Serverless is amazing when you don’t know what your server load will be and you pay only when your function runs.

More details on serverless here:

The Problem

Although it’s popular and used widely there are always some pros and cons.

One such con is API Gateway has a hard timeout of 30seconds. So, your API must return a response within 30 seconds, or else it’s going to fail.

What If you are creating an API to upload a file of maybe 30MB to AWS S3 using API Gateway?

There’s a high chance it will take a bit more than 30seconds and your API will eventually fail.

So, what’s the solution then? 🤔

We can use AWS S3 presigned URL to upload files to S3 without the hard time limit of 30seconds.

The Solution – Creating a simple AWS Lambda API to create presigned URLs for uploading.

Architecture

There’s already a blog post to show how to create a serverless API using AWS console which can be found below:

The serverless JavaScript code to create presigned URLs:

const AWS = require('aws-sdk');
const s3 = new AWS.S3({
  signatureVersion: 'v4'
});
const bucketName = process.env.S3_BUCKET_NAME; 
exports.handler = async (event, context, callback) => {
    const expiryInSeconds= 60 * 5;
    const body = JSON.parse(event.body);
    const key = 'files' + '/' + body['file_name'];
    
    const url = s3.getSignedUrl('putObject', {
        Bucket: bucketName,
        Key: key,
        Expires: expiryInSeconds,
    });
  
    const response = {
        statusCode: 200,
        headers: {
          'Access-Control-Allow-Origin': '*',
          'Access-Control-Allow-Credentials': true,
        },
        body: JSON.stringify({ filename: body['file_name'],  presigned_url: url}),
    };

    callback(null, response);
};

Here, we create an instance of AWS S3 and use a simple method called getSignedUrl() to generate resigned URLs.

On connecting it to API Gateway, we send a POST API call with the body having file_name as key.

Let’s see the deployed API in action

We pass file_name as car.jpg which creates a presigned_url for us to use.

Next, we copy the resigned URL and perform a PUT call as below:

We select the file(car.jpg) as binary and send a PUT request which response with 200 on success.

Now let us check s3 if the file is created:

So, we were successfully able to create a photo upload API with serverless 👌

Hope you liked it. Cheers 🍻