Deleting Lambda function

We will create a Lambda function that deletes all items with the specified partition key and sort key in the DynamoDB table. It also deletes the corresponding image file from the S3 bucket.

Edit SAM Template

1. Open the template.yaml file in the fcaj-book-shop folder.

2. Add the following resource at the end of the file to create the BookDelete Lambda function:

   BookDelete:
     Type: AWS::Serverless::Function
     Properties:
       CodeUri: fcaj-book-shop/book_delete
       Handler: book_delete.lambda_handler
       Runtime: python3.13
       FunctionName: book_delete
       Environment:
         Variables:
           BUCKET_NAME: !Ref BookImageResizeShop
           TABLE_NAME: !Ref BooksTable
       Architectures:
         - x86_64
       Policies:
         - Statement:
             - Sid: VisualEditor0
               Effect: Allow
               Action:
                 - dynamodb:DeleteItem
                 - dynamodb:GetItem
                 - dynamodb:Query
                 - s3:DeleteObject
               Resource:
                 - !Sub arn:aws:dynamodb:${AWS::Region}:${AWS::AccountId}:table/${booksTableName}
                 - !Join
                   - ""
                   - - "arn:aws:s3:::"
                     - !Ref BookImageResizeShop
                     - /*
   

   

This resource defines a Lambda function named book_delete that:

• Uses Python 3.13 runtime on x86_64 architecture
• Has environment variables for BUCKET_NAME (pointing to the resize bucket) and TABLE_NAME
• Is granted dynamodb:DeleteItem, dynamodb:GetItem, dynamodb:Query permissions on the Books table
• Is granted s3:DeleteObject permission on the BookImageResizeShop bucket

Create Lambda Function Code

3. The directory structure is as follows:

   fcaj-book-shop
   ├── fcaj-book-shop
   │   ├── books_list
   │   │   └── books_list.py
   │   ├── book_create
   │   │   ├── book_create.py
   │   │   └── requirements.txt
   │   └── book_delete
   │       └── book_delete.py
   └── template.yaml
   

   • Create the book_delete folder in the fcaj-book-shop/fcaj-book-shop/ directory.
   • Create the book_delete.py file and copy the following code into it:

   import boto3
   import os
   
   BUCKET = os.environ['BUCKET_NAME']
   TABLE = os.environ['TABLE_NAME']
   
   s3_client = boto3.client('s3')
   dynamodb = boto3.resource('dynamodb')
   table = dynamodb.Table(TABLE)
   
   header_res = {
       "Content-Type": "application/json",
       "Access-Control-Allow-Origin": "*",
       "Access-Control-Allow-Methods": "OPTIONS,POST,GET,DELETE",
       "Access-Control-Allow-Headers": "Content-Type,X-Amz-Date,Authorization,X-Api-Key,X-Amz-Security-Token",
   }
   
   
   def lambda_handler(event, context):
       delete_id = event.get('pathParameters', {})
       delete_id['rv_id'] = 0
   
       try:
           # Get item from id
           try:
               delete_item = table.get_item(Key=delete_id)
               image_path = delete_item['Item'].get('image', '')
               image_name = image_path.split('/')[-1]
   
           except Exception as e:
               print(f"Error getting item with that {delete_id['id']}")
               raise Exception(f"Error getting item with that {delete_id['id']}")
   
           # Delete item in DynamoDB and s3 bucket
           try:
               items_with_same_id = table.query(
                   TableName=TABLE,
                   ProjectionExpression='rv_id',
                   KeyConditionExpression='id = :id',
                   ExpressionAttributeValues={':id': delete_id['id']}
               )
   
               for item in items_with_same_id['Items']:
                   delete_id['rv_id'] = item['rv_id']
                   table.delete_item(Key=delete_id)
   
               s3_client.delete_object(Bucket=BUCKET, Key=image_name)
   
           except Exception as e:
               print(f"Error getting item with that {delete_id['id']}")
               raise Exception(f"Error getting item with that {delete_id['id']}")
   
           return {
               'statusCode': 200,
               'body': 'Successfully delete item!',
               'headers': header_res
           }
   
       except Exception as e:
           print(f'Error deleting item: {e}')
           raise Exception(f'Error deleting item: {e}')
   

   

Build and Deploy

4. Run the following commands to build and validate the SAM template:

   sam validate
   sam build
   

   

5. Deploy the updated stack:

   sam deploy
   

   The changeset will show new resources being added:

   • BookDeleteRole (AWS::IAM::Role)
   • BookDelete (AWS::Lambda::Function)

   Enter y to confirm the deployment.

   

6. Wait for the deployment to complete. You should see Successfully created/updated stack.

   

Verify on AWS Console

7. Open the Lambda console. You should now see three functions: books_list, book_create, and book_delete.

   

8. Click on the book_delete function. Review the Code source section.

   

9. Review the Function overview section showing the function diagram.

   

10. Click the Configuration tab, then select Permissions from the left menu. Click on the execution role name (e.g., fcaj-book-shop-BookDeleteRole-...).

    

11. At the IAM Role page, check the Permissions policies section. You should see:

    • AWSLambdaBasicExecutionRole (AWS managed) - for CloudWatch Logs
    • BookDeleteRolePolicy0 (Customer inline) - the custom policy we defined

    

12. Click on BookDeleteRolePolicy0 to expand it. Review the policy JSON that grants dynamodb:DeleteItem, dynamodb:GetItem, dynamodb:Query, and s3:DeleteObject permissions.