Impossible to create a bucket in us-east-1 if underlying botocore session sets another default region

[ChristianWeymannTNG]

Describe the bug

When creating an S3 client with region_name=us-east-1 from a boto3.Session, if the underlying botocore.session.Session is setup with a botocore.config.Config that defines a different region_name, creating buckets will always fail with an IllegalLocationConstraintException

Expected Behavior

Being able to create buckets in the us-east-1 region

Current Behavior

Traceback (most recent call last):
  File "scratch_20.py", line 14, in <module>
    client.create_bucket(Bucket="test-bucket-creation-20221111")
  File "site-packages/botocore/client.py", line 495, in _api_call
    return self._make_api_call(operation_name, kwargs)
  File "site-packages/botocore/client.py", line 914, in _make_api_call
    raise error_class(parsed_response, operation_name)
botocore.exceptions.ClientError: An error occurred (IllegalLocationConstraintException) when calling the CreateBucket operation: The unspecified location constraint is incompatible for the region specific endpoint this request was sent to.

Traceback (most recent call last):
  File "scratch_20.py", line 14, in <module>
    client.create_bucket(Bucket="test-bucket-creation-20221111", CreateBucketConfiguration={"LocationConstraint": "us-east-1"})
  File "site-packages/botocore/client.py", line 495, in _api_call
    return self._make_api_call(operation_name, kwargs)
  File "site-packages/botocore/client.py", line 914, in _make_api_call
    raise error_class(parsed_response, operation_name)
botocore.exceptions.ClientError: An error occurred (IllegalLocationConstraintException) when calling the CreateBucket operation: The us-east-1 location constraint is incompatible for the region specific endpoint this request was sent to.

Reproduction Steps

import boto3
from botocore.config import Config
from botocore.session import Session

config = Config(region_name="eu-west-1")
session = Session()
session.set_default_client_config(config)
boto_session = boto3.Session(botocore_session=session)

client = boto_session.client("s3", region_name="us-east-1")
client.create_bucket(Bucket="test-bucket-creation-20221111") #raises
client.create_bucket(Bucket="test-bucket-creation-20221111", CreateBucketConfiguration={"LocationConstraint": "us-east-1"}) #raises

client = boto_session.client("s3", region_name="ap-southeast-1")
client.create_bucket(Bucket="test-bucket-creation-20221111", CreateBucketConfiguration={"LocationConstraint": "ap-southeast-1"}) #works as expected

Possible Solution

In the example above, it seems like like for the specific case of "us-east-1", the S3 endpoint for "eu-west-1" is still called.

Additional Information/Context

No response

SDK version used

boto3 1.26.1, botocore 1.29.1

Environment details (OS name and version, etc.)

Tested on Ubuntu 20.04 and lambda runtime python3.9

[ChristianWeymannTNG]

As a workaround, we currently reset the config around the calls

config = session._session.get_default_client_config()
config_no_region = config.merge(Config(region_name=None))
session._session.set_default_client_config(config_no_region)
try:
    ...
finally:
    session._session.set_default_client_config(config)

[tim-finnigan]

Hi @ChristianWeymannTNG thanks for reaching out. A similar issue was raised here before: #125. The create-bucket documentation notes that regions outside of us-east-1 require the appropriate LocationConstraint to be specified in order to create the bucket in the desired region. Otherwise the default is us-east-1. Please let us know if you had any further questions on this. Since this issue involves a guidance on expected behavior rather than a bug I am going to convert it to a discussion as per our triage process.