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()

Solution

"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.

---

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.