DRIVERS-2425 : Several of the drivers are using the pattern of creating a prepare_mongodb_aws.sh file and sourcing as part of their AWS Evergreen tests. For the case of testing against EC2 credentials, several of the drivers are not writing this file as part of the task, but the file exists on disk from a previous task run on the same job. The task is therefore run using the contents of prepare_mongodb_aws.sh , which could contain AWS auth environment variables, preventing the driver from fetching the credentials using the AWS end point. The file should be overwritten or removed during the EC2 credential test. See https://github.com/mongodb/mongo-python-driver/commit/0f135a157e2fa6ae66d4091186bdf0c40113ef77 for an example fix.