[AIRFLOW-3177] Change scheduler_heartbeat from gauge to counter (apac…

…he#4027)

This updates the scheduler_heartbeat metric from a gauge to a counter to
better support the statsd_exporter for usage with Prometheus. A counter
allows users to track the rate of the heartbeat, and integrates with the
exporter better. A crashing or down scheduler will no longer emit the
metric, but the statsd_exporter will continue to show a 1 for the metric
value. This fixes that issue because a counter will continually change,
and the lack of change indicates an issue with the scheduler.

Add statsd change notice in UPDATING.md

UPDATING.md

@@ -21,6 +21,68 @@ that he has permissions on. If a new role wants to access all the dags, the admi
 
 We also provide a new cli command(``sync_perm``) to allow admin to auto sync permissions.
 
+
+### min_file_parsing_loop_time config option temporarily disabled
+
+The scheduler.min_file_parsing_loop_time config option has been temporarily removed due to
+some bugs.
+
+### new `sync_parallelism` config option in celery section
+
+The new `sync_parallelism` config option will control how many processes CeleryExecutor will use to
+fetch celery task state in parallel. Default value is max(1, number of cores - 1)
+
+### CLI Changes
+
+The ability to manipulate users from the command line has been changed. 'airflow create_user' and 'airflow delete_user' and 'airflow list_users' has been grouped to a single command `airflow users` with optional flags `--create`, `--list` and `--delete`.
+
+Example Usage:
+
+To create a new user:
+```bash
+airflow users --create --username jondoe --lastname doe --firstname jon --email jdoe@apache.org --role Viewer --password test
+```
+
+To list users:
+```bash
+airflow users --list
+```
+
+To delete a user:
+```bash
+airflow users --delete --username jondoe
+```
+
+### StatsD Metrics
+
+The `scheduler_heartbeat` metric has been changed from a gauge to a counter. Each loop of the scheduler will increment the counter by 1. This provides a higher degree of visibility and allows for better integration with Prometheus using the [StatsD Exporter](https://github.com/prometheus/statsd_exporter). Scheduler upness can be determined by graphing and alerting using a rate. If the scheduler goes down, the rate will drop to 0.
+
+### Custom auth backends interface change
+
+We have updated the version of flask-login we depend upon, and as a result any
+custom auth backends might need a small change: `is_active`,
+`is_authenticated`, and `is_anonymous` should now be properties. What this means is if
+previously you had this in your user class
+
+    def is_active(self):
+      return self.active
+
+then you need to change it like this
+
+    @property
+    def is_active(self):
+      return self.active
+
+## Airflow 1.10
+
+Installation and upgrading requires setting `SLUGIFY_USES_TEXT_UNIDECODE=yes` in your environment or
+`AIRFLOW_GPL_UNIDECODE=yes`. In case of the latter a GPL runtime dependency will be installed due to a
+dependency (python-nvd3 -> python-slugify -> unidecode).
+
+### Replace DataProcHook.await calls to DataProcHook.wait
+
+The method name was changed to be compatible with the Python 3.7 async/await keywords
+
 ### Setting UTF-8 as default mime_charset in email utils
 
 ### Add a configuration variable(default_dag_run_display_number) to control numbers of dag run for display

airflow/jobs.py

@@ -1892,7 +1892,7 @@ def process_file(self, file_path, pickle_dags=False, session=None):
 
     @provide_session
     def heartbeat_callback(self, session=None):
-        Stats.gauge('scheduler_heartbeat', 1, 1)
+        Stats.incr('scheduler_heartbeat', 1, 1)
 
 
 class BackfillJob(BaseJob):