Gen ddp support (#1961)

* updated docs

* added mixed

* added mixed

Author: williamFalcon

pytorch_lightning/trainer/trainer.py

@@ -856,17 +856,21 @@ def fit(
         if self.use_ddp2:
             if self.is_slurm_managing_tasks:
                 task = int(os.environ['SLURM_LOCALID'])
-            elif 'WORLD_SIZE' in os.environ and 'GROUP_RANK' in os.environ:
+
+            # torchelastic or general non_slurm ddp2
+            elif 'WORLD_SIZE' in os.environ and ('GROUP_RANK' in os.environ or 'NODE_RANK' in os.environ):
                 task = int(os.environ['LOCAL_RANK'])
             self.ddp_train(task, model)
         elif self.use_ddp:
             if self.is_slurm_managing_tasks:
                 task = int(os.environ['SLURM_LOCALID'])
                 self.ddp_train(task, model)
-            # torchelastic
-            elif 'WORLD_SIZE' in os.environ and 'GROUP_RANK' in os.environ:
+
+            # torchelastic or general non_slurm ddp
+            elif 'WORLD_SIZE' in os.environ and ('GROUP_RANK' in os.environ or 'NODE_RANK' in os.environ):
                 task = int(os.environ['LOCAL_RANK'])
                 self.ddp_train(task, model)
+
             else:
                 self.__set_random_port()
                 # track for predict