SlackCallBack.py

def get_slack_on_retry_callback(owners_list):
    def retry_callback(context):
        from airflow.operators import SlackAPIPostOperator
        slack_conf = getVarIfExists("slack_conf", json=True)
        message = '[{DS}]\n[{DAG}]\n[{TASK}]\n :warning: La tarea se está reintentando :warning: \n Alerta para {OWNERS} \n -----------'\
            .format(
            DAG = context['dag'].dag_id,
            TASK = context['task'].task_id,
            DS = context['ds'],
            OWNERS = ' '.join(owners_list)
            )
        slack_retry_notification =  SlackAPIPostOperator(task_id="Notificar_Retry",
                             channel=slack_conf.get('channel'),
                             username=slack_conf.get('username'),
                             text=message,
                             token=slack_conf.get('token'))
        return slack_retry_notification.execute()

    return retry_callback