Real-Time Messaging Infrastructure
Handles 5+ million concurrent WebSocket connections per node. Guild state management, presence tracking, and message delivery with sub-100ms latency globally. The definitive Phoenix scale story.
Real-Time Sports Platform
Live game updates and scores, real-time commenting systems during events, push notification infrastructure for millions of fans. High availability during peak sports events.
Business Messaging Platform
Multi-tenant real-time chat connecting businesses with customers. Integration with SMS, Google, and Facebook APIs. Review management and response workflows at scale.
Financial Services Infrastructure
Real-time transaction processing for corporate cards. High-availability payment systems with compliance and audit logging. Fault-tolerant architecture for financial operations.
What Phoenix Developers Actually Build
Before writing your job description, understand what Phoenix developers build in production. Here are real examples from industry leaders:
Real-Time Communication
Discord famously uses Elixir and Phoenix for their real-time infrastructure:
- Handling 5+ million concurrent WebSocket connections per node
- Guild (server) state management with fault-tolerant processes
- Message delivery with sub-100ms latency globally
- Presence tracking for online status across thousands of users per guild
Podium built their business messaging platform with Phoenix:
- Real-time chat between businesses and customers
- Multi-tenant WebSocket connections at scale
- Review management and response workflows
- Integration with SMS, Google, and Facebook messaging APIs
Content & Media
Bleacher Report uses Phoenix for their sports content platform:
- Real-time game updates and scores
- Live commenting systems during games
- Push notification infrastructure for millions of users
- Content management with high availability during peak events
Moz rebuilt their SEO tools with Phoenix:
- Real-time crawl data processing
- Dashboard updates with LiveView
- Background job processing for large-scale analysis
- API serving thousands of concurrent requests
Enterprise & SaaS
Pinterest uses Elixir services for notification delivery:
- Rate limiting and throttling at massive scale
- Reliable delivery pipelines
- Integration with mobile push and email systems
PepsiCo adopted Phoenix for internal applications:
- Real-time dashboard for supply chain visibility
- Employee-facing tools with LiveView interfaces
- Integration with legacy enterprise systems
Brex uses Elixir for financial services infrastructure:
- Real-time transaction processing
- High-availability payment systems
- Compliance and audit logging
Phoenix vs Rails vs Node.js: An Honest Comparison
Understanding how Phoenix compares to alternatives helps you make informed hiring decisions:
Concurrency Model
| Framework | Concurrency Approach | Real-World Impact |
|---|---|---|
| Phoenix/Elixir | Lightweight processes (millions per node) | Discord handles 5M+ concurrent users |
| Rails/Ruby | Thread-based with GIL limitations | Requires more servers for same load |
| Node.js | Event loop, single-threaded | Good for I/O, struggles with CPU tasks |
| Go/Gin | Goroutines (lightweight) | Excellent, but less batteries-included |
What this means for hiring:
Phoenix's concurrency model makes it ideal for real-time applications. If you're building chat, live updates, or IoT systems, Phoenix developers understand distributed systems concepts that transfer across technologies.
Developer Productivity
| Aspect | Phoenix | Rails | Express (Node.js) |
|---|---|---|---|
| Convention over Configuration | Strong | Strong | Minimal |
| Built-in Real-Time | Channels + LiveView | ActionCable (addon) | Socket.io (addon) |
| Database Tooling | Ecto (excellent) | ActiveRecord | Varies (Prisma, etc.) |
| Testing | Built-in, fast | Built-in, slower | Jest/Mocha (setup required) |
Rails developers often find Phoenix familiar due to similar conventions. The learning curve is steeper due to functional programming, but experienced Rails developers become productive in 4-6 weeks.
Talent Pool Reality
| Framework | Talent Supply | Time to Hire | Salary Premium |
|---|---|---|---|
| Phoenix/Elixir | Small, dedicated | 6-10 weeks | +15-25% vs Rails |
| Rails | Large, varied | 3-5 weeks | Baseline |
| Node.js | Very large | 2-4 weeks | Similar to Rails |
The Phoenix talent pool is smaller but often higher quality per candidate. Elixir developers deliberately chose the language—they're typically senior engineers who understand the tradeoffs.
LiveView: The Game Changer
Phoenix LiveView deserves special attention because it's reshaping how teams build interactive applications.
What LiveView Does
LiveView enables rich, real-time user interfaces using server-rendered HTML over WebSockets. Instead of building a React/Vue frontend with REST APIs, developers write Elixir code that automatically updates the browser when server state changes.
When LiveView Shines
- Internal tools and dashboards: Admin panels, monitoring interfaces
- Real-time collaborative features: Shared editors, live cursors, presence
- Forms with complex validation: Multi-step wizards, conditional logic
- Live updates: Notifications, chat, activity feeds
When to Pair with JavaScript
- Highly interactive UIs: Drag-and-drop, complex animations
- Offline-first applications: PWAs that work without connection
- Heavy client-side computation: Image editing, 3D rendering
- Mobile apps: React Native or Flutter remain better choices
What this means for hiring:
LiveView experience indicates a developer who can build full features without frontend framework overhead. For many applications, this means faster development with less complexity. However, if your product requires sophisticated client-side interactions, ensure candidates can integrate JavaScript when needed.
The OTP Advantage: Fault Tolerance by Design
Phoenix runs on OTP (Open Telecom Platform), the battle-tested Erlang framework that powered telecom switches with 99.9999999% uptime. This isn't just marketing—it fundamentally changes how applications handle failure.
