xAFCL: Run Scalable Function Choreographies Across Multiple FaaS Systems
Sasko Ristov, Stefan Pedratscher, Thomas Fahringer
Abstract
Most well-known cloud providers offer advanced support for serverless applications that goes beyond single function invocation by enabling developers to build entire workflows, which are known as serverless function choreographies (FCs). Current support for FCs by many FaaS systems uncovered important problems including maximum number of parallel function executions, unexpected considerable delays, and provider lock-in. These limitations can result in longer execution times or even failure to execute individual functions or entire FCs. To overcome some of these limitations, we introduce a scalable middleware service xAFCL that can schedule and execute different functions of the same FC across multiple FaaS systems (currently supporting all top five providers). In order to support scheduling under xAFCL, we introduce a novel FaaS model which estimates the completion time of functions by considering FaaS system limitations, submission delays, and overheads for executing functions. Experimental results demonstrate that xAFCLs FaaS model shows very low inaccuracy of up to 2.9% for AWS and 20% for IBM for real-life BWA data-bound FC that uses S3. Moreover, xAFCL outperforms an earliest start time (EST) scheduler by up to 43% for makespan and 2.7x for throughput.