Fix: Map /etc/resolv.conf file in device quirks (#3808)

The initial approach to DNS client on Linux containers blindly mapped
/etc/resolv.conf file and used the Docker DNS forwarder as the DNS
resolver. That broke on Podman (see #3803).

This fix maps the /etc/resolv.conf file into the container only when
we need to set our own DNS servers; otherwise it leaves the container
management system to do its job. The mapping is done in device quirks
and has to be applied to Linux, FRR, and all daemons.

Author: ipspace

netsim/devices/bird.py

@@ -5,6 +5,7 @@
 
 from . import _Quirks
 from ._common import check_daemon_dataplane_config
+from .linux import etc_resolv_mapping
 
 
 def bird_transform_rt(rt: str) -> str:
@@ -46,6 +47,7 @@ class Bird(_Quirks):
 
   @classmethod
   def device_quirks(self, node: Box, topology: Box) -> None:
+    etc_resolv_mapping(node,topology)
     check_daemon_dataplane_config(node,topology)
     bird_vrf_rt(node)
     bird_vlan_evpn_rt(node)

netsim/devices/dnsmasq.py

@@ -0,0 +1,14 @@
+#
+# dnsmasq quirks
+#
+from box import Box
+
+from . import _Quirks
+from .linux import etc_resolv_mapping
+
+
+class Dnsmasq(_Quirks):
+
+  @classmethod
+  def device_quirks(self, node: Box, topology: Box) -> None:
+    etc_resolv_mapping(node,topology)

netsim/devices/frr.py

@@ -5,6 +5,7 @@
 
 from ..utils import log
 from . import _Quirks, report_quirk
+from .linux import etc_resolv_mapping
 
 """
 Because FRR uses a 'bridge per VLAN' model, STP BPDUs are sent as tagged packets, not untagged.
@@ -28,6 +29,7 @@ class FRR(_Quirks):
 
   @classmethod
   def device_quirks(self, node: Box, topology: Box) -> None:
+    etc_resolv_mapping(node,topology)
     mods = node.get('module',[])
     if 'stp' in mods and node.get('stp.enable',True):
       if log.debug_active('quirks'):

netsim/devices/frr.yml

@@ -56,7 +56,6 @@ clab:
     config_templates:
       daemons: /etc/frr/daemons
       hosts: /etc/hosts:shared
-      resolv: /etc/resolv.conf
 
 libvirt:
   image: debian/bookworm64

netsim/devices/linux.py

@@ -30,11 +30,23 @@ def check_extra_loopbacks(node: Box, topology: Box) -> None:
     category=log.IncorrectType,
     quirk='ubuntu_dummy')
 
+def etc_resolv_mapping(node: Box, topology: Box) -> None:
+  """
+  Add /etc/resolv.conf mapping for Linux-based containers using DNS services
+  """
+  if devices.get_provider(node,topology) != 'clab':
+    return
+  if 'services.dns._server_list' not in node:
+    return
+  if 'clab.config_templates.resolv' not in node:
+    node.clab.config_templates.resolv = '/etc/resolv.conf'
+
 class Linux(_Quirks):
 
   @classmethod
   def device_quirks(self, node: Box, topology: Box) -> None:
     check_indirect_static_routes(node)
+    etc_resolv_mapping(node,topology)
 
     if devices.get_provider(node,topology) != 'clab':
       check_vm_modules(node,topology)

netsim/devices/linux.yml

@@ -73,7 +73,6 @@ clab:
     kind: linux
     config_templates:
       hosts: /etc/hosts:shared
-      resolv: /etc/resolv.conf
   group_vars:
     ansible_connection: docker
     ansible_user: root

tests/coverage/expected/check-config-files.yml

@@ -40,8 +40,6 @@ nodes:
       - mode: ro
         source: node_files/-shared-hosts
         target: /etc/hosts
-      - source: node_files/r1/resolv
-        target: /etc/resolv.conf
       config_templates:
       - mode: sh
         source: initial
@@ -54,8 +52,6 @@ nodes:
       - mode: shared
         source: hosts
         target: /etc/hosts
-      - source: resolv
-        target: /etc/resolv.conf
       exec:
       - sleep 1
       kind: linux
@@ -108,8 +104,6 @@ nodes:
       - mode: ro
         source: node_files/-shared-hosts
         target: /etc/hosts
-      - source: node_files/r2/resolv
-        target: /etc/resolv.conf
       config_templates:
       - mode: sh
         source: initial
@@ -119,8 +113,6 @@ nodes:
       - mode: shared
         source: hosts
         target: /etc/hosts
-      - source: resolv
-        target: /etc/resolv.conf
       exec:
       - sleep 1
       kind: linux

