How to upload file from local machine to an EC2 instance? (Planning to use AWS SDK via Python)

Hello.

You cannot directly upload files to EC2 with the AWS SDK.
One way is to use an S3 event trigger to run Lambda and have it execute a Systems Manager RunCommand.
The Lambda code looks like this:

from datetime import datetime
import boto3
import os

ssm = boto3.client('ssm')

instance_id = os.environ['instance_id']
now = datetime.now()
file_name = 'file_name' + now.strftime('%Y%m%d%H%M%S')

def lambda_handler(event, context):
    bucket = event['Records'][0]['s3']['bucket']['name']
    key = event['Records'][0]['s3']['object']['key']
    response = ssm.send_command(
        InstanceIds=[instance_id],
        DocumentName='AWS-RunShellScript',
        Parameters={
            'commands': [
                f'aws s3 cp s3://{bucket}/{key} /home/ec2-user/{file_name}'
            ],
            'executionTimeout': ['3600'],
        }
    )