Lambda Image Resizer

A serverless AWS Lambda function that automatically resizes images uploaded to an S3 bucket using the sharp image processing library.

Features

• ✅ Resizes images to specified dimensions
• ☁️ Triggered by S3 upload events
• 🧠 Uses the sharp library for fast processing
• 🪶 Stores the resized image in a target S3 bucket

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📦 Setup Instructions

1. Clone the Repo

git clone https://github.com/dlauck92/lambda-image-resizer.git
cd lambda-image-resizer

2. Install Dependencies

npm install

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☁️ AWS Configuration

Step 1: Create IAM Policy

Create a policy that allows access to the source and destination S3 buckets.

Example Policy (resize-image-s3-policy.json)

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "s3:GetObject",
        "s3:PutObject"
      ],
      "Resource": [
        "arn:aws:s3:::YOUR_SOURCE_BUCKET_NAME/*",
        "arn:aws:s3:::YOUR_DEST_BUCKET_NAME/*"
      ]
    },
    {
      "Effect": "Allow",
      "Action": [
        "logs:CreateLogGroup",
        "logs:CreateLogStream",
        "logs:PutLogEvents"
      ],
      "Resource": "*"
    }
  ]
}

Create the Policy

aws iam create-policy \
  --policy-name ResizeImageS3Policy \
  --policy-document file://resize-image-s3-policy.json

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Step 2: Create IAM Role for Lambda

Create a trust policy for Lambda:

Trust Policy (trust-policy.json)

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "Service": "lambda.amazonaws.com"
      },
      "Action": "sts:AssumeRole"
    }
  ]
}

Create the Role

aws iam create-role \
  --role-name LambdaImageResizerRole \
  --assume-role-policy-document file://trust-policy.json

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Step 3: Attach Policy to Role

aws iam attach-role-policy \
  --role-name LambdaImageResizerRole \
  --policy-arn arn:aws:iam::YOUR_ACCOUNT_ID:policy/ResizeImageS3Policy

Replace YOUR_ACCOUNT_ID with your actual AWS account ID.

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Step 4: Create the Lambda Function

Package the Function

zip -r function.zip .

Create the Lambda Function

aws lambda create-function \
  --function-name image-resizer \
  --runtime nodejs18.x \
  --role arn:aws:iam::YOUR_ACCOUNT_ID:role/LambdaImageResizerRole \
  --handler index.handler \
  --timeout 10 \
  --memory-size 512 \
  --zip-file fileb://function.zip \
  --environment Variables="{DEST_BUCKET=your-destination-bucket,MAX_WIDTH=800,MAX_HEIGHT=800}"

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Step 5: Set Up S3 Trigger

1. Go to the S3 Console, select your source bucket.
2. Go to Properties > Event Notifications.
3. Create a new event:
   • Event Name: image-upload
   • Event Type: PUT
   • Prefix: (optional, e.g., uploads/)
   • Destination: Lambda Function → image-resizer

Make sure Lambda has permission to be invoked by S3. AWS usually prompts for this automatically.

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🧪 Testing

Upload an image to your source S3 bucket:

aws s3 cp ./example.jpg s3://your-source-bucket/uploads/

The resized image will appear in your destination bucket.

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🧾 License

MIT License © Drew Lauck