lambdaProject

Project: AWS Lambda + S3 Zipper (Ohio region - us-east-2)

Objective:
Trigger a Lambda function when a file is uploaded to an S3 bucket. The function compresses the file and uploads it to another bucket.

Step 1: Prepare Buckets

Go to the AWS S3 Console.
Create two buckets:
- Source bucket: my-first-test-bucket-aisalkyn
- Destination bucket: test-bucket-for-devopsstudents2

Step 2: Create IAM Role for Lambda

Go to the IAM Console.
Click "Create Role".
Choose "AWS service" and select "Lambda".
Click "Next".
Click "Create policy" to add the inline policy below.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "AllowReadFromSourceBucket",
      "Effect": "Allow",
      "Action": ["s3:GetObject"],
      "Resource": "arn:aws:s3:::my-first-test-bucket-aisalkyn/*"
    },
    {
      "Sid": "AllowWriteToDestBucket",
      "Effect": "Allow",
      "Action": ["s3:PutObject"],
      "Resource": "arn:aws:s3:::test-bucket-for-devopsstudents2/*"
    }
  ]
}

Attach the policy to the role.
Name the role lambda-log-s3-role.
Finish creating the role.

Step 3: Write the Lambda Function
Create a file named lambda_function.py with the following content:

import boto3
import zipfile
import io
import os

s3 = boto3.client('s3')

def lambda_handler(event, context):
    source_bucket = event['Records'][0]['s3']['bucket']['name']
    source_key = event['Records'][0]['s3']['object']['key']
    destination_bucket = os.environ['DEST_BUCKET']

    print(f"Zipping {source_key} from {source_bucket}...")

    file_obj = s3.get_object(Bucket=source_bucket, Key=source_key)
    file_content = file_obj['Body'].read()

    zip_buffer = io.BytesIO()
    with zipfile.ZipFile(zip_buffer, 'a', zipfile.ZIP_DEFLATED) as zip_file:
        zip_file.writestr(source_key, file_content)

    zip_buffer.seek(0)
    zipped_key = source_key + '.zip'
    s3.upload_fileobj(zip_buffer, destination_bucket, zipped_key)

    print(f"Uploaded zipped file as {zipped_key} to {destination_bucket}")

    return {
        'statusCode': 200,
        'body': f"Zipped and uploaded {zipped_key}"
    }

Step 4: Zip the Code

Open a terminal.
Navigate to the folder containing lambda_function.py.
Run:

zip function.zip lambda_function.py

Step 5: Deploy Lambda
Replace YOUR_ACCOUNT_ID with your actual AWS account ID.

aws lambda create-function \
  --function-name log-s3-upload \
  --runtime python3.12 \
  --role arn:aws:iam::YOUR_ACCOUNT_ID:role/lambda-log-s3-role \
  --handler lambda_function.lambda_handler \
  --zip-file fileb://function.zip \
  --environment Variables={DEST_BUCKET=test-bucket-for-devopsstudents2} \
  --region us-east-2

Step 6: Add S3 Trigger to Lambda

Go to Lambda Console.
Select log-s3-upload.
Go to Configuration > Triggers.
Click "Add trigger".
Select "S3", choose my-first-test-bucket-aisalkyn, and enable "All object create events".
Save.

Step 7: Upload Test File to S3

echo "This is a test file from Lambda demo" > test.txt
aws s3 cp test.txt s3://my-first-test-bucket-aisalkyn/

Step 8: Verify Lambda Execution in CloudWatch

Go to AWS Console > CloudWatch > Log groups.
Select /aws/lambda/log-s3-upload.
Click the latest log stream.
Check for output confirming successful zip and upload.

Step 9: Generate Pre-signed URL (optional)

aws s3 presign s3://test-bucket-for-devopsstudents2/test.txt.zip --region us-east-2

Open the returned URL in a browser to download the zipped file.

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