Supervision Trees
Elixir applications organize processes into supervision trees. When a process crashes, its supervisor restarts it automatically. This enables the "let it crash" philosophy—rather than writing defensive code for every edge case, you let processes fail and recover.
Example from Discord:
When a Discord guild (server) experiences an issue, only that guild's process crashes and restarts. Other guilds continue operating normally. In traditional architectures, this might bring down the entire service.
Hot Code Reloading
Phoenix applications can be updated without downtime. New code is loaded while the system runs, connections remain active. This capability comes from decades of telecom engineering where downtime was unacceptable.
What this means for hiring:
OTP knowledge separates Phoenix developers who "use the framework" from those who understand its power. Ask candidates about supervision strategies, GenServer patterns, and how they've designed fault-tolerant systems.
Recruiter's Cheat Sheet: Evaluating Phoenix Candidates
Conversation Starters That Reveal Skill Level
| Question | Junior Answer | Senior Answer |
|---|---|---|
| "Why would you choose Phoenix over Rails?" | "It's faster" | "For our real-time notification system, we needed thousands of concurrent connections per node. BEAM's lightweight processes and Phoenix Channels were purpose-built for this. Rails with ActionCable would require significantly more infrastructure." |
| "Explain supervision trees in your applications" | "It's how Elixir handles errors" | "I structure supervisors based on failure domains. Our payment processor uses a one-for-one strategy—if a transaction process fails, only that transaction restarts. The websocket supervisor uses rest-for-one because connection processes depend on shared state." |
| "When would you NOT use LiveView?" | Unsure or "never" | "For our mobile app frontend, we need offline capabilities and 60fps animations. LiveView's latency-dependent model doesn't fit. We use LiveView for internal dashboards and a React Native app for customers." |
Resume Signals That Matter
✅ Look for:
- Specific scale numbers ("handled 100K concurrent connections")
- Mentions of OTP patterns (GenServer, Supervisor, Agent)
- LiveView projects with real-time features
- Contributions to Elixir open source
- Background in Erlang, distributed systems, or telecom
🚫 Be skeptical of:
- "Expert in Elixir/Phoenix" without production examples
- Only tutorial projects (basic blog, to-do app)
- No mention of OTP concepts
- Claims of Phoenix experience without Elixir fundamentals
GitHub Portfolio Signals
Strong indicators:
- Proper supervision tree design in projects
- Use of GenServer for stateful components
- LiveView implementations with real-time features
- Comprehensive test coverage using ExUnit
- Ecto schemas with proper associations and migrations
Red flags:
- Projects that ignore OTP patterns
- No tests or only happy-path tests
- Excessive dependencies for solved problems
- Copy-pasted boilerplate without understanding
The Elixir vs Phoenix Question
When hiring, you'll encounter candidates with strong Elixir skills but limited Phoenix experience, and vice versa. Here's how to evaluate:
Elixir-First Candidates
Developers with deep Elixir/OTP knowledge who haven't used Phoenix extensively. These candidates often come from distributed systems backgrounds.
Strengths: Understand BEAM, concurrency, fault tolerance
Gap: May need time learning Phoenix conventions, LiveView
Verdict: Excellent hires. Phoenix is relatively thin over Elixir—strong Elixir developers become productive in 2-3 weeks.
Phoenix-First Candidates
Developers who learned Phoenix as their entry into Elixir. Often have web development backgrounds (Rails, Django).
Strengths: Know Phoenix patterns, routing, Ecto, possibly LiveView
Gap: May not fully understand OTP supervision, GenServer patterns
Verdict: Good for typical web applications. For real-time or fault-tolerant systems, verify OTP understanding.
The Ideal Candidate
Strong Elixir fundamentals (pattern matching, processes, supervision) combined with Phoenix production experience. These developers understand both the framework conventions and the runtime's unique capabilities.
Common Hiring Mistakes
1. Requiring Years of Phoenix Experience
The mistake: "5+ years Phoenix required"
Reality: Phoenix was released in 2014, but mainstream adoption started around 2017-2019. Many excellent developers have 2-3 years of Phoenix with strong Erlang or other functional programming backgrounds. They often outperform those claiming longer Phoenix tenure.
Better approach: "3+ years Elixir/Phoenix OR 5+ years functional programming with recent Elixir projects"
2. Ignoring Transferable Skills
The mistake: Only considering candidates with Elixir experience.
Reality: The Elixir talent pool is small. Developers with Erlang, Scala, Haskell, or F# backgrounds often transition successfully. Strong Rails developers with functional programming interest also adapt well.
Better approach: Consider functional programming background, distributed systems experience, and willingness to learn Elixir.
3. Undervaluing OTP Knowledge
The mistake: Treating Phoenix like any web framework, ignoring OTP concepts.
Reality: Phoenix's power comes from OTP. A developer who understands supervision, GenServer, and fault tolerance will build significantly more robust systems than one who just knows Phoenix routes and templates.
Better approach: Include OTP questions in interviews. Ask about process design and failure handling.
4. Expecting Full-Stack JavaScript Skills
The mistake: Assuming Phoenix developers are also React/Vue experts because "it's web development."
Reality: LiveView specifically reduces JavaScript needs. Many Phoenix developers chose the stack to avoid heavy frontend frameworks. If you need sophisticated client-side features, be explicit about JavaScript requirements.
Better approach: Clearly separate LiveView needs from JavaScript-heavy frontend work in your job description.