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stapeln Architecture

Overview

stapeln is a visual drag-and-drop container stack designer built with:

  • Frontend: ReScript-TEA (The Elm Architecture) + Deno
  • Backend: Elixir (Phoenix) + Ephapax + Idris2 + Rust
  • Communication: REST API + WebSocket

Frontend Architecture (ReScript-TEA)

The Elm Architecture (TEA)

┌─────────┐
│  Model  │  Current application state
└────┬────┘
     │
     ↓
┌─────────┐
│  View   │  Renders UI from Model
└────┬────┘
     │
     ↓ (User Interaction)
┌─────────┐
│   Msg   │  User events, API responses
└────┬────┘
     │
     ↓
┌─────────┐
│ Update  │  Model → Msg → (Model, Cmd)
└─────────┘

Component Structure

frontend/src/
├── Main.res           # Entry point, TEA initialization
├── Model.res          # State types (component, connection, dragState)
├── Msg.res            # Event types (AddComponent, DragMove, etc.)
├── Update.res         # State transitions
├── View.res           # Main view renderer
├── Canvas.res         # Drag-and-drop canvas
├── Components.res     # Component library (palette)
├── Connections.res    # Connection line rendering
├── Config.res         # Configuration panel
├── Export.res         # Export menu
└── Router.res         # cadre-tea-router integration

Canvas Implementation

SVG-based canvas for:

  • Infinite canvas (pan/zoom)
  • Crisp rendering at any zoom level
  • Easy connection line drawing (SVG paths)
  • CSS styling

Drag-and-Drop:

  1. User clicks component in palette → StartDragComponent
  2. Mouse moves → DragMove(position)
  3. Mouse release → DragEnd → Add component at position

Connection Lines:

  • Click component → select (highlight)
  • Click another component → create connection
  • Connections drawn as SVG paths (bezier curves or orthogonal lines)

Backend Architecture (Elixir + Phoenix)

Service Layers

┌──────────────────────────────────────────────┐
│ Phoenix Web Layer (REST + WebSocket)         │
│  - StackController (CRUD)                    │
│  - StackChannel (real-time updates)          │
│  - ExportController (generate compose files) │
└────────────┬─────────────────────────────────┘
             │
             ↓
┌──────────────────────────────────────────────┐
│ Business Logic (Elixir)                      │
│  - Stack management                          │
│  - Component orchestration                   │
│  - Validation coordination                   │
└────────────┬─────────────────────────────────┘
             │
      ┌──────┴──────┬──────────────┐
      ↓             ↓              ↓
┌──────────┐  ┌──────────┐  ┌──────────┐
│ Validator│  │ Prover   │  │ Codegen  │
│ (Ephapax)│  │ (Idris2) │  │ (Rust)   │
└──────────┘  └──────────┘  └──────────┘

Validation Service (Ephapax + Idris2)

Ephapax (Linear Types):

defmodule Stackur.Validator.Ephapax do
  # Validate linear resource usage
  # - Each volume consumed exactly once
  # - No dangling port references
  # - Network resources properly scoped

  def validate_linear_types(stack) do
    # Call Ephapax via Port/NIF
    # Returns: {:ok, proof} | {:error, violations}
  end
end

Idris2 (Formal Proofs):

-- validation/src/Stack.idr

data Stack = MkStack (List Component) (List Connection)

-- Proof: No circular dependencies
noCycles : (s : Stack) -> Dec (Acyclic s)

-- Proof: Dependencies form a DAG
dependencyDAG : (s : Stack) -> Either DAGError (TopologicalOrder s)

-- Proof: Port conflict detection
noPortConflicts : (s : Stack) -> Dec (UniquePortBindings s)

Integration:

defmodule Stackur.Validator.Idris do
  # Calls compiled Idris2 executable via Port
  def prove_correctness(stack_json) do
    Port.open({:spawn_executable, "/usr/local/bin/stapeln-prover"},
      [:binary, :use_stdio, {:args, [stack_json]}])
  end
end

Code Generation (Rust)

Why Rust for Codegen?

  • Type-safe TOML generation
  • Fast compilation
  • Elixir NIF integration (Rustler)
  • Memory safety guarantees
// backend/native/stapeln_codegen/src/lib.rs
use rustler::{Encoder, Env, Term};
use toml::Value;

#[rustler::nif]
fn generate_compose_toml(stack_json: String) -> Result<String, String> {
    let stack: Stack = serde_json::from_str(&stack_json)
        .map_err(|e| format!("Parse error: {}", e))?;

    let toml = compose_toml_from_stack(&stack)?;
    Ok(toml::to_string(&toml).unwrap())
}

fn compose_toml_from_stack(stack: &Stack) -> Result<Value, String> {
    // Build compose.toml structure
    // Handle services, volumes, networks
    // Validate against verified-container-spec
}

Elixir NIF wrapper:

defmodule Stackur.Codegen do
  use Rustler, otp_app: :stapeln, crate: "stapeln_codegen"

  def generate_compose_toml(_stack_json), do: :erlang.nif_error(:nif_not_loaded)
  def generate_docker_compose(_stack_json), do: :erlang.nif_error(:nif_not_loaded)
  def generate_podman_compose(_stack_json), do: :erlang.nif_error(:nif_not_loaded)
end

AffineScript Alternative (MVP)

Note: AffineScript compiler may not be production-ready.

