From 589e4eda02ef383a8fb2de39633b6d4ac8f82220 Mon Sep 17 00:00:00 2001
From: Steven Fairchild <sfairchi@redhat.com>
Date: Wed, 28 Jun 2023 10:13:28 -0400
Subject: [PATCH] Fix resolv.conf during Azure host servicing

If the network interfaces are brought up/down without restarting NetworkManager, our resolv.conf will be overwritten by NetworkManager.
This can occur during [Azure Host Servicing](https://learn.microsoft.com/en-us/azure/developer/intro/hosting-apps-on-azure) events.

Addiontal information is written to the system logs to assist with SRE
troubleshooting.

By using NetworkManager dispatcher scripts, we can restart dnsmasq when
certian events happen.
---
 pkg/operator/controllers/dnsmasq/dnsmasq.go | 72 +++++++++++++++++++++
 1 file changed, 72 insertions(+)

diff --git a/pkg/operator/controllers/dnsmasq/dnsmasq.go b/pkg/operator/controllers/dnsmasq/dnsmasq.go
index 9182fb7c040..c28d6ab832a 100644
--- a/pkg/operator/controllers/dnsmasq/dnsmasq.go
+++ b/pkg/operator/controllers/dnsmasq/dnsmasq.go
@@ -110,6 +110,46 @@ chmod 0744 /etc/resolv.conf.dnsmasq
 /bin/rm $TMPNETRESOLV
 /bin/rm $TMPSELFRESOLV
 {{ end }}
+
+{{ define "99-dnsmasq-restart" }}
+#!/bin/sh
+# This is a NetworkManager dispatcher script to restart dnsmasq
+# in the event of a network interface change (e. g. host servicing event https://learn.microsoft.com/en-us/azure/developer/intro/hosting-apps-on-azure)
+# this will restart dnsmasq, reapplying our /etc/resolv.conf file and overwriting any modifications made by NetworkManager
+
+interface=$1
+action=$2
+
+log() {
+    logger -i "$0" -t '99-DNSMASQ-RESTART SCRIPT' "$@"
+}
+
+if [[ $interface == eth* && $action == "up" ]] || [[ $interface == eth* && $action == "down" ]] || [ $interface == enP* && $action == "up" ] || [ $interface == enP* && $action == "down" ]; then
+    log "$action happened on $interface, connection state is now $CONNECTIVITY_STATE"
+    log "restarting dnsmasq now"
+    if systemctl restart dnsmasq; then
+        log "dnsmasq successfully restarted"
+    else
+        log "failed to restart dnsmasq"
+    fi
+
+    # log dns configuration information relevant to SRE while troubleshooting
+    # The line break used here is important for formatting
+    log "/etc/resolv.conf contents
+
+    $(cat /etc/resolv.conf)"
+
+	log "$(echo -n \"/etc/resolv.conf file metadata: \") $(ls -lZ /etc/resolv.conf)"
+
+    log "/etc/resolv.conf.dnsmasq contents
+
+    $(cat /etc/resolv.conf.dnsmasq)"
+
+	log "$(echo -n "/etc/resolv.conf.dnsmasq file metadata: ") $(ls -lZ /etc/resolv.conf.dnsmasq)"
+fi
+
+exit 0
+{{ end }}
 `))
 
 func config(clusterDomain, apiIntIP, ingressIP string, gatewayDomains []string, gatewayPrivateEndpointIP string) ([]byte, error) {
@@ -157,6 +197,17 @@ func startpre() ([]byte, error) {
 	return buf.Bytes(), nil
 }
 
+func nmDispatcherRestartDnsmasq() ([]byte, error) {
+	buf := &bytes.Buffer{}
+
+	err := t.ExecuteTemplate(buf, "99-dnsmasq-restart", nil)
+	if err != nil {
+		return nil, err
+	}
+
+	return buf.Bytes(), nil
+}
+
 func ignition2Config(clusterDomain, apiIntIP, ingressIP string, gatewayDomains []string, gatewayPrivateEndpointIP string) (*ign2types.Config, error) {
 	service, err := service()
 	if err != nil {
@@ -173,6 +224,11 @@ func ignition2Config(clusterDomain, apiIntIP, ingressIP string, gatewayDomains [
 		return nil, err
 	}
 
+	nmDispatcherRestartDnsmasq, err := nmDispatcherRestartDnsmasq()
+	if err != nil {
+		return nil, err
+	}
+
 	return &ign2types.Config{
 		Ignition: ign2types.Ignition{
 			Version: ign2types.MaxVersion.String(),
@@ -211,6 +267,22 @@ func ignition2Config(clusterDomain, apiIntIP, ingressIP string, gatewayDomains [
 						Mode: ignutil.IntToPtr(0744),
 					},
 				},
+				{
+					Node: ign2types.Node{
+						Filesystem: "root",
+						Overwrite:  ignutil.BoolToPtr(true),
+						Path:       "/etc/NetworkManager/dispatcher.d/99-dnsmasq-restart",
+						User: &ign2types.NodeUser{
+							Name: *ignutil.StrToPtr("root"),
+						},
+					},
+					FileEmbedded1: ign2types.FileEmbedded1{
+						Contents: ign2types.FileContents{
+							Source: *ignutil.StrToPtr(dataurl.EncodeBytes(nmDispatcherRestartDnsmasq)),
+						},
+						Mode: ignutil.IntToPtr(0744),
+					},
+				},
 			},
 		},
 		Systemd: ign2types.Systemd{