Using Boto S3 with overriding the actual connection endpoint, but not the apparent hostname.

boto_override_connection.py

# This how you can control where boto/requests are actually connecting to,
# while not otherwise mucking with ANY of the HTTP headers, which could invalidate AWS signatures
# The only DNS lookup that should be triggered by this is from the PATCH_new_conn function.
# No other DNS lookups should occur.
#
# For example, this allows you to configure a Ceph RGW instance to respond to the AWS hostname s3.amazonaws.com, 
# and then test it, without any modification of your local DNS.
#
# Copyright Robin Johnson 2016 <robin.johnson@dreamhost.com>

import requests.packages.urllib3.connection
import boto
import boto.s3.connection

class CustomHTTPConnection_requests(requests.packages.urllib3.connection.HTTPConnection):
    def __init__(self, *args, **kw):
        self.connect_host = kw.pop('connect_host', None)
        self.connect_port = kw.pop('connect_port', None)
        #print('Spawned %s forced via %s:%s' % (self.__class__, self.connect_host, self.connect_port))
        return super(CustomHTTPConnection_requests, self).__init__(*args, **kw)


class CustomHTTPSConnection_requests(requests.packages.urllib3.connection.HTTPSConnection):
    def __init__(self, *args, **kw):
        self.connect_host = kw.pop('connect_host', None)
        self.connect_port = kw.pop('connect_port', None)
        #print('Spawned %s forced via %s:%s' % (self.__class__, self.connect_host, self.connect_port))
        return super(CustomHTTPSConnection_requests, self).__init__(*args, **kw)

def PATCH_new_conn(self):
    """ Establish a socket connection, possibly to an overridden host/port.

    :return: a new socket connection
    """
    # resolve hostname to an ip address; use your own
    # resolver here, as otherwise the system resolver will be used.
    (host, port) = (self.host, self.port)
    if self.connect_host is not None:
       host = self.connect_host
    if self.connect_port is not None:
       port = self.connect_port
    try:
        conn = socket.create_connection(
            (host, port),
            self.timeout,
            self.source_address,
        )
    except (AttributeError, TypeError) as e: # Python 2.6
        conn = socket.create_connection(
            (host, port),
            self.timeout,
        )
    return conn

CustomHTTPConnection_requests._new_conn = PATCH_new_conn
CustomHTTPSConnection_requests._new_conn = PATCH_new_conn

# This is the "Factory" that boto.s3.connection.S3Connection expects.
def HTTPConnectionFactoryFactory(connect_host, connect_port, ssl=False):
    cls = CustomHTTPConnection_requests
    if ssl:
      cls = CustomHTTPSConnection_requests
    def f(*args, **kw):
        #print('Factory: Prepared %s forced via %s:%s' % (cls, connect_host, connect_port))
        (kw['connect_host'], kw['connect_port']) = (connect_host, connect_port)
        return cls(*args, **kw)
    return f
  
def __main__():
    connect_host = 'some-random-hostname'
    connect_port = 7480 # Ceph RGW directly!
    connect_ssl = False
    factory = HTTPConnectionFactoryFactory(connect_host, connect_port, ssl=connect_ssl)
    factory_arg = (factory, ()) # second tuple element is for error handling
    s3conn = boto.s3.connection.S3Connection('<aws access key>', '<aws secret key>', https_connection_factory=factory_arg)