From 42930d8459b59b22cab3f76d85d170871174b479 Mon Sep 17 00:00:00 2001
From: Alberto Contreras <alberto.contreras@canonical.com>
Date: Wed, 29 May 2024 09:10:53 +0200
Subject: [PATCH] fix(azure): disable use-dns for secondary nics (#5314)

DNS resolution through secondary NICs is not supported on Azure. Disable
it.

Without this, we see seconds of delay resolving urls in cloud-init logs
from Jammy+, see SF ticket.

Per cjp256's comment, the first NIC under metadata.imds.network is
ensured
to be the primary one. We use this to determine primary NICs instead of
relying on fragile driver and/or NIC names.

Fixes: SF: #00380708

Co-authored-by: Calvin Mwadime <calvin.mwadime@canonical.com>
---
 cloudinit/sources/DataSourceAzure.py  |  3 +++
 tests/unittests/sources/test_azure.py | 20 +++++++++++++-------
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/cloudinit/sources/DataSourceAzure.py b/cloudinit/sources/DataSourceAzure.py
index 11c14e2..e384b32 100644
--- a/cloudinit/sources/DataSourceAzure.py
+++ b/cloudinit/sources/DataSourceAzure.py
@@ -1965,6 +1965,9 @@ def generate_network_config_from_instance_network_metadata(
         # addresses.
         nicname = "eth{idx}".format(idx=idx)
         dhcp_override = {"route-metric": (idx + 1) * 100}
+        # DNS resolution through secondary NICs is not supported, disable it.
+        if idx > 0:
+            dhcp_override["use-dns"] = False
         dev_config: Dict[str, Any] = {
             "dhcp4": True,
             "dhcp4-overrides": dhcp_override,
diff --git a/tests/unittests/sources/test_azure.py b/tests/unittests/sources/test_azure.py
index 2a477f8..3a36418 100644
--- a/tests/unittests/sources/test_azure.py
+++ b/tests/unittests/sources/test_azure.py
@@ -718,14 +718,20 @@ class TestGenerateNetworkConfig:
                             "match": {"macaddress": "00:0d:3a:04:75:98"},
                             "dhcp6": False,
                             "dhcp4": True,
-                            "dhcp4-overrides": {"route-metric": 200},
+                            "dhcp4-overrides": {
+                                "route-metric": 200,
+                                "use-dns": False,
+                            },
                         },
                         "eth2": {
                             "set-name": "eth2",
                             "match": {"macaddress": "00:0d:3a:04:75:98"},
                             "dhcp6": False,
                             "dhcp4": True,
-                            "dhcp4-overrides": {"route-metric": 300},
+                            "dhcp4-overrides": {
+                                "route-metric": 300,
+                                "use-dns": False,
+                            },
                         },
                     },
                     "version": 2,
@@ -952,7 +958,7 @@ class TestNetworkConfig:
                     "dhcp6": False,
                     "match": {"macaddress": "00:0d:3a:04:75:98"},
                     "set-name": "eth0",
-                }
+                },
             },
             "version": 2,
         }
@@ -1534,7 +1540,7 @@ scbus-1 on xpt0 bus 0
                     "dhcp6": False,
                     "dhcp4": True,
                     "dhcp4-overrides": {"route-metric": 100},
-                }
+                },
             },
             "version": 2,
         }
@@ -1563,14 +1569,14 @@ scbus-1 on xpt0 bus 0
                     "match": {"macaddress": "22:0d:3a:04:75:98"},
                     "dhcp6": False,
                     "dhcp4": True,
-                    "dhcp4-overrides": {"route-metric": 200},
+                    "dhcp4-overrides": {"route-metric": 200, "use-dns": False},
                 },
                 "eth2": {
                     "set-name": "eth2",
                     "match": {"macaddress": "33:0d:3a:04:75:98"},
                     "dhcp6": False,
                     "dhcp4": True,
-                    "dhcp4-overrides": {"route-metric": 300},
+                    "dhcp4-overrides": {"route-metric": 300, "use-dns": False},
                 },
             },
             "version": 2,
@@ -1603,7 +1609,7 @@ scbus-1 on xpt0 bus 0
                     "dhcp6": False,
                     "dhcp4": True,
                     "dhcp4-overrides": {"route-metric": 100},
-                }
+                },
             },
             "version": 2,
         }
-- 
2.27.0