airflow sla_miss_callback function doesn't trigger and doesn't show up in dag details page

Question

I would like to send alerts via my custom callback function that I'm calling during dag initialization as show below-

dag = DAG('tutorial', default_args=default_args, schedule_interval=timedelta(days=1), sla_miss_callback=my_sla_miss_cb_func)

My def signature is as follows-

def my_sla_miss_cb_func(): ...custom_logic....

I've got sla attribute for the tasks I would like to monitor and I see that I get SLA MISS emails when I give email_on_failure=True but my_sla_miss_cb_func function doesn't get called/triggered.

Also, sla_miss_callback attribute doesn't show up in Details page in airflow UI.

I'm using airflow 1.7.1.3