If ipv6 is disabled through the kernel, neutron-dhcp-agent fails to create the tap devices due to error regarding ipv6

[David Hill]

If we disable ipv6 using ipv6.disable=1 at the kernel runtime, neutron-dhcp-agent stops creating the tap devices and fails here:

dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.linux.utils [-] Exit code: 255; Stdin: ; Stdout: ; Stderr: sysctl: cannot stat /proc/sys/net/ipv6/conf/default/accept_ra: No such file or directory
dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.dhcp.agent [-] Unable to enable dhcp for 310b9752-06a5-4d7b-98ae-1ba8536e22fa.
dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.dhcp.agent Traceback (most recent call last):
dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.dhcp.agent File "/usr/lib/python2.7/site-packages/neutron/agent/dhcp/agent.py", line 140, in call_driver
dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.dhcp.agent getattr(driver, action)(**action_kwargs)
dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.dhcp.agent File "/usr/lib/python2.7/site-packages/neutron/agent/linux/dhcp.py", line 213, in enable
dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.dhcp.agent interface_name = self.device_manager.setup(self.network)
dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.dhcp.agent File "/usr/lib/python2.7/site-packages/neutron/agent/linux/dhcp.py", line 1441, in setup
dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.dhcp.agent n_const.ACCEPT_RA_DISABLED)
dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.dhcp.agent File "/usr/lib/python2.7/site-packages/neutron/agent/linux/interface.py", line 260, in configure_ipv6_ra
dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.dhcp.agent 'value': value}])
dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.dhcp.agent File "/usr/lib/python2.7/site-packages/neutron/agent/linux/ip_lib.py", line 912, in execute
dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.dhcp.agent log_fail_as_error=log_fail_as_error, **kwargs)
dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.dhcp.agent File "/usr/lib/python2.7/site-packages/neutron/agent/linux/utils.py", line 148, in execute
dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.dhcp.agent raise ProcessExecutionError(msg, returncode=returncode)
dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.dhcp.agent ProcessExecutionError: Exit code: 255; Stdin: ; Stdout: ; Stderr: sysctl: cannot stat /proc/sys/net/ipv6/conf/default/accept_ra: No such file or directory
dhcp-agent.log:2019-03-04 19:29:13.342 5869 ERROR neutron.agent.dhcp.agent

[David Hill (david-hill-ubisoft)]

This is in newton and it appears it's already fixed in Queens [1]

[1] https://bugs.launchpad.net/neutron/+bug/1618878

[David Hill (david-hill-ubisoft)]

I still did write this patch :

[root@overcloud-controller-0 linux]# git diff
diff --git a/agent/linux/dhcp.py b/agent/linux/dhcp.py
index aa9f2cd..2cc00f1 100644
--- a/agent/linux/dhcp.py
+++ b/agent/linux/dhcp.py
@@ -21,6 +21,7 @@ import shutil
 import time

 import netaddr
+from neutron.common import ipv6_utils
 from neutron_lib import constants
 from neutron_lib import exceptions
 from oslo_config import cfg
@@ -1437,8 +1438,10 @@ class DeviceManager(object):
         # and added back statically in the call to init_l3() below.
         if network.namespace:
             ip_lib.IPWrapper().ensure_namespace(network.namespace)
- self.driver.configure_ipv6_ra(network.namespace, 'default',
- n_const.ACCEPT_RA_DISABLED)
+ self.use_ipv6 = ipv6_utils.is_enabled()
+ if self.use_ipv6:
+ self.driver.configure_ipv6_ra(network.namespace, 'default',
+ n_const.ACCEPT_RA_DISABLED)

         if ip_lib.ensure_device_is_ready(interface_name,
                                          namespace=network.namespace):