Ruby vs Elixir: Choosing the Right Tool for Your Next Project

Alex Kholodniak Alex Kholodniak
• • 6 min read

I get asked this question a lot: "Should I use Ruby or Elixir for my project?"

The answer is never simple. I've shipped apps in both, and they're good at completely different things. Yes, Elixir's syntax looks like Ruby (José Valim came from the Rails core team), but that's where the similarity ends.

The Quick Version

Ruby (1995) was built for programmer happiness. It reads like English. Rails turned it into the startup language of choice for a decade. GitHub, Shopify, Airbnb - all started on Ruby.

Elixir (2011) runs on Erlang's VM - the thing that keeps WhatsApp and Discord running. It's functional, concurrent, and built for systems that can't go down.

Here's the same code in both:

# Ruby
def greet(name)
  "Hello, #{name}!"
end

puts greet("World")
# Elixir
defmodule Greeter do
  def greet(name) do
    "Hello, #{name}!"
  end
end

IO.puts Greeter.greet("World")

Looks similar, right? Don't be fooled.

Performance: Where They Differ

Ruby's Deal with Concurrency

Ruby has a Global Interpreter Lock. That means only one thread runs Ruby code at a time. For most web apps hitting databases and APIs, this doesn't matter - you're waiting on I/O anyway.

You scale Ruby by running more processes. Puma, Unicorn - they all do this. Works great until it doesn't.

Shopify runs thousands of Ruby processes across their servers. It works. But you're paying for hardware that Elixir wouldn't need.

Elixir's Superpower

Elixir runs millions of tiny processes. Not OS threads - way lighter. Each one has its own memory. No shared state means no locks, no race conditions.

# This actually works
for i <- 1..1_000_000 do
  spawn(fn -> :timer.sleep(10000) end)
end

Try that in Ruby. I'll wait.

Discord moved parts of their stack from Ruby to Elixir and handled millions more connections on the same hardware. Not 10% more. Orders of magnitude more.

Does It Matter?

Benchmarks show Elixir handling 10-100x more concurrent connections than Ruby. But your MVP with 1,000 users? Ruby is fine. Hell, Ruby is fine for 100,000 users if you architect it right.

Actually Writing Code

Ruby Gets Out of Your Way

Ruby reads like English:

users.where(active: true).order(:created_at).limit(10)

5.times { puts "Hello" }

Rails cranks this up to 11. Authentication? gem 'devise'. Background jobs? gem 'sidekiq'. There's a gem for everything.

I can scaffold a full CRUD app in Rails in 45 minutes. That includes auth, database, and tests.

Elixir Makes You Think Differently

Functional programming. You don't change things, you transform them. Took me a while to get it.

def greet(%{name: name, age: age}) when age >= 18 do
  "Hello, adult #{name}"
end

def greet(%{name: name}) do
  "Hello, young #{name}"
end

Pattern matching everywhere. Guards on functions. It's weird at first, then it clicks.

Phoenix is solid, but the ecosystem is smaller. You'll build more yourself. Coming from Rails, expect to spend 3-4 weeks before you're productive.

The Tools

Ruby's got options. IRB or Pry for the REPL. RSpec or Minitest. Rubocop. Bundler. Tons of gems, some great, some abandoned.

Elixir is cleaner. Mix does everything. IEx is great. ExUnit is built-in. Credo for linting. Smaller ecosystem, but what's there is usually maintained.

Ruby feels like a toolbox you've collected over 10 years. Elixir feels like someone designed the whole thing at once.

Community

Ruby

30 years old. Huge community. 400,000+ Stack Overflow questions. Gems for everything - auth (Devise), background jobs (Sidekiq), testing (RSpec), APIs (Grape).

The catch? Half the gems are abandoned. Check the last commit date before you use anything.

Elixir

Smaller, newer, focused. Phoenix for web. Ecto for databases (honestly better than ActiveRecord). LiveView for real-time UI without JavaScript.

The Elixir Forum is active. People actually help. Less noise than Ruby forums.

When to Use Each

Use Ruby For:

MVPs and startups - Ship fast. Validate the idea. Optimize later.

Standard web apps - User accounts, admin panels, CRUD operations. Rails has done this a million times.

Teams that know Ruby - Don't make your team learn functional programming to build a blog.

When you need specific gems - Payment processing, obscure APIs, weird integrations. There's probably a gem.

Good for: SaaS products, e-commerce, content sites, internal tools.

Use Elixir For:

Real-time stuff - Chat, live dashboards, multiplayer games, collaborative editors. Phoenix LiveView is crazy good for this.

High concurrency - Thousands of WebSocket connections. Data streams. API gateways handling tons of requests.

Systems that can't go down - Erlang's "let it crash" philosophy. Supervisors restart failed processes. The system heals itself.

Processing lots of data - ETL pipelines, event streams, data transformation at scale.

Good for: Chat apps, financial systems, IoT platforms, streaming services.

The Performance Thing

Your database is slow. Not your language.

If you're spending 200ms on database queries, saving 5ms by switching to Elixir won't matter. Fix your N+1 queries first. Add caching. Use a CDN. Move slow stuff to background jobs.

THEN, if you're still hitting limits (most apps never do), look at Elixir.

Learning It

Ruby: Week or two if you already code. The syntax makes sense immediately.

Elixir: Month, minimum. Functional programming messes with your head at first. No loops. Everything's immutable. Pattern matching everywhere.

Worth it though. Elixir teaches you to think about concurrency properly. Makes you better at any language.

You Don't Have to Choose One

Lots of companies run both. Ruby for the main app and admin panel. Elixir for real-time features or heavy API traffic.

Gradual migration beats a big rewrite.

What I'd Choose

Ruby:

  • Building a startup or MVP
  • Team doesn't know either language
  • Need to ship this month
  • Standard web app stuff

Elixir:

  • Real-time features or high concurrency
  • Team can handle the learning curve
  • Building something that needs to stay up
  • Processing tons of data

Don't pick based on:

  • What's trendy
  • Benchmark porn (unless you need it)
  • "Modern" vs "old"

Both work. Both make money. Pick what fits your problem.

Bottom Line

Ruby and Elixir solve different problems.

Ruby = rapid development, mature ecosystem, traditional web apps.

Elixir = concurrency, fault tolerance, real-time systems.

I use both. Ruby for prototypes and standard apps. Elixir when I need WebSockets or serious concurrency.

Best language is the one that ships your project.

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