disable dhclient from modifying the /etc/resolv.conf file on openstack/amazon instances

The dhclient in these environments is quite aggressive and overwrites the
nameservers we've deliberately chosen to use with google's nameservers. This
commit attempts to fix that.

The dhclient methodology for altering these things is particularly
unpleasant. We effectively redefine the functions that mess with this file to be
noops in the /etc/dhcp/dhclient-enter-hooks.d directory and then we are forced
to restart dhclient by shipping a script that tries to determine the correct PID
and arguments that it was running as before killing and restarting it with the
same arguments.

See debian bugs #681698, #712796 for further discussion about how to make this
less difficult

Change-Id: I51cf40cf98eaddcefd8180e157b6e3ca824173f0

3 files changed, 48 insertions, 1 deletions

diff --git a/puppet/modules/site_config/manifests/default.pp b/puppet/modules/site_config/manifests/default.pp
index cfb46130..5518ea56 100644
--- a/puppet/modules/site_config/manifests/default.pp
+++ b/puppet/modules/site_config/manifests/default.pp
@@ -12,10 +12,14 @@ class site_config::default {
   # configure apt
   include site_apt
 
-
   # configure ssh and include ssh-keys
   include site_config::sshd
 
+  # fix dhclient from changing resolver information
+  if $::ec2_instance_id {
+    include site_config::dhclient
+  }
+
   # configure /etc/resolv.conf
   include site_config::resolvconf
 
diff --git a/puppet/modules/site_config/manifests/dhclient.pp b/puppet/modules/site_config/manifests/dhclient.pp
new file mode 100644
index 00000000..7ac0caf3
--- /dev/null
+++ b/puppet/modules/site_config/manifests/dhclient.pp
@@ -0,0 +1,30 @@
+class site_config::dhclient {
+
+  # Unfortunately, there does not seem to be a way to reload the dhclient.conf
+  # config file, or a convenient way to disable the modifications to
+  # /etc/resolv.conf. So the following makes the functions involved noops and
+  # ships a script to kill and restart dhclient. See the debian bugs:
+  # #681698, #712796
+
+  include site_config::params
+
+  file { '/usr/local/sbin/reload_dhclient':
+    owner   => 0,
+    group   => 0,
+    mode    => '0755',
+    content => template('site_config/reload_dhclient.erb');
+  }
+
+  exec { 'reload_dhclient':
+    refreshonly => true,
+    command     => '/usr/local/sbin/reload_dhclient';
+  }
+
+  file { '/etc/dhcp/dhclient-enter-hooks.d/disable_resolvconf':
+    content => 'make_resolv_conf() { : ; } ; set_hostname() { : ; }',
+    mode    => '0644',
+    owner   => 'root',
+    group   => 'root',
+    notify  => Exec['reload_dhclient'];
+  }
+}
diff --git a/puppet/modules/site_config/templates/reload_dhclient.erb b/puppet/modules/site_config/templates/reload_dhclient.erb
new file mode 100644
index 00000000..882c985a
--- /dev/null
+++ b/puppet/modules/site_config/templates/reload_dhclient.erb
@@ -0,0 +1,13 @@
+#!/bin/sh
+
+# Get the PID
+PIDFILE='/var/run/dhclient.<%= scope.lookupvar('site_config::params::interface') %>.pid
+
+# Capture how dhclient is currently running so we can relaunch it
+dhclient=`/bin/ps --no-headers --pid $(cat $PIDFILE) -f | /usr/bin/awk '{for(i=8;i<=NF;++i) printf("%s ",  $i) }'`
+
+# Kill the current dhclient
+/usr/bin/pkill -F $PIDFILE
+
+# Restart dhclient with the arguments it had previously
+$dhclient