Communications of the ACM

plications. From an infrastructure
perspective, serverless and more tra-
ditional architectures may be used in-
terchangeably or in combination. The
determination of when to use server-
less will likely be influenced by other
non-functional requirements, such as
the amount of control over operations
tion written in JavaScript could take as
input a JSON object as the first param-
eter, and context as the second.

Use Case 2:

Current Cloud Provider Serverless offerings support a wide variety programming languages, including Java, Python, Swift, C#, and Node.js. Some of the platforms also support extensibility mechanisms for code written in any language as long as it is packaged in a Docker image that supports a well-defined API.

API Composition

Consider a mobile app that sequentially invokes a geolocation, weather, and language translation APIs to render the weather forecast for a user’s current location. A short serverless function can be used to invoke these APIs. Thus the mobile app avoids invoking multiple APIs over a potentially resource constrained mobile network connection, and offloads the filtering and aggregation logic to the backend. Glucon, for example, used serverless in its conference scheduler application to minimize client code, and avoid disruptions.

Due to the limited and stateless nature of serverless functions, and its suitability for composition of APIs, cloud providers are offering an ecosystem of value added services that support the different functionalities a developer may require, and is essential for production ready applications. For example, a function may need to retrieve state from permanent storage, such as a file server or database, another may use a machine learning service to perform some text analysis or image recognition. While the functions themselves may scale due to the serverless guarantees, the underlying storage system itself must provide reliability and QoS guarantees to ensure smooth operation.

A serverless anti-pattern of offloading API calls from mobile app to backend.

Mobile app
Lat/long
coordinates

3 day weather
forecast in French

def main(dict):
  zip = gis.geo ToZip(dict.get("coords"))
  forecasts = weather.forecast(zip)
  firstThreeDays = forecasts[0:3]
  translated = language.translate(firstThreeDays , ”en", ”fr")
  return {"forecast": filter(translated)}

Coord ToZipCode service Weather forecast service Language translation service

Tools and Frameworks

Note the main function is acting as an orchestrator that is waiting for a response from a function before invoking another, thus incurring a cost of execution while the function is basically waiting for I/O. Such a pattern of programming is referred to as a serverless anti-pattern.

One of the major challenges slowing the adoption of serverless is the lack of tools and frameworks. The tools and frameworks currently available can be categorized as follows: development, testing, debugging, deployment. Several solutions been proposed to deal with these categories.

The serverless programming approach would be to encapsulate each API call as serverless function, and the chain the invocation of these functions in a sequence. The sequence itself behaves as a composite function.

Offloading API calls and glue logic from mobile app to backend.

Mobile App

Almost all cloud providers provide a cloud-based IDE, or extensions/pl-ugins to popular IDEs that allows the developer to code and deploy serverless functions. They also provide a local containerized environment with an SDK that allows the developer to develop and test locally serverless functions before deploying it in a cloud setting. To enable debugging, function execution logs are available to the developer and recent tools such as AWS X-Rayi allow developers to detect potential causes of the problem. 22 Finally, there are open source frameworksj that allow developers to define serverless func-

Lat/long 3 day weather
forecast in French
Coord ToZipCode service Weather Forecast Service Language Translation Service
composite function

More complex orchestrations can use technologies like AWS Step Functions and IBM Composer to prevent serverless anti-patterns but may incur additional costs due to the services.