From 9f87544c95072d963353dcd2f00fe5d1c20610a3 Mon Sep 17 00:00:00 2001
From: Tim Bielawa <tbielawa@redhat.com>
Date: Tue, 1 Nov 2016 08:55:12 -0700
Subject: Only restart dnsmasq if the DNS servers have changed

---
 .../files/networkmanager/99-origin-dns.sh          | 47 +++++++++++++++++++---
 1 file changed, 41 insertions(+), 6 deletions(-)

diff --git a/roles/openshift_node_dnsmasq/files/networkmanager/99-origin-dns.sh b/roles/openshift_node_dnsmasq/files/networkmanager/99-origin-dns.sh
index 5a187710b..ced0fa663 100755
--- a/roles/openshift_node_dnsmasq/files/networkmanager/99-origin-dns.sh
+++ b/roles/openshift_node_dnsmasq/files/networkmanager/99-origin-dns.sh
@@ -1,4 +1,5 @@
 #!/bin/bash -x
+# -*- mode: sh; sh-indentation: 2 -*-
 
 # This NetworkManager dispatcher script replicates the functionality of
 # NetworkManager's dns=dnsmasq  however, rather than hardcoding the listening
@@ -28,7 +29,16 @@ cd /etc/sysconfig/network-scripts
 [ -f ../network ] && . ../network
 
 if [[ $2 =~ ^(up|dhcp4-change)$ ]]; then
-  # couldn't find an existing method to determine if the interface owns the 
+  # If the origin-upstream-dns config file changed we need to restart
+  NEEDS_RESTART=0
+  UPSTREAM_DNS='/etc/dnsmasq.d/origin-upstream-dns.conf'
+  # We'll regenerate the dnsmasq origin config in a temp file first
+  UPSTREAM_DNS_TMP=`mktemp`
+  UPSTREAM_DNS_TMP_SORTED=`mktemp`
+  CURRENT_UPSTREAM_DNS_SORTED=`mktemp`
+
+  ######################################################################
+  # couldn't find an existing method to determine if the interface owns the
   # default route
   def_route=$(/sbin/ip route list match 0.0.0.0/0 | awk '{print $3 }')
   def_route_int=$(/sbin/ip route get to ${def_route} | awk '{print $3}')
@@ -43,15 +53,37 @@ domain-needed
 server=/cluster.local/172.30.0.1
 server=/30.172.in-addr.arpa/172.30.0.1
 EOF
+      # New config file, must restart
+      NEEDS_RESTART=1
     fi
-    # zero out our upstream servers list and feed it into dnsmasq
-    echo -n > /etc/dnsmasq.d/origin-upstream-dns.conf
+
+    ######################################################################
+    # Generate a new origin dns config file
     for ns in ${IP4_NAMESERVERS}; do
       if [[ ! -z $ns ]]; then
-        echo "server=${ns}" >> /etc/dnsmasq.d/origin-upstream-dns.conf
+        echo "server=${ns}"
       fi
-    done
-    systemctl restart dnsmasq
+    done > $UPSTREAM_DNS_TMP
+
+    # Sort it in case DNS servers arrived in a different order
+    sort $UPSTREAM_DNS_TMP > $UPSTREAM_DNS_TMP_SORTED
+    sort $UPSTREAM_DNS > $CURRENT_UPSTREAM_DNS_SORTED
+
+    # Compare to the current config file (sorted)
+    NEW_DNS_SUM=`md5sum ${UPSTREAM_DNS_TMP_SORTED} | awk '{print $1}'`
+    CURRENT_DNS_SUM=`md5sum ${CURRENT_UPSTREAM_DNS_SORTED} | awk '{print $1}'`
+
+    if [ "${NEW_DNS_SUM}" != "${CURRENT_DNS_SUM}" ]; then
+      # DNS has changed, copy the temp file to the proper location (-Z
+      # sets default selinux context) and set the restart flag
+      cp -Z $UPSTREAM_DNS_TMP $UPSTREAM_DNS
+      NEEDS_RESTART=1
+    fi
+
+    ######################################################################
+    if [ "${NEEDS_RESTART}" -eq "1" ]; then
+      systemctl restart dnsmasq
+    fi
 
     sed -i '0,/^nameserver/ s/^nameserver.*$/nameserver '"${def_route_ip}"'/g' /etc/resolv.conf
 
@@ -59,4 +91,7 @@ EOF
       echo "# nameserver updated by /etc/NetworkManager/dispatcher.d/99-origin-dns.sh" >> /etc/resolv.conf
     fi
   fi
+
+  # Clean up after yourself
+  rm -f $UPSTREAM_DNS_TMP $UPSTREAM_DNS_TMP_SORTED $CURRENT_UPSTREAM_DNS_SORTED
 fi
-- 
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