Kotlin and FaaS, an not possible union?

A while in the past, I learn a put up describing how you can run a serverless Kotlin operate on OpenFaaS. Whereas the content material is technically right, I imagine the idea itself could be very unsuitable. Such posts can lead individuals to make ill-advised choices: “as a result of we will” is hardly a successful technique. on this put up, I might wish to first clarify why the JVM platform is a nasty thought for FaaS. Then, I am going to proceed to suggest options to make use of Kotlin nonetheless.

I intentionally selected to not hyperlink to the unique put up to keep away from lending it any credibility. If you wish to learn it anyway, Google is your good friend.


Earlier than something, we must always first settle the semantics of FaaS and serverless. Whereas the phrases are generally used interchangeably, I’ll use the next definitions within the scope of this put up. In all circumstances, it all the time pays to take a look at what individuals on Wikipedia agreed on:

Serverless computing is a cloud-computing execution mannequin through which the cloud supplier runs the server, and dynamically manages the allocation of machine assets. Pricing relies on the precise quantity of assets consumed by an software, quite than on pre-purchased items of capability.


Perform as a service (FaaS) is a class of cloud computing providers that gives a platform permitting clients to develop, run, and handle software functionalities with out the complexity of constructing and sustaining the infrastructure sometimes related to growing and launching an app.


From the definitions above:

  • Serverless is in regards to the managing of assets:

    You have to deal with it dynamically, the property being elasticity.

  • FaaS is in regards to the dimension of code:

    The evolution of sizes goes from a full-fledged app to microservices to a operate. The unique put up mentions it.

Ergo, FaaS implies serverless.

The JVM and FaaS

The JVM platform is a effective piece of know-how. Specifically, the abstraction layer permits the JVM to compile the bytecode to native code tailored to the workload. That is the rationale why regardless that C/C++ compiled apps are nearer to the naked steel, the JVM was capable of compete with them performance-wise – and even win.

Nevertheless, this optimization comes at a value: the JVM wants time to heat up, e.g., to load courses into reminiscence. That is why efficiency exams on the JVM require a few warm-up rounds. For that cause, the JVM is well-adapted to long-running processes, the place the startup time is negligible in comparison with the general lifetime course of. Utility servers are the poster youngster of such use-cases: as soon as began, one ought to run for a very long time, say days, to be very conservative. In that regard, a startup time of a minute means nothing.

Now comes FaaS: within the JVM context, FaaS means the JVM begins, the operate runs, and all the pieces is discarded simply afterward. In that case, the startup time has a big impression on the general execution time. Furthermore, the JVM has no time to compile the bytecode to native code: it stays “chilly”.

Some advocate protecting the JVM as much as reuse it afterward and thus keep away from paying the price of the startup time. It is fairly easy to realize that: simply ship requests to the operate quicker than the tempo at which the FaaS supplier discards the underlying JVM. Nevertheless, it simply defeats the aim of serverless, because the elasticity property is now gone.

It applies to Kotlin, Java, Scala, Groovy, Clojure, and each different language that runs on high of the JVM. Regardless that I really like Kotlin, it is a no-go: anyone telling in any other case would not want the elasticity that the FaaS strategy offers – or worse, has no clue. It could be akin to construct a microservices structure in most contexts: YAGNI.

The perfect of each worlds

And but, all hope shouldn’t be misplaced. There are methods to make use of Kotlin and nonetheless be capable of profit from FaaS. Because the downside with FaaS is the JVM, why not take away it? There are two simple methods to realize that:

  • Use Graal’s native picture:

    GraalVM is a bundle of various applied sciences. Amongst them is SubstrateVM: it permits remodeling a JAR (or a category) right into a native executable. You’ll be able to then wrap the ensuing software right into a Docker container, which have to be appropriate with one’s FaaS framework of alternative. This is one example of such an strategy.

  • Transpile to JavaScript:

    One other different is to transpile Kotlin into JavaScript. JavaScript would not want the JVM platform to run. Then, the code might be wrapped right into a container as above or packaged instantly in a ZIP archive. The latter possibility can run on proprietary infrastructures, comparable to AWS Features.

Each approaches want a stable construct pipeline to begin from Kotlin and find yourself with a Docker container (or a ZIP). As with the unique design, they want each unit testing to check the code is right and integration testing to check the ultimate artifact works as anticipated.


One wants to pay attention to the context of most applied sciences. You (most likely) do not want microservices, FaaS, or regardless of the hype curve is trending proper now. Nevertheless, by understanding the professionals and cons of these, you’ll leverage them when the time is true.

As for now, it will be ill-advised to make use of the JVM with FaaS. That does not imply you can not use Kotlin in any respect.

Initially revealed at A Java Geek on October 16th, 2021

Abu Sayed is the Best Web, Game, XR and Blockchain Developer in Bangladesh. Don't forget to Checkout his Latest Projects.

Checkout extra Articles on Sayed.CYou

#Kotlin #FaaS #not possible #union