A guide to hiring an Elixir developer
Elixir is a programming language for systems that must handle many users at once and keep running when something goes wrong. It runs on the BEAM, the virtual machine first built for Erlang to run telephone systems. Teams use it for real-time apps, messaging, APIs and long-running background work. An Elixir developer builds and looks after those systems. If your product needs live updates or has to stay up under load, this is the role to look at.
What an Elixir developer actually owns
The work goes beyond writing functions. An Elixir developer decides how the app splits into small processes, how those processes talk to each other and what happens when one of them fails. They design the data and the queries, write tests and read logs from a running system. They also care about the parts users never see: how fast the app starts, how it recovers and how a new engineer finds their way around the code.
Elixir and the BEAM
The BEAM is built to run a very large number of small, separate tasks. Each task has its own memory and talks to others by sending messages, so one failing task does not corrupt the rest. Elixir sits on top with a modern syntax, pattern matching and immutable data, which makes code easy to follow. A good developer knows why the platform behaves the way it does, and uses that on purpose instead of copying habits from other languages.
OTP and supervision
OTP is a set of libraries and design rules that come with Erlang and are used throughout Elixir. It gives names to common patterns, such as a GenServer that holds state and a supervisor that restarts workers. A supervision tree states what should restart when something crashes, and how many times to try before giving up. This is why Elixir systems can stay up while parts of them fail. It is also an easy area to get wrong, so ask candidates to explain how they would arrange the processes in a system you know.
Phoenix and LiveView
Phoenix is the main web framework for Elixir. It handles pages, JSON APIs, sign-in and channels for real-time updates. LiveView lets a developer build live screens in Elixir, where the server pushes changes to the browser without a page reload. Many Elixir products are Phoenix apps. If that is your case, see our Phoenix developers, who focus on that framework every day.
Real-time and messaging systems
Chat, notifications, live dashboards, presence and event streams all depend on moving many small messages quickly. Elixir handles this well, but design still matters. A fast sender can overwhelm a slow receiver, and a message that always fails can block a queue. A good developer plans for back pressure, retries and what to do with a message that cannot be processed. Libraries such as Broadway help with data pipelines, and Oban is a common choice for background jobs.
Ecto and PostgreSQL
Ecto is the database library most Elixir apps use, and PostgreSQL is the database they most often pair it with. A strong developer writes clear queries, avoids calling the database again and again for the same data, and changes tables in a way that does not lock them for long. They also know when a query needs an index. For deeper database work, see our PostgreSQL developers.
Testing
Elixir comes with ExUnit, a built-in test framework, and the language makes small functions easy to test. Good tests check behaviour, run quickly and do not rely on outside services, so a developer uses fakes where needed. Live screens and processes need their own kind of test, and it is worth asking how a candidate handles them. A suite that people trust lets the team change code with confidence.
How an Elixir developer differs from other roles
A back end developer may work in any language and stack, while an Elixir developer knows this one in depth. A Phoenix developer focuses on the web framework, and an Elixir developer may also build messaging, jobs and services that are not mainly web. An Erlang developer works on the same platform, often on older code. Many skilled engineers can move between Elixir and Erlang, so tell us which code you have.
The jobs people hire for
One common brief is a new product with live features, such as chat or a shared dashboard. Another is a messaging or notification service that must handle many connections. A third is taking over an Elixir app that has little documentation and few tests. A fourth is making a slow system steadier. Each needs a different mix of skills, so say which one you have.
When an Elixir developer makes sense
- Your product needs live updates, chat or notifications.
- Many users or devices stay connected at the same time.
- You want one failing task to restart without taking the service down.
- You already have an Elixir codebase that needs someone who knows it.
- You process streams of data or run many background jobs.
If you are building a simple website with a few forms, a more common stack may be easier to hire for and cheaper to run. A developer who tells you that up front is on your side.
Reading an Elixir developer’s background
Ask for a system they built or looked after, how many people used it and what went wrong. Ask them to draw the processes and explain what happens when one crashes. A list of libraries tells you little, since anyone can name Phoenix on a resume. The better sign is someone who can explain a failure they fixed in production and what they changed so it would not come back.
Interview questions to try
- When would you use a GenServer, and when would a plain function do?
- How would you arrange supervisors for a chat service?
- What do you do when a queue of messages grows faster than it is processed?
- How would you find a slow Ecto query in a running app?
- How do you test code that talks to an outside service?
The best answers give reasons and an example from past work. Be wary of a candidate who talks only about how fast Elixir is and never about how they run it.
Run a small paid exercise
Give each finalist the same small task based on your real project. It could be fixing a failing test, adding a small feature to a Phoenix app or reviewing a short module and listing the risks. Pay for the time. Then compare the code, the tests, the questions asked and how clearly each person explains the choices.
Agree how the work is kept healthy
Agree how code is reviewed, how releases are made and who watches the logs and alerts. Ask for a short note on how the app is organised and how to run it locally. Keep the code repository, the servers and the database accounts in your own name, with a separate login for each person. Then nothing is lost if the people change.
Settling in
Give your developer access to the repository, the build tool, the test setup and a staging copy of the app. A weekly call and one shared task board keep progress easy to see. Share the awkward parts early, such as a process that crashes now and then or a query that is slow, because that is where an Elixir specialist adds value fastest.
Mistakes to avoid
- Hiring for the language name alone, and not for experience of running a live system.
- Skipping tests because the platform is known for staying up.
- Putting all state in one process, which becomes a bottleneck.
- Choosing Elixir for a small site that does not need it.
For related skills, see our software engineers for wider product teams, or our back end developers when the language is still open.