Upload Files to Amazon S3 Using Node.js, Express, and AWS SDK v3

Amit Kumar — Sun, 12 Jul 2026 19:43:04 +0000

Uploading files is a feature you'll eventually need in almost every web application—whether it's profile pictures, PDFs, invoices, or media files. Instead of storing uploads on your server, Amazon S3 provides a reliable, scalable, and highly durable solution.

In this tutorial, we'll build a simple REST API using Node.js, Express, Multer, and AWS SDK v3 that uploads files directly to an Amazon S3 bucket.

Prerequisites

Before you begin, make sure you have:

Node.js 18 or later
An AWS account
An Amazon S3 bucket
An IAM user with programmatic access
AWS Access Key ID and Secret Access Key

Step 1: Create a New Project

mkdir s3-upload-api
cd s3-upload-api

npm init -y

Install the required packages:

npm install express multer dotenv uuid @aws-sdk/client-s3

Step 2: Configure Environment Variables

Create a .env file.

AWS_REGION=ap-south-1
AWS_ACCESS_KEY_ID=YOUR_ACCESS_KEY
AWS_SECRET_ACCESS_KEY=YOUR_SECRET_KEY
AWS_BUCKET_NAME=YOUR_BUCKET_NAME
PORT=3000

Create a .gitignore file.

node_modules
.env

Step 3: Configure the Amazon S3 Client

import { S3Client } from "@aws-sdk/client-s3";

const s3 = new S3Client({
  region: process.env.AWS_REGION,
  credentials: {
    accessKeyId: process.env.AWS_ACCESS_KEY_ID,
    secretAccessKey: process.env.AWS_SECRET_ACCESS_KEY,
  },
});

Step 4: Configure Multer

We'll use memory storage so files are uploaded directly to Amazon S3.

import multer from "multer";

const upload = multer({
  storage: multer.memoryStorage(),
});

Step 5: Create the Upload Endpoint

import { PutObjectCommand } from "@aws-sdk/client-s3";
import { v4 as uuid } from "uuid";

app.post("/upload", upload.single("file"), async (req, res) => {
  try {
    const filename = `${uuid()}-${req.file.originalname}`;

    await s3.send(
      new PutObjectCommand({
        Bucket: process.env.AWS_BUCKET_NAME,
        Key: filename,
        Body: req.file.buffer,
        ContentType: req.file.mimetype,
      })
    );

    res.json({
      success: true,
      filename,
    });
  } catch (error) {
    console.error(error);

    res.status(500).json({
      success: false,
      message: "Upload failed",
    });
  }
});

Step 6: Start the Server

npm start

Step 7: Test with Postman

Send a POST request to:

POST http://localhost:3000/upload

Select:

Body → form-data

Key: file
Type: File

Choose any image or document and click Send.

Example response:

{
  "success": true,
  "filename": "4c6ddcf2-profile.png"
}

You should now see the uploaded file in your Amazon S3 bucket.

Common Errors

AccessDenied

Your IAM user doesn't have permission to upload objects. Make sure the user has the s3:PutObject permission.

NoSuchBucket

Verify the bucket name and AWS Region.

InvalidAccessKeyId

Check that your AWS credentials are correct.

Next Steps

Once the basic upload API is working, you can enhance it by:

Supporting multiple file uploads
Generating pre-signed URLs
Validating file type and size
Uploading directly from a React application
Using CloudFront for faster content delivery
Organizing uploads into folders

Conclusion

Building a file upload API with Node.js and Amazon S3 is straightforward once you understand the basic workflow. Using Express, Multer, and the AWS SDK v3, you can create a scalable upload service in just a few steps. From here, you can add authentication, pre-signed URLs, image processing, or integrate the API into your frontend application.

If you've implemented file uploads differently or have tips for improving this approach, feel free to share them in the comments.

DEV Community: Amit Kumar