@foladayo/sveltekit-adapter-lambda

AWS Lambda adapter for SvelteKit applications

Installation

npm install @foladayo/sveltekit-adapter-lambda

Usage

// svelte.config.js
import adapter from "@foladayo/sveltekit-adapter-lambda";

export default {
  kit: {
    adapter: adapter(),
  },
};

npm run build

The adapter generates a build/ directory with your Lambda function:

import { handler } from "./build/index.js";

Use index.handler as your Lambda function handler.

Configuration Options

// svelte.config.js
import adapter from "@foladayo/sveltekit-adapter-lambda";

export default {
  kit: {
    adapter: adapter({
      out: "build", // Output directory (default: 'build')
      precompress: false, // Gzip assets (default: false)
      binaryMediaTypes: ["image/*"], // Binary content types for base64 encoding
      bodySizeLimit: 6291456, // Body size limit in bytes (6MB default)
      envPrefix: "MY_APP_", // Environment variable prefix
      external: ["@aws-sdk/client-s3"], // Additional external dependencies
      serveStatic: false, // Serve static assets from Lambda (default: false)
    }),
  },
};

Static Asset Serving

By default, this adapter is optimized for SSR (Server-Side Rendering) only and does not serve static assets from Lambda.

Recommended Setup (Default)

adapter({
  serveStatic: false, // Default - Lambda handles SSR only
});

Use CloudFront + S3 to serve static assets for optimal performance and cost efficiency.

Lambda Static Serving (Optional)

adapter({
  serveStatic: true, // Serves static assets from Lambda with optimized caching
});

When enabled, the adapter uses @foladayo/web-file-server for high-performance static asset serving with:

• Compression Support: Brotli, Gzip, Deflate with precompressed file detection
• Smart Caching: Immutable assets get 1-year cache, regular assets get 1-hour cache
• Security Features: Path traversal protection, symlink blocking, sanitized headers
• Range Requests: Support for partial content delivery
• Conditional Requests: ETags and Last-Modified headers for cache validation

⚠️ Note: While optimized, serving static assets from Lambda still increases costs compared to CloudFront + S3. Use serveStatic: true for simple deployments or when you need centralized asset serving.

Lambda Handler

The generated handler function is located at build/index.handler and supports:

• API Gateway v1/v2 events
• Application Load Balancer events
• Lambda Function URLs events
• Automatic binary content detection and base64 encoding
• Multi-value headers and cookies
• Request validation with comprehensive error handling
• Response size protection (6MB Lambda limit enforcement)
• Security hardening with input sanitization

Accessing Lambda Context

// src/routes/+page.server.js
export async function load({ platform }) {
  const requestId = platform?.context?.awsRequestId;
  const timeRemaining = platform?.context?.getRemainingTimeInMillis();
  const event = platform?.event; // Original Lambda event

  return { requestId, timeRemaining };
}

Environment Variables

Environment variables are available through process.env. If you configure an envPrefix, the adapter will look for prefixed environment variables:

// With envPrefix: 'MY_APP_'
adapter({
  envPrefix: "MY_APP_",
});

// Environment: MY_APP_DATABASE_URL=postgres://...
// Access as: process.env.MY_APP_DATABASE_URL

Requirements

• Node.js: 22+ (LTS)
• SvelteKit: 2.0+
• AWS Lambda: nodejs22.x runtime