By assigning a function with notification logic to the on_failure_callback parameter, you can customize the action that is taken when a task fails in your DAG1. For example, you can send an email, a Slack message, or a PagerDuty alert to notify yourself or your team about the task failure2. This option is more flexible and reliable than configuring a Cloud Monitoring alert on the sla_missed metric, which only triggers when a task misses its scheduled deadline3. The sla_miss_callback parameter is also related to the sla_missed metric, and it is executed when the task instance has not succeeded and the time is past the task's scheduled execution date plus its sla4. The on_retry_callback parameter is executed before a task is retried4. These options are not suitable for notifying when a task does not succeed, as they depend on the task's schedule and retry settings, which may not reflect the actual task completion status. References:
* 1: Callbacks | Cloud Composer | Google Cloud
* 2: How to Send an Email on Task Failure in Airflow - Astronomer
* 3: Monitoring SLA misses | Cloud Composer | Google Cloud
* 4: BaseOperator | Apache Airflow Documentation