Fixup for nomad bridge lo down issue

profiles/client.nix

@@ -4,6 +4,7 @@
     ./consul/client.nix
     ./docker.nix
     ./nomad/client.nix
+    ./nomad/bridge-lo-fixup.nix
     ./telegraf.nix
     ./vault/client.nix
     ./secrets.nix

profiles/nomad/bridge-lo-fixup.nix

@@ -0,0 +1,36 @@
+{ pkgs, config, lib, ... }:
+{
+  # Workaround to address broken lo interface in Nomad created net namespaces
+  # https://github.com/hashicorp/nomad/issues/10014
+  systemd.services.monitor-exec-driver-lo = {
+    path = with pkgs; [ coreutils inotify-tools iproute2 gnugrep ];
+    wantedBy = [ "multi-user.target" ];
+    after = [ "network-online.target" ];
+    serviceConfig = {
+      Type = "simple";
+      Restart = "on-failure";
+      RestartSec = "5s";
+      ExecStart = pkgs.writeBashChecked "monitor-exec-driver-lo" ''
+        set -euo pipefail
+
+        mkdir -p /var/run/netns
+
+        # Run upon detection of any create or modify network namespace changes
+        inotifywait -m -e create -e modify --format '%w%f' /var/run/netns | \
+          while read -r NS_CHANGED; do
+            NS="$(basename "$NS_CHANGED" /var/run/netns)"
+            echo "Namespace change detected: $NS_CHANGED"
+
+            echo "Namespace loopback state before fixup:"
+            ip netns exec "$NS" ip -br a || : | grep -E '^lo.*$' || :
+
+            # All Nomad namespaces should have an operational loopback interface
+            ip netns exec "$NS" ip link set lo up || :
+
+            echo "Namespace loopback state after fixup:"
+            ip netns exec "$NS" ip -br a || : | grep -E '^lo.*$' || :
+          done
+      '';
+    };
+  };
+}