A Language-based Serverless Function Accelerator
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Serverless computing is an approach to cloud computing that allows programmers to run serverless functions in response to short-lived events. Cloud providers bill functions at sub-second granularity, provide transparent elasticity, and completely manage operating system resources. Unfortunately, today's serverless platforms exhibit high tail latency, because it is difficult to maximize resource utilization while minimizing operating costs. We present Containerless, which is a serverless function accelerator that lowers the latency and resource utilization of typical serverless functions written in JavaScript. In Containerless, a serverless function starts execution in a container, and is instrumented to build an execution trace tree (similar to a tracing JIT compiler). After the function processes a number of events, Containerless extracts the trace tree, compiles it to safe subset of Rust, and then processes subsequent events more efficiently in Rust, using language-based sandboxing instead of the container sandbox. If the Rust code receives an event that triggers an unknown or unsupported execution path, Containerless aborts the language-based sandbox and restarts execution in the container. This approach works because serverless platforms already require functions to tolerate re-execution for fault tolerance. To a serverless function, a re-execution caused by Containerless is observationally equivalent to a re-execution caused by a fault. Our evaluation shows that Containerless can significantly decrease the latency and resource utilization usage of serverless functions, e.g., increasing throughput of I/O bound functions by 3.4x (geometric mean speedup). We also show that the impact of tracing is negligible and that Containerless seamlessly switches between its two modes of sandboxing.
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