Setting up S3 and CRUD API

Content:

Create S3 bucket

  1. Go to the S3 Console.
  2. Click Create bucket.
  3. Name it.
  4. Choose a region, for example: (ap-southeast-1).
  5. Leave the rest of the settings as default.
  6. Click Create bucket to finish setup.

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Prepare sample quiz JSON

  1. On your local machine, create a file named (quiz.json) with the following content, and upload that file to newly created bucket.

{ 
  "id": "quiz-001",
  "title": "AWS Basics Quiz",
  "questions": [
    {
      "id": "q1",
      "text": "Which AWS services are serverless?",
      "type": "multiple", 
      "options": ["EC2", "S3", "Lambda", "Fargate"],
      "answer": [1, 2, 3]
    },
    {
      "id": "q2",
      "text": "What is the max size of an S3 object?",
      "type": "single",
      "options": ["5 GB", "50 GB", "5 TB", "50 TB"],
      "answer": [2]
    }
  ]
}

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Create IAM role and policy

  1. Go to the IAM Console.
  2. Select Policies → Create Policy.
  3. We will create 3 separate policies: alt text
  4. Choose the JSON tab and paste the following:

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  • For s3ReadOnlyAccess:
{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": "s3:GetObject",
            "Resource": "arn:aws:s3:::myprojectbucket1290/*"
        }
    ]
}
  • For s3PutOnlyAccess:
{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": "s3:PutObject",
            "Resource": "arn:aws:s3:::myprojectbucket1290/*"
        }
    ]
}
  • For s3RemoveOnlyAccess:
{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": "s3:DeleteObject",
            "Resource": "arn:aws:s3:::myprojectbucket1290/*"
        }
    ]
}

  1. Name the policy and create it.

  2. Now go to Roles → Create Role. Each policy will have their own role

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  1. Select Lambda as the trusted entity type.

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  1. Attach the policy you just created.

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  1. Name the role and create it.

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  1. Repeat the steps for s3PutOnlyAccess and s3RemoveOnlyAccess
  2. Final result: alt text alt text alt text

Create Lambda functions

Create 4 Lambda functions using Node.js 20.x or 22.x. Use the following names and HTTP methods:

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Add Lambda code

Example: myGetFunction


import { S3Client, GetObjectCommand } from "@aws-sdk/client-s3";
import { Readable } from "stream";

const s3 = new S3Client({});
const BUCKET = "myprojectbucket1290"; //Change bucket name here

const streamToString = (stream) =>
  new Promise((resolve, reject) => {
    const chunks = [];
    stream.on("data", (chunk) => chunks.push(chunk));
    stream.on("error", reject);
    stream.on("end", () => resolve(Buffer.concat(chunks).toString("utf-8")));
  });

export const handler = async (event) => {
  const key = event.queryStringParameters?.key || "quiz.json";
  console.log("🔍 GET request for key:", key);

  try {
    const res = await s3.send(new GetObjectCommand({ Bucket: BUCKET, Key: key }));
    const data = await streamToString(res.Body);
    console.log(" Successfully retrieved:", key);
    return {
      statusCode: 200,
      body: data,
      headers: { "Content-Type": "application/json" }
    };
  } catch (err) {
    console.error(" Error reading object:", err);
    return { statusCode: 500, body: JSON.stringify({ error: err.message }) };
  }
};

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Repeat similarly for POST (create), PUT (update), and DELETE. Use the code below:

Example: myPostFunction

import { S3Client, PutObjectCommand } from "@aws-sdk/client-s3";
const s3 = new S3Client({});
const BUCKET = "myprojectbucket1290";

export const handler = async (event) => {
  const body = JSON.parse(event.body || "{}");
  const key = body.key || "quiz.json";
  const data = body.data;

  console.log(" POST request:", { key, data });

  if (!data) {
    console.warn(" Missing 'data' in request");
    return { statusCode: 400, body: "Missing 'data' in request body" };
  }

  try {
    await s3.send(new PutObjectCommand({
      Bucket: BUCKET,
      Key: key,
      Body: JSON.stringify(data),
      ContentType: "application/json"
    }));
    console.log(" Created quiz:", key);
    return { statusCode: 200, body: `Created quiz: ${key}` };
  } catch (err) {
    console.error(" Error creating object:", err);
    return { statusCode: 500, body: JSON.stringify({ error: err.message }) };
  }
};

Example: myPutFunction

import { S3Client, PutObjectCommand } from "@aws-sdk/client-s3";
const s3 = new S3Client({});
const BUCKET = "myprojectbucket1290";

export const handler = async (event) => {
  const key = event.queryStringParameters?.key || "quiz.json";
  const body = JSON.parse(event.body || "{}");
  const data = body.data;

  console.log(" PUT request to update:", { key, data });

  if (!data) {
    console.warn(" Missing 'data' in request");
    return { statusCode: 400, body: "Missing 'data' in request body" };
  }

  try {
    await s3.send(new PutObjectCommand({
      Bucket: BUCKET,
      Key: key,
      Body: JSON.stringify(data),
      ContentType: "application/json"
    }));
    console.log(" Updated quiz:", key);
    return { statusCode: 200, body: `Updated quiz: ${key}` };
  } catch (err) {
    console.error("❌ Error updating object:", err);
    return { statusCode: 500, body: JSON.stringify({ error: err.message }) };
  }
};

Example: myDeleteFunction

import { S3Client, DeleteObjectCommand } from "@aws-sdk/client-s3";
const s3 = new S3Client({});
const BUCKET = "myprojectbucket1290";

export const handler = async (event) => {
  const key = event.queryStringParameters?.key || "quiz.json";
  console.log(" DELETE request for:", key);

  try {
    await s3.send(new DeleteObjectCommand({ Bucket: BUCKET, Key: key }));
    console.log(" Deleted quiz:", key);
    return { statusCode: 200, body: `Deleted quiz: ${key}` };
  } catch (err) {
    console.error(" Error deleting object:", err);
    return { statusCode: 500, body: JSON.stringify({ error: err.message }) };
  }
};

Testing

Test all functions to confirm they’re working properly.

myGetFunction alt text

myPostFunction

  • for Post and Put functions, use this as request body:
{
  "key": "quiz-aws.json",
  "data": { "id": "quiz-aws", "title": "AWS Quiz", "questions": [] }
}

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myPutFunction alt text

myDeleteFunction

  • For Delete function, use this in body:
{
  "queryStringParameters": {
    "key": "quiz-aws.json"
  }
}

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Configure API Gateway

  1. Go to the API Gateway Console.
  2. Create a new HTTP API, name it QuizAPI.
  3. Add created Lambda functions as intergration

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  1. Add the following routes and map them to their corresponding Lambda functions:

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  1. Deploy to a default stage with auto-deploy on

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Final result:

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###5. Test with Postman

  • From API Gateway dashboard, choose your api gateway alt text

  • Next, click on your api gateway name to view the detail alt text

  • Copy the invoke URL and open postman for testing: alt text

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Outcome

You now have a complete CRUD-capable quiz API backed by:

  • (S3) for JSON file storage
  • (Lambda) for serverless execution logic
  • (API Gateway) for HTTP interface
  • (JSON) as the quiz file format

This setup forms the foundation of your serverless, event-driven learning platform.