python - Transfer file from AWS S3 to SFTP using Boto 3

Question

I am a beginner in using Boto3 and I would like to transfer a file from an S3 bucket to am SFTP server directly.

My final goal is to write a Python script for AWS Glue.

I have found some article which shows how to transfer a file from an SFTP to an S3 bucket:
https://medium.com/better-programming/transfer-file-from-ftp-server-to-a-s3-bucket-using-python-7f9e51f44e35

Unfortunately I can't find anything which does the opposite action. Do you have any suggestions/ideas?

---

My first wrong attempt is below.

But I would like to avoid downloading while file to my local memory in order to move it then to SFTP.

import pysftp
import boto3

# get clients
s3_gl = boto3.client('s3', aws_access_key_id='', aws_secret_access_key='')

# parameters
bucket_gl = ''
gl_data = ''
gl_script = ''

source_response = s3_gl.get_object(Bucket=bucket_gl,Key=gl_script+'file.csv')
print(source_response['Body'].read().decode('utf-8'))

#---------------------------------

srv = pysftp.Connection(host="", username="", password="")

with srv.cd('relevant folder in sftp'): 
    srv.put(source_response['Body'].read().decode('utf-8')) 

# Closes the connection
srv.close()

Answer 1

"transfer ... directly" can mean number of different things.

Let's assume that you want to transfer the file via the local machine (where the Python code runs), without actually storing a temporary copy of the file to the local file system.

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For SFTP upload, you can use Paramiko library.

Assuming you already have your Paramiko SFTPClient (sftp) and Boto 3 client (s3) instances ready (what is covered in the article you have linked in your question), you can simply "glue" them together using file-like objects:

with sftp.open('/sftp/path/filename', 'wb', 32768) as f:
    s3.download_fileobj('mybucket', 'mykey', f)

For the purpose of the 32768 argument, see Writing to a file on SFTP server opened using pysftp "open" method is slow.