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NM should not be restarted during hostname publish if NM_CONTROLLED=y #3008

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merged 8 commits into from
Jan 9, 2024
32 changes: 30 additions & 2 deletions azurelinuxagent/common/osutil/redhat.py
Original file line number Diff line number Diff line change
Expand Up @@ -117,11 +117,39 @@ def set_hostname(self, hostname):
logger.warn("[{0}] failed, attempting fallback".format(' '.join(hostnamectl_cmd)))
DefaultOSUtil.set_hostname(self, hostname)

def get_nm_controlled(self):
ifname = self.get_if_name()
filepath = "/etc/sysconfig/network-scripts/ifcfg-{0}".format(ifname)
nm_controlled_cmd = ['grep', 'NM_CONTROLLED=', filepath]
try:
result = shellutil.run_command(nm_controlled_cmd, log_error=False, encode_output=False).rstrip()
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why is encide_output needed?

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@maddieford maddieford Jan 8, 2024

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If encode_output is True the stdout is returned as a string, otherwise it is returned as a bytes object.

When True, the result is unicode (u'no'). It was easier to do the comparison if encode_output=False and the result is in bytes


if result and len(result.split('=')) > 1:
# Remove trailing white space and ' or " characters
value = result.split('=')[1].replace("'", '').replace('"', '').rstrip()
if value == "n" or value == "no":
return False
except shellutil.CommandError as e:
# Command might fail because NM_CONTROLLED value is not in interface config file (exit code 1).
# Log warning for any other exit code.
# NM_CONTROLLED=y by default if not specified.
if e.returncode != 1:
logger.warn("[{0}] failed: {1}.\nAgent will continue to publish hostname without NetworkManager restart".format(' '.join(nm_controlled_cmd), e))
except Exception as e:
logger.warn("Unexpected error while retrieving value of NM_CONTROLLED in {0}: {1}.\nAgent will continue to publish hostname without NetworkManager restart".format(filepath, e))

return True

def publish_hostname(self, hostname):
"""
Restart NetworkManager first before publishing hostname
Restart NetworkManager first before publishing hostname, only if the network interface is not controlled by the
NetworkManager service (as determined by NM_CONTROLLED=n in the interface configuration). If the NetworkManager
service is restarted before the agent publishes the hostname, and NM_controlled=y, a race condition may happen
between the NetworkManager service and the Guest Agent making changes to the network interface configuration
simultaneously.
"""
shellutil.run("service NetworkManager restart")
if not self.get_nm_controlled():
shellutil.run("service NetworkManager restart")
super(RedhatOSUtil, self).publish_hostname(hostname)

def register_agent_service(self):
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