Smart Placement Configuration

Smart Placement Configuration

wrangler.jsonc Setup

{
  "$schema": "./node_modules/wrangler/config-schema.json",
  "placement": {
    "mode": "smart",
  },
}

Placement Mode Values

Note: Smart Placement vs Explicit Placement are separate features. Smart Placement (mode: "smart") uses automatic analysis. For manual placement control, see explicit placement options (region, host, hostname fields - not covered in this reference).

Frontend + Backend Split Configuration

Frontend Worker (No Smart Placement)

// frontend-worker/wrangler.jsonc
{
  "name": "frontend",
  "main": "frontend-worker.ts",
  // No "placement" - runs at edge
  "services": [
    {
      "binding": "BACKEND",
      "service": "backend-api",
    },
  ],
}

Backend Worker (Smart Placement Enabled)

// backend-api/wrangler.jsonc
{
  "name": "backend-api",
  "main": "backend-worker.ts",
  "placement": {
    "mode": "smart",
  },
  "d1_databases": [
    {
      "binding": "DATABASE",
      "database_id": "xxx",
    },
  ],
}

Requirements & Limitations

Requirements

• Wrangler version: 2.20.0+
• Analysis time: Up to 15 minutes
• Traffic requirements: Consistent multi-location traffic
• Workers plan: All plans (Free, Paid, Enterprise)

What Smart Placement Affects

CRITICAL LIMITATION - Smart Placement ONLY Affects fetch Handlers:

Smart Placement is fundamentally limited to Workers with default fetch handlers. This is a key architectural constraint.

• ✅ Affects: fetch event handlers ONLY (the default export's fetch method)
• ❌ Does NOT affect:
  • RPC methods (Service Bindings with WorkerEntrypoint - see example below)
  • Named entrypoints (exports other than default)
  • Workers without fetch handlers
  • Queue consumers, scheduled handlers, or other event types

Example - Smart Placement ONLY affects fetch:

// ✅ Smart Placement affects this:
export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    // This runs close to backend when Smart Placement enabled
    const data = await env.DATABASE.prepare('SELECT * FROM users').all()
    return Response.json(data)
  },
}

// ❌ Smart Placement DOES NOT affect these:
export class MyRPC extends WorkerEntrypoint {
  async myMethod() {
    // This ALWAYS runs at edge, Smart Placement has NO EFFECT
    const data = await this.env.DATABASE.prepare('SELECT * FROM users').all()
    return data
  }
}

export async function scheduled(event: ScheduledEvent, env: Env) {
  // NOT affected by Smart Placement
}

Consequence: If your backend logic uses RPC methods (WorkerEntrypoint), Smart Placement cannot optimize those calls. You must use fetch-based patterns for Smart Placement to work.

Solution: Convert RPC methods to fetch endpoints, or use a wrapper Worker with fetch handler that calls your backend RPC (though this adds latency).

Baseline Traffic

Smart Placement automatically routes 1% of requests WITHOUT optimization as baseline for performance comparison.

Validation Rules

Mutually exclusive fields:

• mode cannot be used with explicit placement fields (region, host, hostname)
• Choose either Smart Placement OR explicit placement, not both

// ✅ Valid - Smart Placement
{ "placement": { "mode": "smart" } }

// ✅ Valid - Explicit Placement (different feature)
{ "placement": { "region": "us-east1" } }

// ❌ Invalid - Cannot combine
{ "placement": { "mode": "smart", "region": "us-east1" } }

Dashboard Configuration

Workers & Pages → Select Worker → Settings → General → Placement: Smart → Wait 15min → Check Metrics

TypeScript Types

interface Env {
  BACKEND: Fetcher
  DATABASE: D1Database
}

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const data = await env.DATABASE.prepare('SELECT * FROM table').all()
    return Response.json(data)
  },
} satisfies ExportedHandler<Env>

Cloudflare Pages/Assets Warning

CRITICAL PERFORMANCE ISSUE: Enabling Smart Placement with assets.run_worker_first = true in Pages projects severely degrades asset serving performance. This is one of the most common misconfigurations.

Why this is bad:

• Smart Placement routes ALL requests (including static assets) away from edge to remote locations
• Static assets (HTML, CSS, JS, images) should ALWAYS be served from edge closest to user
• Result: 2-5x slower asset loading times, poor user experience

Problem: Smart Placement routes asset requests away from edge, but static assets should always be served from edge closest to user.

Solutions (in order of preference):

1. Recommended: Split into separate Workers (frontend at edge + backend with Smart Placement)
2. Set "mode": "off" to explicitly disable Smart Placement for Pages/Assets Workers
3. Use assets.run_worker_first = false (serves assets first, bypasses Worker for static content)

// ❌ BAD - Degrades asset performance by 2-5x
{
  "name": "pages-app",
  "placement": { "mode": "smart" },
  "assets": { "run_worker_first": true }
}

// ✅ GOOD - Frontend at edge, backend optimized
// frontend-worker/wrangler.jsonc
{
  "name": "frontend",
  "assets": { "run_worker_first": true }
  // No placement - runs at edge
}

// backend-worker/wrangler.jsonc
{
  "name": "backend-api",
  "placement": { "mode": "smart" },
  "d1_databases": [{ "binding": "DB", "database_id": "xxx" }]
}

Key takeaway: Never enable Smart Placement on Workers that serve static assets with run_worker_first = true.

Local Development

Smart Placement does NOT work in wrangler dev (local only). Test by deploying: wrangler deploy --env staging