fallback to Scheduler if the GRID is not available on runtime

CHANGELOG.md

@@ -1,10 +1,11 @@
 # Changelog
 
+- 2026-02-20: Add fallback routine to use `Scheduler` if the GRID is not available
 - 2025-12-15: Added missing NGA glycan parameters - Issue #1462
 - 2025-11-25: Simplify the use of multiple ambig archives
 - 2025-11-19: Corrected CNS verbosity settings - Issue #1446
 - 2025-11-19: Added zinc-finger docking example, related to Issue #1445
-- 2025-11-19: Corrected flexref module for Issue #1445 
+- 2025-11-19: Corrected flexref module for Issue #1445
 - 2025-11-17: Added possibility to use alascan with ligands - Issue #1411
 - 2025-10-22: Allow the definition of chain combinations to be used for scoring - Issue #1414
 - 2025-09-11: Added `grid` mode

src/haddock/modules/__init__.py

@@ -28,7 +28,7 @@
 from haddock.gear.parameters import config_mandatory_general_parameters
 from haddock.gear.yaml2cfg import read_from_yaml_config, find_incompatible_parameters
 from haddock.libs.libhpc import HPCScheduler
-from haddock.libs.libgrid import GRIDScheduler
+from haddock.libs.libgrid import GRIDScheduler, ping_dirac
 from haddock.libs.libio import folder_exists, working_directory
 from haddock.libs.libmpi import MPIScheduler
 from haddock.libs.libontology import ModuleIO, PDBFile
@@ -65,9 +65,7 @@
 # modules will use these parameters. It is the responsibility of the module to
 # extract the parameters it needs.
 # the config file is in modules/defaults.cfg
-non_mandatory_general_parameters_defaults = read_from_yaml_config(
-    modules_defaults_path
-)  # noqa : E501
+non_mandatory_general_parameters_defaults = read_from_yaml_config(modules_defaults_path)  # noqa : E501
 
 incompatible_defaults_params = find_incompatible_parameters(modules_defaults_path)
 
@@ -187,9 +185,7 @@ def update_params(
         >>> m.update_params(...)
         """
         if update_from_cfg_file and params:
-            _msg = (
-                "You can not provide both `update_from_cfg_file` " "and key arguments."
-            )
+            _msg = "You can not provide both `update_from_cfg_file` and key arguments."
             raise TypeError(_msg)
 
         if update_from_cfg_file:
@@ -305,7 +301,7 @@ def export_io_models(self, faulty_tolerance: float = 0.0) -> None:
             if detected_errors := find_all_cns_errors(self.path):
                 _msg += linesep
                 for error in detected_errors.values():
-                    _msg += f'{str(error["error"])}{linesep}'
+                    _msg += f"{str(error['error'])}{linesep}"
             # Show final error message
             self.finish_with_error(_msg)
 
@@ -399,7 +395,7 @@ def _fill_emptypaths(self) -> None:
 def get_engine(
     mode: str,
     params: dict[Any, Any],
-) -> partial[Union[HPCScheduler, Scheduler, MPIScheduler]]:
+) -> partial[Union[HPCScheduler, Scheduler, MPIScheduler, GRIDScheduler]]:
     """
     Create an engine to run the jobs.
 
@@ -433,10 +429,22 @@ def get_engine(
         return partial(MPIScheduler, ncores=params["ncores"])  # type: ignore
 
     elif mode == "grid":
-        return partial(GRIDScheduler, params=params)  # type: ignore
+        # `grid` mode should only be used IF the grid is reachable,
+        #  if not it should fallback to `local`
+        grid_available = ping_dirac()
+
+        if grid_available:
+            return partial(GRIDScheduler, params=params)  # type: ignore
+        else:
+            log.warning("GRID is not available, activating fallback using `mode=local`")
+            return partial(  # type: ignore
+                Scheduler,
+                ncores=params["ncores"],
+                max_cpus=params["max_cpus"],
+            )
 
     else:
-        available_engines = ("batch", "local", "mpi")
+        available_engines = ("batch", "local", "mpi", "grid")
         raise ValueError(
             f"Scheduler `mode` {mode!r} not recognized. "
             f"Available options are {', '.join(available_engines)}"

tests/test_modules.py

@@ -0,0 +1,49 @@
+from functools import partial
+from unittest.mock import patch
+
+from haddock.libs.libgrid import GRIDScheduler
+from haddock.libs.libhpc import HPCScheduler
+from haddock.libs.libmpi import MPIScheduler
+from haddock.libs.libparallel import Scheduler
+from haddock.modules import get_engine
+
+
+def test_get_engine_grid_unavailable():
+    with patch("haddock.modules.ping_dirac", return_value=False):
+        engine = get_engine(mode="grid", params={"ncores": 1, "max_cpus": 4})
+        assert isinstance(engine, partial)
+        assert engine.func is Scheduler
+
+
+def test_get_engine_grid_available():
+    with patch("haddock.modules.ping_dirac", return_value=True):
+        engine = get_engine(mode="grid", params={"ncores": 1, "max_cpus": 4})
+        assert isinstance(engine, partial)
+        assert engine.func is GRIDScheduler
+
+
+def test_get_engine_local():
+    engine = get_engine(mode="local", params={"ncores": 2, "max_cpus": 8})
+    assert isinstance(engine, partial)
+    assert engine.func is Scheduler
+    assert engine.keywords["ncores"] == 2
+    assert engine.keywords["max_cpus"] == 8
+
+
+def test_get_engine_batch():
+    engine = get_engine(
+        mode="batch",
+        params={"queue": "short", "queue_limit": 100, "concat": 5},
+    )
+    assert isinstance(engine, partial)
+    assert engine.func is HPCScheduler
+    assert engine.keywords["target_queue"] == "short"
+    assert engine.keywords["queue_limit"] == 100
+    assert engine.keywords["concat"] == 5
+
+
+def test_get_engine_mpi():
+    engine = get_engine(mode="mpi", params={"ncores": 4})
+    assert isinstance(engine, partial)
+    assert engine.func is MPIScheduler
+    assert engine.keywords["ncores"] == 4