Training with a custom service account needs a new field named service account
trainingInput:
  serviceAccount: CUSTOM_SERVICE_ACCOUNT

https://cloud.google.com/ai-platform/training/docs/custom-service-account


airflow/providers/google/cloud/operators/mlengine.py
"""
    Replaces invalid MLEngine job_id characters with '_'.
    This also adds a leading 'z' in case job_id starts with an invalid
    character.
    :param job_id: A job_id str that may have invalid characters.
    :type job_id: str:
    :return: A valid job_id representation.
    :rtype: str
    """
    
    match = re.search(r'\d|\{{2}', job_id)
    if match and match.start() == 0:
        job = 'z_{}'.format(job_id)
    else:
        job = job_id
    
    tracker = 0
    cleansed_job_id = ''
    for match in re.finditer(r'\{{2}.+?\}{2}', job):
        cleansed_job_id += re.sub(r'[^0-9a-zA-Z]+', '_', job[tracker : match.start()])
        cleansed_job_id += job[match.start() : match.end()]
        tracker = match.end()
    
    cleansed_job_id += re.sub(r'[^0-9a-zA-Z]+', '_', job[tracker:])
    return cleansed_job_id
class MLEngineStartBatchPredictionJobOperator(BaseOperator):