Fix environment variable order for global rank determination

CHANGELOG.md

@@ -615,6 +615,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed an `AttributeError` when calling `save_hyperparameters` and no parameters need saving ([#11827](https://github.com/PyTorchLightning/pytorch-lightning/pull/11827))
 
 
+- Fixed environment variable priority for global rank determination ([#11406](https://github.com/PyTorchLightning/pytorch-lightning/pull/11406))
+
+
 ## [1.5.9] - 2022-01-20
 
 ### Fixed

pytorch_lightning/utilities/rank_zero.py

@@ -37,7 +37,9 @@ def wrapped_fn(*args: Any, **kwargs: Any) -> Optional[Any]:
 
 # TODO: this should be part of the cluster environment
 def _get_rank() -> int:
-    rank_keys = ("RANK", "SLURM_PROCID", "LOCAL_RANK")
+    # SLURM_PROCID can be set even if SLURM is not managing the multiprocessing,
+    # therefore LOCAL_RANK needs to be checked first
+    rank_keys = ("RANK", "LOCAL_RANK", "SLURM_PROCID")
     for key in rank_keys:
         rank = os.environ.get(key)
         if rank is not None:

tests/utilities/rank_zero.py

@@ -53,3 +53,19 @@ def foo():
 
         x = foo()
         assert x is None
+
+
+@pytest.mark.parametrize(
+    "environ,expected_rank",
+    [
+        ({"SLURM_PROCID": "2"}, 2),
+        ({"SLURM_PROCID": "2", "LOCAL_RANK": "1"}, 1),
+        ({"SLURM_PROCID": "2", "LOCAL_RANK": "1", "RANK": "0"}, 0),
+    ],
+)
+def test_rank_zero_priority(environ, expected_rank):
+    """Test the priority in which the rank gets determined when multiple environment variables are available."""
+    with mock.patch.dict(os.environ, environ):
+        from pytorch_lightning.utilities.rank_zero import _get_rank
+
+        assert _get_rank() == expected_rank