bugfix/flux-nodes-prior-versions (#487)

* add a version check for flux when getting node count

* update CHANGELOG

* add major version check for flux

CHANGELOG.md

@@ -34,6 +34,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Link to Merlin banner in readme
 - Issue with escape sequences in ascii art (caught by python 3.12)
 - Bug where Flux wasn't identifying total number of nodes on an allocation
+  - Not supporting Flux versions below 0.17.0
 
 
 ## [1.12.1]

merlin/study/batch.py

@@ -40,7 +40,7 @@
 import subprocess
 from typing import Dict, Optional, Union
 
-from merlin.utils import convert_timestring, get_flux_alloc, get_yaml_var
+from merlin.utils import convert_timestring, get_flux_alloc, get_flux_version, get_yaml_var
 
 
 LOG = logging.getLogger(__name__)
@@ -126,7 +126,7 @@ def get_batch_type(scheduler_legend, default=None):
     return default
 
 
-def get_node_count(default=1):
+def get_node_count(parsed_batch: Dict, default=1):
     """
     Determine a default node count based on the environment.
 
@@ -135,6 +135,12 @@ def get_node_count(default=1):
     :param returns: (int) The number of nodes to use.
     """
 
+    # Flux version check
+    flux_ver = get_flux_version(parsed_batch["flux exe"], no_errors=True)
+    major, minor, _ = map(int, flux_ver.split("."))
+    if major < 1 and minor < 17:
+        raise ValueError("Flux version is too old. Supported versions are 0.17.0+.")
+
     # If flux is the scheduler, we can get the size of the allocation with this
     try:
         get_size_proc = subprocess.run("flux getattr size", shell=True, capture_output=True, text=True)
@@ -254,7 +260,7 @@ def batch_worker_launch(
 
     # Get the number of nodes from the environment if unset
     if nodes is None or nodes == "all":
-        nodes = get_node_count(default=1)
+        nodes = get_node_count(parsed_batch, default=1)
     elif not isinstance(nodes, int):
         raise TypeError("Nodes was passed into batch_worker_launch with an invalid type (likely a string other than 'all').")