[Bug 1718842] [NEW] autopkgtest environments end up with duplicate default routes

[Steve Langasek]

Public bug reported:

With the migration to netplan/systemd-networkd/systemd-resolved,
autopkgtest VMs now end up with multiple default routes.  This causes
miscellaneous autopkgtest failures of packages that assume a single
record will be returned when grepping route -n output for 0.0.0.0.

These autopkgtests can be made more robust (it's not correct to assume
that there will only be one default route on a system); but it's also a
bug that there are duplicate routes.

This problem is reproducible in other artful VMs using netplan+networkd.
E.g.:

$ gcloud compute instances create artful-test --image-project ubuntu-os-cloud-devel --image daily-ubuntu-1710-artful-v20170921a
Created [https://www.googleapis.com/compute/v1/projects/ubuntu-foundations/zones/us-west1-a/instances/artful-test].
NAME         ZONE        MACHINE_TYPE   PREEMPTIBLE  INTERNAL_IP  EXTERNAL_IP      STATUS
artful-test  us-west1-a  n1-standard-1               10.138.0.2   104.198.107.129  RUNNING
$ gcloud compute ssh artful-test
Warning: Permanently added 'compute.2478931335975611629' (ECDSA) to the list of known hosts.
Welcome to Ubuntu Artful Aardvark (development branch) (GNU/Linux 4.13.0-11-generic x86_64)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage

  Get cloud support with Ubuntu Advantage Cloud Guest:
    http://www.ubuntu.com/business/services/cloud

0 packages can be updated.
0 updates are security updates.


The programs included with the Ubuntu system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Ubuntu comes with ABSOLUTELY NO WARRANTY, to the extent permitted by
applicable law.

vorlon at artful-test:~$  ip route show
default via 10.138.0.1 dev ens4 proto dhcp src 10.138.0.2 metric 100 
default via 10.138.0.1 dev ens4 proto dhcp metric 100 
10.138.0.1 dev ens4 proto dhcp scope link src 10.138.0.2 metric 100 
10.138.0.1 dev ens4 proto dhcp scope link metric 100 
vorlon at artful-test:~$

** Affects: systemd (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1718842

Title:
  autopkgtest environments end up with duplicate default routes

Status in systemd package in Ubuntu:
  New

Bug description:
  With the migration to netplan/systemd-networkd/systemd-resolved,
  autopkgtest VMs now end up with multiple default routes.  This causes
  miscellaneous autopkgtest failures of packages that assume a single
  record will be returned when grepping route -n output for 0.0.0.0.

  These autopkgtests can be made more robust (it's not correct to assume
  that there will only be one default route on a system); but it's also
  a bug that there are duplicate routes.

  This problem is reproducible in other artful VMs using
  netplan+networkd.  E.g.:

  $ gcloud compute instances create artful-test --image-project ubuntu-os-cloud-devel --image daily-ubuntu-1710-artful-v20170921a
  Created [https://www.googleapis.com/compute/v1/projects/ubuntu-foundations/zones/us-west1-a/instances/artful-test].
  NAME         ZONE        MACHINE_TYPE   PREEMPTIBLE  INTERNAL_IP  EXTERNAL_IP      STATUS
  artful-test  us-west1-a  n1-standard-1               10.138.0.2   104.198.107.129  RUNNING
  $ gcloud compute ssh artful-test
  Warning: Permanently added 'compute.2478931335975611629' (ECDSA) to the list of known hosts.
  Welcome to Ubuntu Artful Aardvark (development branch) (GNU/Linux 4.13.0-11-generic x86_64)

   * Documentation:  https://help.ubuntu.com
   * Management:     https://landscape.canonical.com
   * Support:        https://ubuntu.com/advantage

    Get cloud support with Ubuntu Advantage Cloud Guest:
      http://www.ubuntu.com/business/services/cloud

  0 packages can be updated.
  0 updates are security updates.


  The programs included with the Ubuntu system are free software;
  the exact distribution terms for each program are described in the
  individual files in /usr/share/doc/*/copyright.

  Ubuntu comes with ABSOLUTELY NO WARRANTY, to the extent permitted by
  applicable law.

  vorlon at artful-test:~$  ip route show
  default via 10.138.0.1 dev ens4 proto dhcp src 10.138.0.2 metric 100 
  default via 10.138.0.1 dev ens4 proto dhcp metric 100 
  10.138.0.1 dev ens4 proto dhcp scope link src 10.138.0.2 metric 100 
  10.138.0.1 dev ens4 proto dhcp scope link metric 100 
  vorlon at artful-test:~$

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