Package the Lambda function

Function Code

1. On your local machine:

• Create a new directory, I’ll name it workshop1, you can choose any name you want.

• Inside the directory create a Python file and name it lambda_function.py for our function.

• Copy the code below and paste it inside the file you’ve just created:

  from PIL import Image, ImageDraw, ImageFont
  import boto3
  import os
  
  s3 = boto3.client('s3')
  
  def add_text_watermark(image_path):
      watermark_text = "SAMPLE"
      image = Image.open(image_path)
      draw = ImageDraw.Draw(image)
  
      w, h = image.size
      x, y = int(w / 2), int(h / 2)
  
      font = ImageFont.load_default(size=30)
  
      draw.text((x, y), watermark_text, fill=(255, 255, 255), font=font, anchor='ms')
  
      image.save(image_path)
      image.close()
  
  def lambda_handler(event, context):
      # Extract the bucket name and key from the event
      bucket = event['Records'][0]['s3']['bucket']['name']
      key = event['Records'][0]['s3']['object']['key']
  
      # Define the download path in the Lambda temporary directory and the upload path
      download_path = '/tmp/' + os.path.basename(key)
      upload_key = 'destination/' + os.path.basename(key)  # Save watermarked images in 'destination' folder
  
      # Download the image from the 'source' folder
      source_key = 'source/' + os.path.basename(key)
      s3.download_file(bucket, source_key, download_path)
  
      # Add a watermark to the image
      add_text_watermark(download_path)
  
      # Upload the watermarked image to the 'destination' folder
      s3.upload_file(download_path, bucket, upload_key)
  
      # Clean up the temporary file
      os.remove(download_path)
  
      return {
          'statusCode': 200,
          'body': 'Watermark added successfully!'
      }
  

• This add_text_watermark function is a simple function using PIL that adds a white text watermark “SAMPLE” into the image and returns it.

• In general, the Lambda function will extract the event key and download the image with the “source/” prefix every time the user uploads an image object with this prefix in the S3 bucket. Then it will call the add_text_watermark function to add a watermark and then replace the source/ prefix with the destination/ prefix to add the edited image to the bucket.

2. We will need to install PIL inside the directory so that the function can call methods in the library.

• Inside the same directory of your lambda_function.py , run the command pip install -t . pillow. Pip will collect the pillow library inside the current directory, your directory now should look something like this:

• Now compress the directory into a single zip file by running the command zip -r ./my_package.zip . whereas my_package is the name of your .zip file that we’ll be uploaded to our lambda function

3. After you got the .zip package ready on your machine, go back to the Lambda console

• Click on the new Lambda function on the list we’ve just created.
• Click on Upload from then .zip file and select the my_package.zip file from your machine, wait for it to upload successfully and we will move on and test the function in the next step.