Serverless File Processing: Resize Images Automatically Using Lambda + S3

Handling images at scale can be challenging. Whether it's for a website, app, or storage optimization, resizing images automatically saves time and reduces storage costs.

With AWS Lambda and S3, you can build a fully serverless workflow that resizes images automatically whenever a new file is uploaded.

How It Works

The workflow is simple:

This approach requires no servers, scales automatically, and integrates seamlessly with your AWS environment.

AWS Services Used

Lambda Function Code (Node.js)

import { S3Client, GetObjectCommand, PutObjectCommand } from "@aws-sdk/client-s3"
import sharp from "sharp"

const s3 = new S3Client({ region: "us-east-1" })

export const handler = async (event) => {
  for (const record of event.Records) {
    const bucket = record.s3.bucket.name
    const key = record.s3.object.key

    // Get the original image
    const original = await s3.send(
      new GetObjectCommand({ Bucket: bucket, Key: key })
    )

    const buffer = await streamToBuffer(original.Body)

    // Resize the image
    const resized = await sharp(buffer)
      .resize({ width: 300 }) // Resize width to 300px
      .toBuffer()

    // Save resized image to another folder
    await s3.send(
      new PutObjectCommand({
        Bucket: bucket,
        Key: 'resized/${key}',
        Body: resized,
        ContentType: "image/jpeg"
      })
    )

    console.log('Resized image saved: resized/${key}')
  }
}

// Helper function to convert stream to buffer
const streamToBuffer = async (stream) => {
  const chunks = []
  for await (const chunk of stream) {
    chunks.push(chunk)
  }
  return Buffer.concat(chunks)
}

Setting Up S3 Event Trigger

Now, whenever you upload an image to 'uploads/', Lambda will automatically resize it and save it in 'resized/'.

Benefits of This Serverless Approach

Extending This Workflow

Final Thoughts

Serverless file processing with Lambda + S3 is a powerful pattern for modern applications. It reduces operational overhead, is cost-efficient, and can be extended to handle videos, PDFs, or any other files.

Start small with image resizing and expand your serverless workflows as your application grows. 🚀