Fix: Restarting the NDP Proxy sometimes crashed

This is likely due because it was restarted too quickly.

Solution: Wrap the error in a custom class and retry after 5 seconds.

This is still a work in progress as a better approach should limit the frequency of restarts instead, for example using an event or queue.

src/aleph/vm/network/ndp_proxy.py

@@ -10,16 +10,24 @@
 and restart the service.
 """
 
+import asyncio
 import logging
 from dataclasses import dataclass
 from ipaddress import IPv6Network
 from pathlib import Path
+from subprocess import CalledProcessError
 
 from aleph.vm.utils import run_in_subprocess
 
 logger = logging.getLogger(__name__)
 
 
+class NdpProxyTerminatedError(Exception):
+    """Raised when restarting the NDP Proxy fails due to a SIGTERM signal."""
+
+    pass
+
+
 @dataclass
 class NdpRule:
     address_range: IPv6Network
@@ -33,15 +41,32 @@ def __init__(self, host_network_interface: str):
     @staticmethod
     async def _restart_ndppd():
         logger.debug("Restarting ndppd")
-        await run_in_subprocess(["systemctl", "restart", "ndppd"])
+        try:
+            await run_in_subprocess(["systemctl", "restart", "ndppd"])
+        except CalledProcessError as error:
+            if "died with <Signals.SIGTERM: 15>." in str(error):
+                raise NdpProxyTerminatedError("ndppd was terminated by a SIGTERM signal") from error
+            else:
+                raise
 
     async def _update_ndppd_conf(self):
         config = f"proxy {self.host_network_interface} {{\n"
         for interface, address_range in self.interface_address_range_mapping.items():
             config += f"  rule {address_range} {{\n    iface {interface}\n  }}\n"
         config += "}\n"
         Path("/etc/ndppd.conf").write_text(config)
-        await self._restart_ndppd()
+        for attempt in range(3):
+            try:
+                await self._restart_ndppd()
+                break
+            except NdpProxyTerminatedError:
+                if attempt >= 2:
+                    raise
+                logger.warning(
+                    "ndppd was terminated by a SIGTERM signal while restarting. Waiting 5 seconds and retrying."
+                )
+                await asyncio.sleep(5)
+                continue
 
     async def add_range(self, interface: str, address_range: IPv6Network):
         logger.debug("Proxying range %s -> %s", address_range, interface)