yahoo-eng-team team mailing list archive

[Sebastian Lohff <1998621@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

When talking to dnsmasq using DNS over tcp dnsmasq will fork out for TCP
connections. Forked processes will stay until all connections have been
closed, meaning that dangling connections will keep the processes and
with that will also keep the tcp/53 port in listening state. On dnsmasq
restart (e.g. on network update, subnet create, ...) the parent process
is killed with SIGKILL and a new process is started. This new process
cannot listen on tcp/53, as it is still in use by the old child with the
dangling connection.

This could be prevented by sending SIGTERM instead of SIGKILL, as
dnsmasq then does a proper cleanup of its forks and all tcp/53
connections are properly closed.

This only happens when starting the dnsmasq with --bind-dynamic, as with this flag dnsmasq will ignore any errors resulting form it not being able to bind on tcp/53, see here:
https://github.com/imp/dnsmasq/blob/f186bdcbc76cd894133a043b115b4510c0ee1fcf/src/network.c#L725-L726
The flag has been introduced here:
https://bugs.launchpad.net/neutron/+bug/1828473

** Affects: neutron
     Importance: Undecided
         Status: In Progress

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https://bugs.launchpad.net/bugs/1998621

Title:
  dnsmasq on DHCP Agent does not listen on tcp/53 after dnsmasq restart

Status in neutron:
  In Progress

Bug description:
  When talking to dnsmasq using DNS over tcp dnsmasq will fork out for
  TCP connections. Forked processes will stay until all connections have
  been closed, meaning that dangling connections will keep the processes
  and with that will also keep the tcp/53 port in listening state. On
  dnsmasq restart (e.g. on network update, subnet create, ...) the
  parent process is killed with SIGKILL and a new process is started.
  This new process cannot listen on tcp/53, as it is still in use by the
  old child with the dangling connection.

  This could be prevented by sending SIGTERM instead of SIGKILL, as
  dnsmasq then does a proper cleanup of its forks and all tcp/53
  connections are properly closed.

  This only happens when starting the dnsmasq with --bind-dynamic, as with this flag dnsmasq will ignore any errors resulting form it not being able to bind on tcp/53, see here:
  https://github.com/imp/dnsmasq/blob/f186bdcbc76cd894133a043b115b4510c0ee1fcf/src/network.c#L725-L726
  The flag has been introduced here:
  https://bugs.launchpad.net/neutron/+bug/1828473

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