Backend6 min read

Elixir & Phoenix

Build fault-tolerant real-time systems with Elixir and Phoenix - processes, OTP supervision trees, Phoenix LiveView, and Ecto for database access.

ElixirPhoenixErlangOTPReal-Time

skill: Elixir & Phoenix category: Backend tags: [Elixir, Phoenix, Erlang, OTP, Real-Time] readingTime: 6

Elixir's OTP supervision trees make fault-tolerant systems natural - individual processes crash and restart without affecting the system. This, combined with the actor model and immutable data, makes Elixir uniquely suited for real-time, concurrent systems (chat, gaming, IoT). Phoenix LiveView brings this to interactive UIs without JavaScript frameworks.

Workflow

Think in processes and pattern matchingElixir processes are isolated (no shared memory), lightweight (millions can run simultaneously), and communicate via message passing. Pattern matching is Elixir's primary control flow mechanism.
Design supervision treesOTP supervisors monitor processes and restart them on failure - "let it crash" philosophy. Hierarchical supervision isolates failures so one crashing process doesn't bring down the system.
Build real-time UIs with Phoenix LiveViewPhoenix LiveView enables rich, interactive UIs over WebSocket with server-rendered HTML - no separate JavaScript framework, no client-side state management.
Query databases with EctoEcto is Elixir's database library - queryable, composable, and explicit. Unlike ActiveRecord, Ecto separates schemas, changesets (validation), and queries.
Benchmark Elixir's concurrency modelElixir's process model enables millions of concurrent users on a single server. Understanding when this matters vs. when simpler models suffice guides adoption decisions.

Output Format

Elixir: pattern matching dispatch, GenServer stateful processes, Supervisor one_for_one tree, Phoenix LiveView with phx-click, Ecto changeset + preload for N+1 prevention.

Pattern match: def handle(%{type: "order"} = event)
GenServer: start_link + handle_call/handle_cast/handle_info
Supervisor: [Repo, PubSub, Endpoint] with :one_for_one
LiveView: mount + handle_event + render with ~H sigil
Ecto: changeset(user, attrs) |> validate_required |> Repo.insert()

Examples

Input

Output

Edge Cases & Gotchas

Let it crash vs. defensive programming - Let it crash means: don't write defensive error handling inside processes - let them crash, the supervisor will restart. But do handle expected errors (user input validation, external API errors) explicitly.
Ecto transaction isolation - Ecto.Multi runs multiple operations in a single database transaction. On any failure, Ecto.Multi rolls back all operations - use it for multi-step business transactions.
Hot code upgrades - Erlang/OTP supports hot code upgrades - deploying new code without stopping the server. This is a powerful but complex feature requiring careful OTP state management.
LiveView disconnection handling - If the WebSocket disconnects (mobile network, sleep), LiveView gracefully reconnects and patches the DOM to match server state. No client-side state reconciliation needed.

When to Break These Rules

Use Node.js or Python instead of Elixir for standard CRUD APIs without real-time requirements - Elixir's unique value is concurrency and fault tolerance, not raw HTTP throughput.
Skip Phoenix LiveView for fully client-side applications (offline-first, complex animations, React-heavy) where the server-rendered model adds friction.

Reference Files

https://hexdocs.pm/elixir/
https://www.phoenixframework.org/