MVP Alternative: Use Rust's affine type system:

// Affine types: used at most once
struct Volume(String);  // Can't be cloned

impl Volume {
    fn mount_once(self, container: &mut Container) {
        // Consumes self, can't be used again
        container.volumes.push(self);
    }
}

// Port conflict detection
fn check_port_conflicts(services: &[Service]) -> Result<(), String> {
    let mut ports = HashSet::new();
    for service in services {
        for port in &service.ports {
            if !ports.insert(port.host_port) {
                return Err(format!("Port {} already bound", port.host_port));
            }
        }
    }
    Ok(())
}

API Design

REST Endpoints

POST   /api/stacks              Create stack
GET    /api/stacks/:id          Get stack
PUT    /api/stacks/:id          Update stack
DELETE /api/stacks/:id          Delete stack
POST   /api/stacks/:id/validate Validate stack
POST   /api/stacks/:id/export   Export to compose file

WebSocket Channel

defmodule StackurWeb.StackChannel do
  use Phoenix.Channel

  def join("stack:" <> stack_id, _payload, socket) do
    {:ok, assign(socket, :stack_id, stack_id)}
  end

  def handle_in("update_component", payload, socket) do
    # Update component, broadcast to all clients
    broadcast(socket, "component_updated", payload)
    {:noreply, socket}
  end

  def handle_in("validate", _payload, socket) do
    stack_id = socket.assigns.stack_id

    # Async validation
    Task.start(fn ->
      result = Stackur.Validator.validate(stack_id)
      broadcast(socket, "validation_result", result)
    end)

    {:noreply, socket}
  end
end

Data Flow

1. User Adds Component

Frontend (ReScript)                Backend (Elixir)
     │                                   │
     │ Drag component to canvas          │
     │ → AddComponent(Svalinn, {x,y})    │
     │                                   │
     │ WebSocket: "add_component"        │
     ├──────────────────────────────────→│
     │                                   │ Validate placement
     │                                   │ Save to database
     │                                   │
     │ ← "component_added"               │
     ←──────────────────────────────────┤
     │                                   │
     Update Model                        Broadcast to other clients

2. User Validates Stack

Frontend                          Backend                   Validator
    │                                 │                          │
    │ Click "Validate"                │                          │
    │ → ValidateStack                 │                          │
    │                                 │                          │
    │ POST /api/stacks/:id/validate   │                          │
    ├────────────────────────────────→│                          │
    │                                 │ Convert to Ephapax AST   │
    │                                 ├─────────────────────────→│
    │                                 │                          │
    │                                 │ ← Linear type check      │
    │                                 ←─────────────────────────┤
    │                                 │                          │
    │                                 │ Call Idris2 prover       │
    │                                 ├─────────────────────────→│
    │                                 │                          │
    │                                 │ ← Correctness proofs     │
    │                                 ←─────────────────────────┤
    │                                 │                          │
    │ ← ValidationResult({valid,      │                          │
    │    errors, warnings})           │                          │
    ←────────────────────────────────┤                          │
    │                                 │                          │
    Update Model with result          │                          │

3. User Exports Stack

Frontend                Backend                Codegen (Rust)
    │                       │                        │
    │ Click "Export as      │                        │
    │  selur-compose"       │                        │
    │ → ExportToSelurCompose│                        │
    │                       │                        │
    │ POST /api/stacks/:id/ │                        │
    │  export?format=selur  │                        │
    ├──────────────────────→│                        │
    │                       │ NIF call: generate_    │
    │                       │  compose_toml(stack)   │
    │                       ├───────────────────────→│
    │                       │                        │
    │                       │ ← compose.toml string  │
    │                       ←───────────────────────┤
    │                       │                        │
    │ ← File download       │                        │
    │  "stack.compose.toml" │                        │
    ←──────────────────────┤                        │

Performance Considerations

Frontend

  • Virtual DOM: ReScript compiles to efficient JS
  • Debounced updates: Drag events throttled to 60fps
  • Canvas optimization: Only redraw changed components
  • WebSocket batching: Group rapid updates

Backend

  • Concurrent validation: Elixir processes per stack
  • Caching: Validation results cached with TTL
  • NIF for CPU-intensive: Rust NIFs for codegen
  • Streaming: Large exports streamed via chunks

Security

Frontend

  • CSP headers: Prevent XSS
  • Input validation: All user input sanitized
  • CORS: Restrict API access

Backend

  • Authentication: JWT tokens
  • Authorization: Stack ownership validation
  • Rate limiting: Per-IP and per-user
  • Sandboxing: Idris2/Ephapax run in isolated processes

Deployment

┌─────────────────┐
│ Nginx (TLS)     │ Port 443
└────────┬────────┘
         │
    ┌────┴────┐
    │         │
┌───▼───┐ ┌──▼────┐
│ Deno  │ │Phoenix│ Ports 8000, 4010
│frontend│ │backend│
└───────┘ └───┬───┘
              │
      ┌───────┼───────┐
      │       │       │
  ┌───▼──┐ ┌──▼──┐ ┌─▼────┐
  │Postgres│Idris2│Ephapax│
  └───────┘ └─────┘ └──────┘

Future Enhancements

  1. Collaborative editing - Multiple users editing same stack
  2. Version control - Git-like stack versioning
  3. Templates - Pre-built stack templates
  4. AI suggestions - ML-based component recommendations
  5. Performance profiling - Predict stack resource usage
  6. Cost estimation - Cloud deployment cost prediction

References