[Bug 1828259] Re: [rocky][19.04] Upgrading a deployment from Queens to Rocky resulted in purging of neutron-l3-agent package

[Corey Bryant]

As for priority of py2 packages in rocky. In Rocky, the way things work
is that py2 packages are installed by default. If both the py2 and py3
packages are installed, then py2 packages get priority. And if only py3
packages are installed, then they will be used as the dependency.

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https://bugs.launchpad.net/bugs/1828259

Title:
  [rocky][19.04] Upgrading a deployment from Queens to Rocky resulted in
  purging of neutron-l3-agent package

Status in neutron package in Ubuntu:
  Confirmed

Bug description:
  Upgrading OpenStack from Queens to Rocky results in removal of
  neutron-l3-agent package which leads to a networking outage.

  The issue with the fact that first python3 packages are installed and
  then python2 packages are purged. The neutron-l3-agent package depends
  on both.

  At the same time neutron-dhcp-agent survives the upgrade while both
  packages seem to have identical "Depends" directives for
  python[3]-neutron:

  https://git.launchpad.net/~ubuntu-server-dev/ubuntu/+source/neutron/tree/debian/control?h=stable/rocky#n178
  Package: neutron-l3-agent
  Architecture: all
  Depends:
   conntrack,
   iputils-arping,
   keepalived,
   neutron-metadata-agent (= ${source:Version}),
   python-neutron (= ${source:Version}) | python3-neutron (= ${source:Version}),
   python-neutron-fwaas (>= 1:13.0.0~) | python3-neutron-fwaas (>= 1:13.0.0~),

  https://git.launchpad.net/~ubuntu-server-dev/ubuntu/+source/neutron/tree/debian/control?h=stable/rocky#n156
  Package: neutron-dhcp-agent
  Architecture: all
  Depends:
   dnsmasq-base (>= 2.76),
   dnsmasq-utils (>= 2.76),
   neutron-metadata-agent (= ${source:Version}),
   python-neutron (= ${source:Version}) | python3-neutron (= ${source:Version}),

  When I try to install neutron-l3-agent it tries to pull python2 dependencies again (even though the python3 ones are already there):
  https://paste.ubuntu.com/p/J7Vq8KKnBf/

  More info below:

  ------
  2019-05-07 16:42:41 DEBUG neutron-plugin-api-relation-changed Selecting previously unselected package neutron-l3-agent.
  2019-05-07 16:42:41 DEBUG neutron-plugin-api-relation-changed Preparing to unpack .../6-neutron-l3-agent_2%3a12.0.5-0ubuntu1_all.deb ...
  2019-05-07 16:42:41 DEBUG neutron-plugin-api-relation-changed Unpacking neutron-l3-agent (2:12.0.5-0ubuntu1) ...

  2019-05-07 16:42:47 DEBUG neutron-plugin-api-relation-changed Setting up neutron-l3-agent (2:12.0.5-0ubuntu1) ...
  2019-05-07 16:42:47 DEBUG neutron-plugin-api-relation-changed Created symlink /etc/systemd/system/multi-user.target.wants/neutron-l3-agent.service → /lib/systemd/syst
  em/neutron-l3-agent.service.

  /var/log/apt/term.log:

  update-alternatives: using /usr/bin/python3-nova-metadata-wsgi to provide /usr/bin/nova-metadata-wsgi (nova-metadata-wsgi) in auto mode
  (Reading database ... ^M(Reading database ... 5%^M(Reading database ... 10%^M(Reading database ... 15%^M(Reading database ... 20%^M(Reading database ... 25%^M(Reading database ... 30%^M(Reading database ... 35%^M(Reading database ... 40%^M(Reading database ... 45%^M(Reading database ... 50%^M(Reading database ... 55%^M(Reading database ... 60%^M(Reading database ... 65%^M(Reading database ... 70%^M(Reading database ... 75%^M(Reading database ... 80%^M(Reading database ... 85%^M(Reading database ... 90%^M(Reading database ... 95%^M(Reading database ... 100%^M(Reading database ... 113229 files and directories currently installed.)
  Purging configuration files for python-neutron (2:13.0.2-0ubuntu1~cloud0) ...
  Purging configuration files for neutron-l3-agent (2:13.0.2-0ubuntu1~cloud0) ...
  Purging configuration files for python-neutron-fwaas (1:13.0.1-0ubuntu1~cloud0) ...
  Purging configuration files for python-nova (2:18.1.0-0ubuntu1~cloud0) ...
  Processing triggers for ureadahead (0.100.0-21) ...
  Processing triggers for systemd (237-3ubuntu10.21) ...
  Log ended: 2019-05-08  13:46:55

  /var/log/apt/history.log:

  # install python3 packages
  Start-Date: 2019-05-08  13:45:18
  Commandline: apt-get --assume-yes --option=Dpkg::Options::=--force-confold install nova-compute genisoimage librbd1 xfsprogs nfs-common ceph-common nova-compute-kvm n
  ova-api-metadata python3-nova python3-memcache python3-rados python3-rbd python3-neutron

  # purge python2 packages
  Start-Date: 2019-05-08  13:46:40
  Commandline: apt-get --assume-yes purge python-neutron python-nova
  Purge: neutron-l3-agent:amd64 (2:13.0.2-0ubuntu1~cloud0), python-nova:amd64 (2:18.1.0-0ubuntu1~cloud0), python-neutron:amd64 (2:13.0.2-0ubuntu1~cloud0), python-neutron-fwaas:amd64 (1:13.0.1-0ubuntu1~cloud0)
  End-Date: 2019-05-08  13:46:55

  apt policy python3-neutron
  https://paste.ubuntu.com/p/3vKsFBf9Hn/

  apt-rdepends:

  neutron-l3-agent
    Depends: conntrack
    Depends: iputils-arping
    Depends: keepalived
    Depends: neutron-metadata-agent (= 2:13.0.2-0ubuntu1~cloud0)
    Depends: python-neutron (= 2:13.0.2-0ubuntu1~cloud0)
    Depends: python-neutron-fwaas (>= 1:13.0.0~)
    Depends: python3-neutron (= 2:13.0.2-0ubuntu1~cloud0)
    Depends: python3-neutron-fwaas (>= 1:13.0.0~)
  # ...

  neutron-dhcp-agent
    Depends: dnsmasq-base (>= 2.76)
    Depends: dnsmasq-utils (>= 2.76)
    Depends: neutron-metadata-agent (= 2:13.0.2-0ubuntu1~cloud0)
    Depends: python-neutron (= 2:13.0.2-0ubuntu1~cloud0)
    Depends: python3-neutron (= 2:13.0.2-0ubuntu1~cloud0)
  # ...

  Charm code:
  https://opendev.org/openstack/charm-neutron-openvswitch/src/branch/stable/19.04/hooks/neutron_ovs_utils.py#L323-L325

      if cmp_release >= 'rocky':
          return PURGE_PACKAGES
      return []

  https://opendev.org/openstack/charm-neutron-openvswitch/src/branch/master/hooks/neutron_ovs_utils.py#L119-L122
  PURGE_PACKAGES = [
      'python-neutron',
      'python-neutron-fwaas',
  ]

  https://opendev.org/openstack/charm-neutron-
  openvswitch/src/branch/master/hooks/neutron_ovs_hooks.py#L115-L124

      install_packages()
      install_tmpfilesd()

      # NOTE(jamespage): purge any packages as a result of py3 switch
      #                  at rocky.
      packages_to_purge = determine_purge_packages()
      request_nova_compute_restart = False
      if packages_to_purge:
          purge_packages(packages_to_purge)
          request_nova_compute_restart = True

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