tests/coverage/expected/device-module-defaults.yml

@@ -83,8 +83,6 @@ nodes:
       - mode: ro
         source: node_files/-shared-hosts
         target: /etc/hosts
-      - source: node_files/l1/resolv
-        target: /etc/resolv.conf
       config_templates:
       - mode: sh
         source: initial
@@ -97,8 +95,6 @@ nodes:
       - mode: shared
         source: hosts
         target: /etc/hosts
-      - source: resolv
-        target: /etc/resolv.conf
       exec:
       - sleep 1
       kind: linux

tests/coverage/expected/device-node-defaults.yml

@@ -62,8 +62,6 @@ nodes:
       - mode: ro
         source: node_files/-shared-hosts
         target: /etc/hosts
-      - source: node_files/h1/resolv
-        target: /etc/resolv.conf
       config_templates:
       - mode: ns
         source: initial
@@ -74,8 +72,6 @@ nodes:
       - mode: shared
         source: hosts
         target: /etc/hosts
-      - source: resolv
-        target: /etc/resolv.conf
       kind: linux
     device: linux
     hostname: clab-input-h1
@@ -142,8 +138,6 @@ nodes:
       - mode: ro
         source: node_files/-shared-hosts
         target: /etc/hosts
-      - source: node_files/h2/resolv
-        target: /etc/resolv.conf
       config_templates:
       - mode: ns
         source: initial
@@ -154,8 +148,6 @@ nodes:
       - mode: shared
         source: hosts
         target: /etc/hosts
-      - source: resolv
-        target: /etc/resolv.conf
       kind: linux
     device: linux
     hostname: clab-input-h2
@@ -228,8 +220,6 @@ nodes:
       - mode: ro
         source: node_files/-shared-hosts
         target: /etc/hosts
-      - source: node_files/rtr/resolv
-        target: /etc/resolv.conf
       config_templates:
       - mode: sh
         source: initial
@@ -242,8 +232,6 @@ nodes:
       - mode: shared
         source: hosts
         target: /etc/hosts
-      - source: resolv
-        target: /etc/resolv.conf
       exec:
       - sleep 1
       image: none

tests/topology/expected/bridge-module-attr.yml

@@ -73,8 +73,6 @@ nodes:
       - mode: ro
         source: node_files/-shared-hosts
         target: /etc/hosts
-      - source: node_files/br/resolv
-        target: /etc/resolv.conf
       config_templates:
       - mode: ns
         source: initial
@@ -85,8 +83,6 @@ nodes:
       - mode: shared
         source: hosts
         target: /etc/hosts
-      - source: resolv
-        target: /etc/resolv.conf
       kind: linux
     device: linux
     hostname: clab-input-br
@@ -187,8 +183,6 @@ nodes:
       - mode: ro
         source: node_files/-shared-hosts
         target: /etc/hosts
-      - source: node_files/r1/resolv
-        target: /etc/resolv.conf
       config_templates:
       - mode: sh
         source: initial
@@ -201,8 +195,6 @@ nodes:
       - mode: shared
         source: hosts
         target: /etc/hosts
-      - source: resolv
-        target: /etc/resolv.conf
       exec:
       - sleep 1
       kind: linux
@@ -283,8 +275,6 @@ nodes:
       - mode: ro
         source: node_files/-shared-hosts
         target: /etc/hosts
-      - source: node_files/r2/resolv
-        target: /etc/resolv.conf
       config_templates:
       - mode: sh
         source: initial
@@ -297,8 +287,6 @@ nodes:
       - mode: shared
         source: hosts
         target: /etc/hosts
-      - source: resolv
-        target: /etc/resolv.conf
       exec:
       - sleep 1
       kind: linux