prompter: What is the best design of a system that uploads a file to S3, than resizes it with lambda but using the same key as uploaded, without triggering the resize lambda function twice or more?

assistant: A possible solution to this problem is to use a S3 bucket event trigger to trigger the resizing Lambda function when a new file is uploaded to the S3 bucket. You can set the event to trigger the Lambda function only when a new object is created, not when it's modified. The Lambda function can then resize the file and store the resized version in the same S3 bucket using the same key as the original file, but with a different file format (e.g. adding "_resized" to the filename).

Additionally, you can add a check in the Lambda function to ensure it only resizes the file once. For example, you can store metadata in the object's metadata in S3 to indicate whether the file has been resized or not. Before resizing, the Lambda function can check this metadata and only resize the file if it hasn't been resized already.

By combining these two strategies, you can ensure that the Lambda function is triggered only once for each new file uploaded to the S3 bucket and that the resized version is stored in the same S3 bucket with the same key as the original file.

assistant: To prevent triggering the resize Lambda function multiple times, you can use a unique identifier in the object key and check if it exists before triggering the resize function.

Here's one possible design of a system that uploads a file to S3 and resizes it with a Lambda function:

The user uploads a file to S3, which triggers a S3 "Put" event.
The S3 event invokes a Lambda function (let's call it the "controller" function) that is responsible for processing the uploaded file.
The controller function generates a unique identifier (e.g., a timestamp) and appends it to the original file key.
The controller function checks if an object with the new key exists in S3.
If the object does not exist, the controller function triggers the resize Lambda function (let's call it the "resizer" function) with the new key as input.
The resizer function resizes the file and stores it in S3 under the new key.
If the object already exists, the controller function terminates and does not trigger the resizer function.
This design ensures that the resizer function is triggered only once per unique file, and that the resized file is stored under a unique key.

prompter: Show me how with AWS SAM CLI commands or as a bash script

assistant: Here's an example AWS SAM CLI command to create a SAM template for this setup:
sam init --runtime python3.8
cd sam-app/
sam build
sam package --output-template-file packaged.yaml
sam deploy --template-file packaged.yaml --stack-name s3-resize-stack --capabilities CAPABILITY_IAM

Here's the Sam template: 

---
AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Resources:
  S3Bucket:
    Type: AWS::S3::Bucket
    DeletionPolicy: Retain
    Properties:
      BucketName: my-resize-bucket
      NotificationConfiguration:
        LambdaConfigurations:
          - Event: s3:ObjectCreated:*
            Function: !GetAtt LambdaResizeFunction.Arn

  LambdaResizeFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: resize_function.py
      Handler: index.handler
      Runtime: python3.8
      Environment:
        Variables:
          S3_BUCKET: !Ref S3Bucket
      Policies:
        - S3CrudPolicy:
            BucketName: !Ref S3Bucket

And here's an example Python script for the Lambda function that resizes the uploaded file:

import boto3

def handler(event, context):
    s3 = boto3.client('s3')
    bucket_name = os.environ['S3_BUCKET']

    for record in event['Records']:
        file_key = record['s3']['object']['key']
        # resize the file using the boto3 library
        # save the resized file back to S3 with the same key
        s3.upload_file(resized_file, bucket_name, file_key)

This setup ensures that the Lambda function is triggered only once per new object uploaded and resizes the file using the same key.

assistant: Here's a bash script that implements the described system using the AWS CLI:

```
#!/bin/bash

# Define the S3 bucket and key of the uploaded file
bucket_name="your-s3-bucket"
object_key="path/to/your/uploaded/file.jpg"

# Check if the resized object already exists in the S3 bucket
resized_object_key="${object_key%.*}-resized.${object_key##*.}"
aws s3 ls "s3://$bucket_name/$resized_object_key" &> /dev/null
if [ $? -ne 0 ]; then
  # Resize the uploaded object and store the resized object in the S3 bucket
  # using the same key as the uploaded object but with a different file extension
  aws s3 cp "s3://$bucket_name/$object_key" - | \
    convert - -resize 800x800\> "s3://$bucket_name/$resized_object_key"
fi
```

This script assumes that you have the AWS CLI and the ImageMagick convert tool installed on your machine. You'll need to replace your-s3-bucket and path/to/your/uploaded/file.jpg with the actual names of your S3 bucket and uploaded file, respectively.

This script checks if the resized object already exists in the S3 bucket by using the aws s3 ls command and checking its exit code. If the resized object does not exist, the script uses the aws s3 cp command to copy the uploaded object from the S3 bucket to the standard output, pipes it through the ImageMagick convert tool to resize the image, and finally uses the aws s3 cp command to store the resized object in the S3 bucket using the same key as the uploaded object but with a different file extension.

assistant: Here's one possible design for a system that uploads a file to S3 and resizes it using AWS Lambda, without triggering the resize Lambda function multiple times:

The user uploads a file to an S3 bucket.
S3 generates a "Put Object" event and triggers a Lambda function.
The Lambda function checks if the uploaded file has already been resized by checking if the resized file exists in the same S3 bucket with the same key but a different file extension (e.g. ".resized").
If the resized file exists, the Lambda function returns without doing anything further.
If the resized file does not exist, the Lambda function reads the original file from S3, performs the resize operation, and writes the resized file back to S3 with the same key but with a different file extension.
The Lambda function updates the metadata of the original file in S3 with a flag indicating that the file has been resized.
This design ensures that the Lambda function is only triggered once for each uploaded file, and that the resized file is stored in the same S3 bucket with the same key as the original file, making it easier to keep track of the resized files.

prompter: Suggest an alternative approach that keeps the original filenames.