Upload Images to AWS S3 using Node.js and Multer

Uploading images to AWS S3 from a Node.js server is a common requirement in many web applications — whether it's profile pictures, product images, or documents.

In this guide, you'll learn how to use Express, Multer, and the AWS SDK v3 to handle file uploads and store them directly into your S3 bucket.

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Step 1: Setup AWS S3 Bucket & IAM

1. Go to AWS S3 Console.
2. Create a new bucket (e.g. my-app-uploads) and make it private.
3. Go to IAM → Create a user with Programmatic Access.
4. Attach the policy AmazonS3FullAccess to that user.
5. Note the Access Key ID and Secret Access Key.

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Step 2: Create .env File

Now, add your AWS credentials and bucket details to a .env file:

// .env
AWS_REGION=your-region
AWS_ACCESS_KEY_ID=your-access-key
AWS_SECRET_ACCESS_KEY=your-secret-key
AWS_BUCKET_NAME=your-bucket-name
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Step 3: Setup Project & Install Dependencies

mkdir s3-uploader && cd s3-uploader
npm init -y

npm install express multer dotenv @aws-sdk/client-s3
npm install -D typescript ts-node @types/node @types/express
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Step 4: Setup Express Server

// index.ts
import express from "express";
import dotenv from "dotenv";
import uploadRoute from "./routes/upload";

dotenv.config();

const app = express();
app.use("/api", uploadRoute);

const PORT = process.env.PORT || 8081;
app.listen(PORT, () => {
  console.log(`🚀 Server running on http://localhost:${PORT}`);
});
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Step 5: Configure Multer for File Uploads

To handle file uploads in Node.js, we use the multer middleware.

There are two strategies:

✅ DiskStorage – Best for large files

// utils/multer.ts
import multer from "multer";
import { randomUUID } from "crypto";

const upload = multer({
  storage: multer.diskStorage({
    destination: "./tmp", // or use os.tmpdir() for system temp directory
    filename: (req, file, cb) => {
      const uniqueName = `${Date.now()}-${randomUUID()}-${file.originalname}`;
      cb(null, uniqueName);
    },
  }),
});

export default upload;
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⚠️ MemoryStorage – For small files (under 1MB)

const upload = multer({ storage: multer.memoryStorage() });
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⚠️ Avoid using memory storage for large files — it will be stored in RAM and may crash the server.

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Step 6: Configure AWS SDK (S3 Client)

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


if (!process.env.AWS_ACCESS_KEY_ID || !process.env.AWS_SECRET_ACCESS_KEY || !process.env.AWS_REGION) 
    throw new Error("AWS keys are misssing");

export const s3 = new S3Client({
  region: process.env.AWS_REGION,
  credentials: {
    accessKeyId: process.env.AWS_ACCESS_KEY_ID,
    secretAccessKey: process.env.AWS_SECRET_ACCESS_KEY,
  },
});
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Step 7: Create Upload Route

// routes/upload.ts
import express from "express";
import fs from "fs";
import { PutObjectCommand } from "@aws-sdk/client-s3";
import upload from "../utils/multer";
import { s3 } from "../lib/s3";

const router = express.Router();

router.post("/upload", upload.single("file"), async (req, res) => {
  const file = req.file;
  if (!file) return res.status(400).json({ error: "No file uploaded" });

  const fileStream = fs.createReadStream(file.path);

  const uploadParams = {
    Bucket: process.env.AWS_BUCKET_NAME!,
    Key: `uploads/${file.filename}`,
    Body: fileStream,
    ContentType: file.mimetype,
  };

  try {
    await s3.send(new PutObjectCommand(uploadParams));
    fs.unlinkSync(file.path); // Clean up local file
    res.status(200).json({ message: "Upload successful" });
  } catch (err) {
    fs.unlinkSync(file.path); // Clean up local file on error
    res.status(500).json({ error: "Upload failed", details: err });
  }
});

export default router;
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Final Notes

• ✅ Always clean up your temp directory after uploading or if the upload fails.
• ✅ Your IAM user must have s3:PutObject permissions.
• ✅ Handle file size limits and allowed mimetypes for production.

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You now have a complete and secure Node.js file upload system using:

• Express + Multer
• AWS SDK v3
• S3 as your file storage

Perfect for avatars, media uploads, document storage, and more.