A Recoverability-Oriented Analysis for Operations on Cloud Applications

Consumer-initiated sporadic operations on cloud applications, such as deployment, upgrade and reconfiguration, may fail because of the inherent uncertainty of operating in a cloud environment. For example, if a VM is not able to start, operations dependent on that VM will fail. In this paper we propose an approach for analyzing sporadic operations on cloud applications to facilitate recovery. We do this by first creating a process model of the sporadic cloud operation. The Process may not be suitable for recovery operations or the application's deployment architecture since an individual step may be at the wrong level of granularity or a failure may unnecessarily affect multiple steps. We then propose a set of process division criteria for revising an operation process to support recovery. This set of criteria contains four aspects: 1) Atomicity to support the imposition of transactions on portions of the process, 2) Idempotence to allow for re-execution of a failed portion, 3) Granularity to allow reuse of existing steps, 4) Recovery Actions Identifiable to allow proper recovery actions to be taken to recover from the errors occurring during the operation. We demonstrate the feasibility of imposing these criteria by using the rolling upgrade operation in Asgard - a popular cloud management tool for AWS EC2.