chore(slurmctld): use peer relation for ingress ip

These changes add a peer relation for the slurmctld charm
and replace using the slurmd interface to obtain the
ingress_address with the new slurmctld-peer relation.

The reason for this change is that we do not want to depend
on the existence of the slurmd relation in order to know our ip.

Using a peer relation we will always have resolvability so long
as juju knows the ip address of the unit.

charms/slurmctld/charmcraft.yaml

@@ -30,6 +30,10 @@ requires:
   slurmrestd:
     interface: slurmrestd
 
+peers:
+  slurmctld-peer:
+    interface: slurmctld-peer
+
 assumes:
   - juju
 

charms/slurmctld/src/charm.py

@@ -9,7 +9,8 @@
 import subprocess
 from typing import Any, Dict, List, Optional, Union
 
-from constants import CHARM_MAINTAINED_SLURM_CONF_PARAMETERS, SLURM_CONF_PATH
+from constants import CHARM_MAINTAINED_SLURM_CONF_PARAMETERS, PEER_RELATION, SLURM_CONF_PATH
+from custom_exceptions import IngressAddressUnavailableError
 from interface_slurmd import (
     PartitionAvailableEvent,
     PartitionUnavailableEvent,
@@ -307,7 +308,7 @@ def _assemble_slurmctld_parameters() -> str:
 
         slurm_conf = {
             "ClusterName": self.cluster_name,
-            "SlurmctldAddr": self._slurmd_ingress_address,
+            "SlurmctldAddr": self._ingress_address,
             "SlurmctldHost": self.hostname,
             "SlurmctldParameters": _assemble_slurmctld_parameters(),
             "ProctrackType": "proctrack/linuxproc" if is_container() else "proctrack/cgroup",
@@ -403,12 +404,15 @@ def hostname(self) -> str:
         return self._slurmctld_manager.hostname
 
     @property
-    def _slurmd_ingress_address(self) -> str:
-        """Return the ingress_address from the slurmd relation if it exists."""
-        ingress_address = ""
-        if binding := self.model.get_binding("slurmd"):
-            ingress_address = f"{binding.network.ingress_address}"
-        return ingress_address
+    def _ingress_address(self) -> str:
+        """Return the ingress_address from the peer relation if it exists."""
+        if (peer_binding := self.model.get_binding(PEER_RELATION)) is not None:
+            logger.debug(
+                "Getting ingress_address: %s",
+                peer_binding.network.ingress_address,
+            )
+            return str(peer_binding.network.ingress_address)
+        raise IngressAddressUnavailableError
 
     @property
     def slurm_installed(self) -> bool:

charms/slurmctld/src/constants.py

@@ -3,6 +3,8 @@
 """This module provides constants for the slurmctld-operator charm."""
 from pathlib import Path
 
+PEER_RELATION = "slurmctld-peer"
+
 SLURM_CONF_PATH = Path("/etc/slurm/slurm.conf")
 SLURM_USER = "slurm"
 SLURM_GROUP = "slurm"