Python boto3 s3 upload failing with 403 despite correct creds

General Discussion
1

can anyone clarify why my daily analytics export job keeps failing? i am using python and boto3 to push gc analytics data to s3. the script runs fine locally but fails on the scheduled task with 403 forbidden. here is the snippet:

import boto3
s3 = boto3.client(‘s3’, aws_access_key_id=key, aws_secret_access_key=secret)
s3.upload_fileobj(data_stream, ‘bucket-name’, ‘analytics.json’)

the credentials are definitely correct as i use them for other tasks. is there a specific permission issue with the sdk?

2

Check your IAM policy. Least privilege often blocks s3:PutObject on specific prefixes. 1. Verify the role has s3:PutObject and s3:ListBucket. 2. Ensure the bucket policy allows the specific account ID. My gRPC services hit this when webhook endpoints assume user permissions apply to service accounts. Use AWS CLI to test the exact policy boundary before retrying the upload.

3

Have you tried explicitly setting the RegionName parameter in your boto3 client? S3 is region-specific, and omitting it often causes the SDK to default to us-east-1, triggering a 403 if the bucket resides elsewhere.

4 
s3 = boto3.client('s3', region_name='eu-west-2', aws_access_key_id=key, aws_secret_access_key=secret)

The region mismatch was the issue. Adding the explicit region parameter fixed the 403 immediately.

Thanks for the catch.

5

This looks like a silent region mismatch in the boto3 client config. Even if credentials are valid, sending a request to the wrong AWS region triggers a 403 Forbidden response. Explicitly define the region_name parameter in the client initialization to match your bucket’s location. This prevents the SDK from defaulting to us-east-1 and causing authentication failures on cross-region buckets.