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Prevent NM from handling DNS when only network interfaces have DNS co…
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…nfig

In the change under PR #5401, if no global DNS configuration is present and only
network interfaces have DNS and search domain configuration, we add DNS and
search domain information from interface config and use it to populate
/etc/resolv.conf. Therefore, in the absence of global DNS/search domain config
and presence of only per-interface DNS/search domain information, we should add
a network manager configuration to prevent network manager from manipulating
/etc/resolv.conf.
This is in addition to what we already do when a global DNS data is configured.

Fixes: 1b8030e ("feat(sysconfig): Add DNS from interface config to resolv.conf (#5401))
Signed-off-by: Ani Sinha <[email protected]>
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@ani-sinha
ani-sinha committed Oct 28, 2024
1 parent 4b56c5c commit a76cf20
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Showing 2 changed files with 180 additions and 5 deletions.
28 changes: 23 additions & 5 deletions cloudinit/net/sysconfig.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -906,17 +906,35 @@ def _render_dns(network_state, existing_dns_path=None):

@staticmethod
def _render_networkmanager_conf(network_state, templates=None):
iface_dns = False
content = networkmanager_conf.NetworkManagerConf("")

# If DNS server information is provided, configure
# NetworkManager to not manage dns, so that /etc/resolv.conf
# does not get clobbered.
# check if there is interface specific DNS information configured
for iface in network_state.iter_interfaces():
for subnet in iface["subnets"]:
if "dns_nameservers" in subnet or "dns_search" in subnet:
iface_dns = True
break
if (
not iface_dns
and "dns" in iface
and (iface["dns"]["nameservers"] or iface["dns"]["search"])
):
iface_dns = True
break

# If DNS server and/or dns search information is provided either
# globally or per interface basis, configure NetworkManager to
# not manage dns, so that /etc/resolv.conf does not get clobbered.
# This is not required for NetworkManager renderer as it
# does not write /etc/resolv.conf directly. DNS information is
# written to the interface keyfile and NetworkManager is then
# responsible for using the DNS information from the keyfile,
# including managing /etc/resolv.conf.
if network_state.dns_nameservers:
if (
network_state.dns_nameservers
or network_state.dns_searchdomains
or iface_dns
):
content.set_section_keypair("main", "dns", "none")

if len(content) == 0:
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157 changes: 157 additions & 0 deletions tests/unittests/test_net.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -994,6 +994,163 @@
),
],
},
{
"in_data": {
"networks": [
{
"network_id": "dacd568d-5be6-4786-91fe-750c374b78b4",
"type": "ipv4",
"netmask": "255.255.252.0",
"link": "eth0",
"routes": [
{
"netmask": "0.0.0.0",
"network": "0.0.0.0",
"gateway": "172.19.3.254",
}
],
"ip_address": "172.19.1.34",
"dns_search": ["example3.com"],
"dns_nameservers": ["172.19.0.12"],
"id": "network0",
}
],
"links": [
{
"ethernet_mac_address": "fa:16:3e:ed:9a:59",
"mtu": None,
"type": "physical",
"id": "eth0",
},
],
},
"in_macs": {
"fa:16:3e:ed:9a:59": "eth0",
},
"out_sysconfig_opensuse": [
(
"etc/sysconfig/network/ifcfg-eth0",
"""
# Created by cloud-init automatically, do not edit.
#
BOOTPROTO=static
IPADDR=172.19.1.34
LLADDR=fa:16:3e:ed:9a:59
NETMASK=255.255.252.0
STARTMODE=auto
""".lstrip(),
),
(
"etc/resolv.conf",
"""
; Created by cloud-init automatically, do not edit.
;
nameserver 172.19.0.12
search example3.com
""".lstrip(),
),
(
"etc/NetworkManager/conf.d/99-cloud-init.conf",
"""
# Created by cloud-init automatically, do not edit.
#
[main]
dns = none
""".lstrip(),
),
(
"etc/udev/rules.d/85-persistent-net-cloud-init.rules",
"".join(
[
'SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ',
'ATTR{address}=="fa:16:3e:ed:9a:59", NAME="eth0"\n',
]
),
),
],
"out_sysconfig_rhel": [
(
"etc/sysconfig/network-scripts/ifcfg-eth0",
"""
# Created by cloud-init automatically, do not edit.
#
BOOTPROTO=none
DEFROUTE=yes
DEVICE=eth0
DNS1=172.19.0.12
DOMAIN=example3.com
GATEWAY=172.19.3.254
HWADDR=fa:16:3e:ed:9a:59
IPADDR=172.19.1.34
NETMASK=255.255.252.0
ONBOOT=yes
TYPE=Ethernet
USERCTL=no
""".lstrip(),
),
(
"etc/resolv.conf",
"""
; Created by cloud-init automatically, do not edit.
;
nameserver 172.19.0.12
search example3.com
""".lstrip(),
),
(
"etc/NetworkManager/conf.d/99-cloud-init.conf",
"""
# Created by cloud-init automatically, do not edit.
#
[main]
dns = none
""".lstrip(),
),
(
"etc/udev/rules.d/70-persistent-net.rules",
"".join(
[
'SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ',
'ATTR{address}=="fa:16:3e:ed:9a:59", NAME="eth0"\n',
]
),
),
],
"expected_network_manager": [
(
"".join(
[
"etc/NetworkManager/system-connections",
"/cloud-init-eth0.nmconnection",
]
),
"""
# Generated by cloud-init. Changes will be lost.
[connection]
id=cloud-init eth0
uuid=1dd9a779-d327-56e1-8454-c65e2556c12c
autoconnect-priority=120
type=ethernet
[user]
org.freedesktop.NetworkManager.origin=cloud-init
[ethernet]
mac-address=FA:16:3E:ED:9A:59
[ipv4]
method=manual
may-fail=false
address1=172.19.1.34/22
route1=0.0.0.0/0,172.19.3.254
dns=172.19.0.12;
dns-search=example3.com;
""".lstrip(),
),
],
},
{
"in_data": {
"services": [{"type": "dns", "address": "172.19.0.12"}],
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