analysis. Importantly, users can annotate data structure declarations to indicate how potential is allocated within the type, allowing the system to express bounds with polynomials and exponentials, as well as more precise expressions depending on program values. We prove the soundness of the type system, provide a library of flexible and reusable data structures for conducting resource analysis, and use our prototype implementation to automatically verify resource bounds that previously required a manual proof. 
    more » « less
  4. Distributed systems are notoriously difficult to design and implement correctly. Formal verification provides correctness proofs, and has recently been successfully applied to various distributed systems. At the heart of a typical formal verification is a computer-checked proof with an inductive invariant. Finding this inductive invariant is the hardest part of the proof: a part that is currently undertaken manually by the developer and is responsible for most of the effort associated with formal verification. In this paper, we present a new approach: Incremental Inference of Inductive Invariants (I4), to automatically generate inductive invariants for distributed protocols. We start from a simple idea: the inductive invariant of a finite instance of the protocol must be an instance of a general inductive invariant for the infinite distributed protocol. In I4, we instantiate a finite instance of the protocol, work out the finite inductive invariant of this instance, then figure out the general inductive invariant as a generalization of the finite invariant. Our experiments show that I4 can finish the general proof of correctness of several systems with minimal human effort. 
    more » « less
  5. Proving the correctness of a distributed protocol is a challenging endeavor. Central to this task is finding an inductive invariant for the protocol. Currently, automated invariant inference algorithms require developers to describe protocols using a restricted logic. If the developer wants to prove a protocol expressed without these restrictions, they must devise an inductive invariant manually. We propose an approach that simplifies and partially automates finding the inductive invariant of a distributed protocol, as well as proving that it really is an invariant. The key insight is to identify an invariant taxonomy that divides invariants into Regular Invariants, which have one of a few simple low-level structures, and Protocol Invariants, which capture the higher-level host relationships that make the protocol work. Building on the insight of this taxonomy, we describe the Kondo methodology for proving the correctness of a distributed protocol modeled as a state machine. The developer first manually devises the Protocol Invariants by proving a synchronous version of the protocol correct. In this simpler version, sends and receives are replaced with atomic variable assignments. The Kondo tool then automatically generates the asynchronous protocol description, Regular Invariants, and proofs that the Regular Invariants are inductive on their own. Finally, Kondo combines these with the synchronous proof into a draft proof of the asynchronous protocol, which may then require a small amount of user effort to complete. Our evaluation shows that Kondo reduces developer effort for a wide variety of distributed protocols. 
    more » « less