Azure Blockchain Service
Azure’s Blockchain Service allows customers to provision blockchain nodes-as-a-service. It allows setting up consortiums that include blockchain nodes from multiple organizations to govern shared resources.
The Blockchain Service has to deal with the complexity of three sources of concurrency interacting with each other: (1) the incoming user requests, (2) asynchronous processing of those requests within the service and (3) reading and reacting to consortium governance data from the blockchain and taking resulting actions within the service. This interaction sometimes led to rare, but serious bugs, that had the potential of stalling the entire blockchain network.
Solution and Coyote’s key advantages
The Blockchain Service code heavily utilized .NET tasks and the corresponding async/await style of programming concurrent systems. Integrating Coyote’s Task-based programming model into the system was easy and required minimal effort. The development team wrote mocks for their external dependencies using Coyote. Writing of mocks is common for any kind of unit testing. The Coyote mocks turned out to be concise and it was easy to express a number of safety and failure scenarios in a localized manner.
Coyote testing helped repro a couple of known safety and liveness bugs in the system. It also revealed a series of bugs in recent changes that had passed code review as well as manual testing. Coyote testing provides confidence that the system will not regress: once a concurrency issue is found and a corresponding Coyote test is put in place, similar issues get caught out immediately in future code changes. This allowed the team to make progress at a rapid pace.