[Bug 1721092] Re: systemd-resolved and dns-masq make CPU 100% when using lxc name resolution

[Alex Garel]

Hello, can I do anything for this to progress toward a solution ?

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Title:
  systemd-resolved and dns-masq make CPU 100% when using lxc name
  resolution

Status in systemd package in Ubuntu:
  New

Bug description:
  This bug may be a duplicate of
  https://bugs.launchpad.net/ubuntu/+source/dnsmasq/+bug/1688364 but I'm
  not sure, hence this new entry.

  It hits while I wanted systemd to resolve the lxc domain to my
  internal lxc hosts.

  Step to (maybe) reproduce:

  - having lxc installed
  - make some user space lxc container
  - uncomment the line LXC_DOMAIN="lxc" in /etc/default/lxc-net
  - restart lxc-net service

  Now the dnsmasq on 10.0.3.1 should be a dns resolving lxc names.

  - add a file /etc/systemd/resolved.conf.d/lxc.conf

    [Resolve]
    DNS=10.0.3.1
    Domains=~.lxc
    DNSSEC=false

  - restart systemd-resolved service

  Now systemd knows it should ask .lxc names to dnsmasq

  - start an lxc container, let assume it's called my-container
  - ping it using my-container.lxc it should work

  After some times, systemd-resolved should use 100% CPU.

  Commenting the /etc/systemd/resolved.conf.d/lxc.conf file and
  restarting it makes systemd-resolved never eating resources again.

  ProblemType: Bug
  DistroRelease: Ubuntu 17.04
  Package: systemd 232-21ubuntu5
  Uname: Linux 4.10.16-041016-generic x86_64
  ApportVersion: 2.20.4-0ubuntu4.5
  Architecture: amd64
  CurrentDesktop: GNOME
  Date: Tue Oct  3 18:18:56 2017
  InstallationDate: Installed on 2015-11-10 (692 days ago)
  InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
  MachineType: Intel Corporation Skylake Platform
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.10.16-041016-generic root=UUID=6814e3c1-8cea-4ecc-964d-535fd18782e9 ro quiet splash crashkernel=384M-:128M vt.handoff=7
  SourcePackage: systemd
  UpgradeStatus: Upgraded to zesty on 2017-02-25 (219 days ago)
  dmi.bios.date: 11/06/2015
  dmi.bios.vendor: American Megatrends Inc.
  dmi.bios.version: 5.11
  dmi.board.asset.tag: Base Board Asset Tag
  dmi.board.name: WhiteTip Mountain1 Fab2
  dmi.board.vendor: Topstar
  dmi.board.version: RVP7
  dmi.chassis.asset.tag: Default string
  dmi.chassis.type: 9
  dmi.chassis.vendor: Default string
  dmi.chassis.version: Default string
  dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr5.11:bd11/06/2015:svnIntelCorporation:pnSkylakePlatform:pvr0.1:rvnTopstar:rnWhiteTipMountain1Fab2:rvrRVP7:cvnDefaultstring:ct9:cvrDefaultstring:
  dmi.product.name: Skylake Platform
  dmi.product.version: 0.1
  dmi.sys.vendor: Intel Corporation

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