platforms: fix unreachable hosts not reset on platform group failure

changes.d/fix.6109.md

@@ -0,0 +1 @@
+Fixed bug affecting job submission where the list of bad hosts was not always reset correctly.

cylc/flow/exceptions.py

@@ -21,6 +21,7 @@
     Callable,
     Dict,
     Iterable,
+    Set,
     NoReturn,
     Optional,
     Tuple,
@@ -444,15 +445,21 @@ class NoPlatformsError(PlatformLookupError):
 
     Args:
         identity: The name of the platform group or install target
+        hosts_consumed: Hosts which have already been tried.
         set_type: Whether the set of platforms is a platform group or an
             install target
         place: Where the attempt to get the platform failed.
     """
     def __init__(
-        self, identity: str, set_type: str = 'group', place: str = ''
+        self,
+        identity: str,
+        hosts_consumed: Set[str],
+        set_type: str = 'group',
+        place: str = '',
     ):
         self.identity = identity
         self.type = set_type
+        self.hosts_consumed = hosts_consumed
         if place:
             self.place = f' during {place}.'
         else:

cylc/flow/platforms.py

@@ -302,9 +302,14 @@ def get_platform_from_group(
     else:
         platform_names = group['platforms']
 
-    # Return False if there are no platforms available to be selected.
+    # If there are no platforms available to be selected:
     if not platform_names:
-        raise NoPlatformsError(group_name)
+        hosts_consumed = {
+            host
+            for platform in group['platforms']
+            for host in platform_from_name(platform)['hosts']}
+        raise NoPlatformsError(
+            group_name, hosts_consumed)
 
     # Get the selection method
     method = group['selection']['method']

cylc/flow/task_job_mgr.py

@@ -267,18 +267,21 @@ def submit_task_jobs(self, workflow, itasks, curve_auth,
         # Prepare tasks for job submission
         prepared_tasks, bad_tasks = self.prep_submit_task_jobs(
             workflow, itasks)
+
         # Reset consumed host selection results
         self.task_remote_mgr.subshell_eval_reset()
 
         if not prepared_tasks:
             return bad_tasks
+
         auth_itasks = {}  # {platform: [itask, ...], ...}
 
         for itask in prepared_tasks:
             platform_name = itask.platform['name']
             auth_itasks.setdefault(platform_name, [])
             auth_itasks[platform_name].append(itask)
         # Submit task jobs for each platform
+        # Non-prepared tasks can be considered done for now:
         done_tasks = bad_tasks
 
         for _, itasks in sorted(auth_itasks.items()):
@@ -1087,7 +1090,7 @@ def _prep_submit_task_job(
         Returns:
             * itask - preparation complete.
             * None - preparation in progress.
-            * False - perparation failed.
+            * False - preparation failed.
 
         """
         if itask.local_job_file_path:
@@ -1181,6 +1184,14 @@ def _prep_submit_task_job(
                 itask.summary['platforms_used'][itask.submit_num] = ''
                 # Retry delays, needed for the try_num
                 self._create_job_log_path(workflow, itask)
+                if isinstance(exc, NoPlatformsError):
+                    # Clear all hosts from all platforms in group from
+                    # bad_hosts:
+                    self.bad_hosts -= exc.hosts_consumed
+                    self._set_retry_timers(itask, rtconfig)
+                    self._prep_submit_task_job_error(
+                        workflow, itask, '(no platforms available)', exc)
+                    return False
                 self._prep_submit_task_job_error(
                     workflow, itask, '(platform not defined)', exc)
                 return False

cylc/flow/task_remote_mgr.py

@@ -388,7 +388,10 @@ def remote_tidy(self) -> None:
             else:
                 LOG.error(
                     NoPlatformsError(
-                        install_target, 'install target', 'remote tidy'))
+                        install_target,
+                        set(),
+                        'install target',
+                        'remote tidy'))
         # Wait for commands to complete for a max of 10 seconds
         timeout = time() + 10.0
         while queue and time() < timeout:

tests/integration/test_platforms.py

@@ -0,0 +1,53 @@
+# THIS FILE IS PART OF THE CYLC WORKFLOW ENGINE.
+# Copyright (C) NIWA & British Crown (Met Office) & Contributors.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+"""Integration testing for platforms functionality."""
+
+
+async def test_prep_submit_task_tries_multiple_platforms(
+    flow, scheduler, start, mock_glbl_cfg
+):
+    """Preparation tries multiple platforms within a group if the
+    task platform setting matches a group, and that after all platforms
+    have been tried that the hosts matching that platform group are
+    cleared.
+
+    See https://github.com/cylc/cylc-flow/pull/6109
+    """
+    global_conf = '''
+        [platforms]
+            [[myplatform]]
+                hosts = broken
+            [[anotherbad]]
+                hosts = broken2
+        [platform groups]
+            [[mygroup]]
+                platforms = myplatform, anotherbad'''
+    mock_glbl_cfg('cylc.flow.platforms.glbl_cfg', global_conf)
+
+    wid = flow({
+        "scheduling": {"graph": {"R1": "foo"}},
+        "runtime": {"foo": {"platform": "mygroup"}}
+    })
+    schd = scheduler(wid, run_mode='live')
+    async with start(schd):
+        itask = schd.pool.get_tasks()[0]
+        itask.submit_num = 1
+        # simulate failed attempts to contact the job hosts
+        schd.task_job_mgr.bad_hosts = {'broken', 'broken2'}
+        res = schd.task_job_mgr._prep_submit_task_job(schd.workflow, itask)
+        assert res is False
+        # ensure the bad hosts have been cleared
+        assert not schd.task_job_mgr.bad_hosts