bionic: DNS search domains lost from cloud-init to netplan

[Ryan Finnie]

On a deployed node with a MAAS datasource, /etc/cloud/cloud.cfg.d/50-curtin-networking.cfg contains:

network:
  config:
  - id: enp1s0
    mac_address: 52:54:00:9a:b4:64
    mtu: 1500
    name: enp1s0
    subnets:
    - address: 10.48.7.48/21
      dns_nameservers:
      - 10.48.0.5
      gateway: 10.48.0.1
      type: static
    type: physical
  - address:
    - 10.48.0.5
    search:
    - bos01.canonistack.internal
    type: nameserver
  version: 1

But the generated /etc/netplan/50-cloud-init.yaml contains no search domains under nameservers for the interface:
# This file is generated from information provided by
# the datasource. Changes to it will not persist across an instance.
# To disable cloud-init's network configuration capabilities, write a file
# /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the following:
# network: {config: disabled}
network:
    version: 2
    ethernets:
        enp1s0:
            addresses:
            - 10.48.7.48/21
            gateway4: 10.48.0.1
            match:
                macaddress: 52:54:00:9a:b4:64
            mtu: 1500
            nameservers:
                addresses:
                - 10.48.0.5
            set-name: enp1s0

Related bugs:
 * bug 1750884: /etc/resolv.conf not configured correctly in Bionic, leads to no DNS resolution

[Scott Moser (smoser)]

This is related to bug 1750884.
In netplan/systemd-networkd there is no such thing as "global" dns. The decision was made that although users configured dns globally for the vast majority of the last 30 years, we were not going to support that behavior any more in netplan or systemd-networkd.

Under that bug, though, cloud-init worked around by copying the 'nameserver' settings from the global section to each interface.

Curiously, though, we did not copy the search entries.

I am not sure why.

[Ryan Harper (raharper)]

The searchpath is copied. In netplan , the config namespace is:

nameservers:
   - addresses: [x, y]
   - search: [a, b]

The relevant code in cloudinit/net/netplan.py:

# inject global nameserver values under each all interface which
# has addresses and do not already have a DNS configuration
if nameservers or searchdomains:
    nscfg = {'addresses': nameservers, 'search': searchdomains}
    for section in [ethernets, wifis, bonds, bridges, vlans]:
        for _name, cfg in section.items():
            if 'nameservers' in cfg or 'addresses' not in cfg:
                continue
            cfg.update({'nameservers': nscfg})

Note the nscfg contains both the nameservers and the searchdomains.

[Scott Moser (smoser)]

@Ryan,

I marked this confirmed because the issue reproduces with current master and 'net-convert.py'.
I think the issue here is that the subnet had dns_nameservers. but 'search' was only declared at the global level.

The patch http://paste.ubuntu.com/p/k3hjFPv5qD/ will fix this issue.

$ cat my.cfg
network:
  config:
  - id: enp1s0
    mac_address: 52:54:00:9a:b4:64
    mtu: 1500
    name: enp1s0
    subnets:
    - address: 10.48.7.48/21
      dns_nameservers:
      - 10.48.0.5
      gateway: 10.48.0.1
      type: static
    type: physical
  - address:
    - 10.48.0.5
    search:
    - bos01.canonistack.internal
    type: nameserver
  version: 1

$ PYTHONPATH=$PWD ./tools/net-convert.py --network-data=my.cfg --kind=yaml -d out.d --output-kind=netplan

$ cat out.d/etc/netplan/50-cloud-init.yaml

network:
    version: 2
    ethernets:
        enp1s0:
            addresses:
            - 10.48.7.48/21
            gateway4: 10.48.0.1
            match:
                macaddress: 52:54:00:9a:b4:64
            mtu: 1500
            nameservers:
                addresses:
                - 10.48.0.5
            set-name: enp1s0

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/3189