Allow for a custom MetricsCollector class to be loaded at runtime

doc/configuration.rst

@@ -836,7 +836,12 @@ metrics_collector
   Optional setting allowing Luigi to use a contribution to collect metrics
   about the pipeline to a third-party. By default this uses the default metric
   collector that acts as a shell and does nothing. The currently available
-  options are "datadog" and "prometheus".
+  options are "datadog", "prometheus" and "custom". If it's custom the
+  'metrics_custom_import' needs to be set.
+
+metrics_custom_import
+  Optional setting allowing Luigi to import a custom subclass of MetricsCollector
+  at runtime. The string should be formatted like "module.sub_module.ClassName".
 
 
 [sendgrid]

luigi/metrics.py

@@ -1,16 +1,18 @@
 import abc
+import importlib
 
 from enum import Enum
 
 
 class MetricsCollectors(Enum):
+    custom = -1
     default = 1
     none = 1
     datadog = 2
     prometheus = 3
 
     @classmethod
-    def get(cls, which):
+    def get(cls, which, custom_import=None):
         if which == MetricsCollectors.none:
             return NoMetricsCollector()
         elif which == MetricsCollectors.datadog:
@@ -19,6 +21,22 @@ def get(cls, which):
         elif which == MetricsCollectors.prometheus:
             from luigi.contrib.prometheus_metric import PrometheusMetricsCollector
             return PrometheusMetricsCollector()
+        elif which == MetricsCollectors.custom:
+            if custom_import is None:
+                raise ValueError(f"MetricsCollectors value ' {which} ' is -1 and custom_import is None")
+
+            split_import_string = custom_import.split(".")
+
+            import_path = ".".join(split_import_string[:-1])
+            import_class_string = split_import_string[-1]
+
+            mod = importlib.import_module(import_path)
+            metrics_class = getattr(mod, import_class_string)
+
+            if issubclass(metrics_class, MetricsCollector):
+                return metrics_class()
+            else:
+                raise ValueError(f"Custom Import: {custom_import} is not a subclass of MetricsCollector")
         else:
             raise ValueError("MetricsCollectors value ' {0} ' isn't supported", which)
 

luigi/scheduler.py

@@ -145,6 +145,7 @@ class scheduler(Config):
     send_messages = parameter.BoolParameter(default=True)
 
     metrics_collector = parameter.EnumParameter(enum=MetricsCollectors, default=MetricsCollectors.default)
+    metrics_custom_import = parameter.OptionalStrParameter(default=None)
 
     stable_done_cooldown_secs = parameter.IntParameter(default=10,
                                                        description="Sets cooldown period to avoid running the same task twice")
@@ -695,7 +696,7 @@ def __init__(self, config=None, resources=None, task_history_impl=None, **kwargs
         if self._config.batch_emails:
             self._email_batcher = BatchNotifier()
 
-        self._state._metrics_collector = MetricsCollectors.get(self._config.metrics_collector)
+        self._state._metrics_collector = MetricsCollectors.get(self._config.metrics_collector, self._config.metrics_custom_import)
 
     def load(self):
         self._state.load()

test/scheduler_test.py

@@ -281,6 +281,15 @@ def test_prometheus_metrics_collector(self):
         collector = scheduler_state._metrics_collector
         self.assertTrue(isinstance(collector, PrometheusMetricsCollector))
 
+    @with_config({'scheduler': {'metrics_collector': 'custom', 'metrics_custom_import': 'luigi.contrib.prometheus_metric.PrometheusMetricsCollector'}})
+    def test_custom_metrics_collector(self):
+        from luigi.contrib.prometheus_metric import PrometheusMetricsCollector
+
+        s = luigi.scheduler.Scheduler()
+        scheduler_state = s._state
+        collector = scheduler_state._metrics_collector
+        self.assertTrue(isinstance(collector, PrometheusMetricsCollector))
+
 
 class SchedulerWorkerTest(unittest.TestCase):
     def get_pending_ids(self, worker, state):