A guide to hiring a Scala developer
Scala is a typed programming language that blends functional and object-oriented ideas. It runs mostly on the Java Virtual Machine, so it works with Java libraries and the same hosting as Java apps. Companies use it for services that handle many requests at once, for streaming systems and for large data jobs. A Scala developer builds and keeps those systems healthy. If your product depends on data moving fast and correctly, this is a role worth a close look.
What the job covers
A Scala engineer does more than write functions. They shape the types that describe your business, decide how errors travel through the code and pick the libraries the team will live with for years. They also read stack traces from a busy service, tune memory on the JVM and explain a choice to a colleague who is new to the language. Good ones leave code that others can follow, not code that only they can.
Why the style matters
Scala can be written many ways. One team writes simple code with case classes and plain collections. Another builds on advanced libraries where nearly every call returns an effect. Neither is wrong, but a mismatch hurts. A person who loves heavy abstractions may frustrate a team that wants plain code, and the other way round. Tell us how your own people write Scala today, and we will look for a developer who fits that style.
Typed, functional code in practice
The type system is the main reason to pick Scala. A good developer uses types to rule out invalid states, so a bad order or a missing field fails when the code is built and not when a customer clicks. They prefer immutable data and functions without hidden side effects, which makes code easier to test and to run in parallel. They also know when to stop. A clever type that nobody understands is a cost, not a gain.
Akka and message-driven services
Akka is an open source toolkit for building services from actors, which are small units that pass messages to each other, and from streams. It has been a common base for systems that must handle many connections and recover from failures. Apache Pekko is an open source fork of the Akka code, and some teams use it instead. An engineer who has run these in production can talk about supervision, back pressure and what happens when one node dies. Ask for a real story, not a definition.
Web services and APIs
For HTTP work, Scala teams choose between Play Framework, http4s and Akka HTTP, and some pair them with libraries for JSON and database access. The same good habits apply as anywhere: clear routes, checked input and errors a client can act on. A strong developer also keeps blocking calls off the threads that serve requests, since one slow query can hold up everything behind it.
Spark and data jobs
Apache Spark is written in Scala, and many data engineers write their jobs in it. The work includes reading data from files and queues, joining and cleaning it and writing results to a store. The usual problems are large shuffles, uneven keys and jobs that fit a test laptop but fail on a full run. Our Hadoop developers cover the wider cluster side, including storage and scheduling, and a Scala engineer often works next to them.
Streaming and messaging
Many Scala systems read events from Kafka or a similar queue, process them and write the outcome somewhere else. The hard parts are order, repeats and failure. What if a message arrives twice, or the app stops half way through a batch? Ask candidates how they made such a flow safe, and how they checked that no records were lost.
Testing and builds
Scala has several test libraries, including ScalaTest, MUnit and specs2, and property-based tests can find edge cases a person would not think of. Builds usually run on sbt. Compile times can grow on a large codebase, so a developer who keeps modules small and dependencies tidy saves the whole team time every day.
Scala next to other JVM languages
Java has the biggest hiring pool and the most libraries. Kotlin has a gentler syntax and is common on Android. Scala sits at the typed, functional end, with strong data tools. If you want a functional language that is dynamically typed, our Clojure developers work in that style on the same platform. Tell us what you have today, and we will advise which profile suits the job.
Dedicated or freelance
Searches for Scala help often include the word freelance. For a small, well-defined task that can work. For a system that your business depends on, a dedicated engineer is safer, because few people can read a complex Scala codebase and you do not want that knowledge to walk out of the door. With DigiWorks the person works for your team, full time or part-time from 20 hours a week, and we handle the contract and pay.
When a Scala developer makes sense
- You process large volumes of data or events.
- You run services that must handle many tasks at once.
- You already have a Scala codebase and need someone who can read it.
- You want the compiler to catch more mistakes before release.
- You use Spark and want jobs written by someone who knows its internals.
For a small marketing site or a simple form, Scala would be more than you need. A good engineer says so early.
Reading a Scala resume
Look for a system, not a list of libraries. Ask what the service did, how much data it saw, what failed and how it was fixed. A person who can sketch the design of one real pipeline and name what they would change is worth more than someone who can list every Cats type class.
Interview questions worth asking
- How do you decide between an exception, an Option and an Either?
- Show how you would model an order so a paid order cannot lack an address.
- How do you find out why a Spark job has become slow?
- How would you make an event consumer safe if the same message arrives twice?
- When did you remove a clever abstraction, and why?
Listen for trade-offs and real examples. A confident answer with no downsides deserves a follow-up question.
A small paid task
Give each finalist the same short job drawn from your own work, such as reading a module and listing risks, fixing a flaky test or adding one field through the code. Pay for their time, then compare the code, the questions asked and how clearly each person explains their choices.
Keeping the system maintainable
Agree a code style early, including how far to go with advanced libraries. Run a formatter and a linter on every change. Keep the repository, servers and data accounts in your own company name, with one login for each person, so access is simple to change.
The first weeks
Share the repository, the build setup and a staging copy of the app. Pick one small, real task to ship in the first week so the whole path, from change to release, gets tested. Bring up the code nobody likes to touch early, since a new pair of eyes helps most there.
Mistakes to avoid
- Hiring for library names and ignoring how the person writes code.
- Letting each developer pick a different style.
- Choosing Scala for a job that a simpler language handles well.
- Treating a single expert as the only person who can read the code.
Related help: our back end developers cover other server languages, and our software engineers suit wider product teams.