Support for ALPINE_NO_RESOLVER env var

When this env var is passed to the container, then the container DNS
server will not be started, but resolv.conf will still be changed to
have the nameserver 127.0.0.1. This is a specific workaround making it
possible to run multiple Alpine-Kubernetes images in a single Pod that
shares a common network port stack so that only one DNS server can bind
to localhost port 53.

rootfs/etc/services.d/resolver/run

@@ -1,5 +1,12 @@
 #!/usr/bin/execlineb -P
 
 with-contenv
+backtick -D "" -n ALPINE_NO_RESOLVER { printcontenv ALPINE_NO_RESOLVER }
+importas -u ALPINE_NO_RESOLVER ALPINE_NO_RESOLVER
+ifelse { s6-test -n ${ALPINE_NO_RESOLVER} }
+{
+	fdmove -c 2 1
+	/sbin/kubernetes_multi_pod.sh
+}
 fdmove -c 2 1
-go-dnsmasq --default-resolver --append-search-domains --hostsfile=/etc/hosts
+go-dnsmasq --default-resolver --append-search-domains --hostsfile=/etc/hosts

rootfs/sbin/kubernetes_multi_pod.sh

@@ -0,0 +1,33 @@
+#!/bin/ash
+
+# Program that changes the systems primary nameserver to 127.0.0.1
+# and restores the original resolv.conf on exit
+
+RESOLV=/etc/resolv.conf
+BACKUP=/etc/resolv.conf.orig
+
+clean_up() {
+	if [ -f "$BACKUP" ]
+	then
+		cat $BACKUP > $RESOLV
+		echo "[Alpine-Kubernetes] Restored resolv.conf"
+	fi
+   exit
+}
+
+trap clean_up SIGHUP SIGINT SIGTERM
+
+echo "[Alpine-Kubernetes] Changed nameserver to 127.0.0.1"
+
+if [ ! -f "$RESOLV" ]
+then
+	echo "Could not stat $RESOLV"
+	exit 1
+fi
+
+cp $RESOLV $BACKUP
+
+echo '# Created by Alpine-Kubernetes' > $RESOLV
+echo 'nameserver 127.0.0.1' >> $RESOLV
+
+tail -f /dev/null

versions/3.2/rootfs/etc/services.d/resolver/run

@@ -1,5 +1,12 @@
 #!/usr/bin/execlineb -P
 
 with-contenv
+backtick -D "" -n ALPINE_NO_RESOLVER { printcontenv ALPINE_NO_RESOLVER }
+importas -u ALPINE_NO_RESOLVER ALPINE_NO_RESOLVER
+ifelse { s6-test -n ${ALPINE_NO_RESOLVER} }
+{
+	fdmove -c 2 1
+	/sbin/kubernetes_multi_pod.sh
+}
 fdmove -c 2 1
-go-dnsmasq --default-resolver --append-search-domains --hostsfile=/etc/hosts
+go-dnsmasq --default-resolver --append-search-domains --hostsfile=/etc/hosts

versions/3.2/rootfs/sbin/kubernetes_multi_pod.sh

@@ -0,0 +1,33 @@
+#!/bin/ash
+
+# Program that changes the systems primary nameserver to 127.0.0.1
+# and restores the original resolv.conf on exit
+
+RESOLV=/etc/resolv.conf
+BACKUP=/etc/resolv.conf.orig
+
+clean_up() {
+	if [ -f "$BACKUP" ]
+	then
+		cat $BACKUP > $RESOLV
+		echo "[Alpine-Kubernetes] Restored resolv.conf"
+	fi
+   exit
+}
+
+trap clean_up SIGHUP SIGINT SIGTERM
+
+echo "[Alpine-Kubernetes] Changed nameserver to 127.0.0.1"
+
+if [ ! -f "$RESOLV" ]
+then
+	echo "Could not stat $RESOLV"
+	exit 1
+fi
+
+cp $RESOLV $BACKUP
+
+echo '# Created by Alpine-Kubernetes' > $RESOLV
+echo 'nameserver 127.0.0.1' >> $RESOLV
+
+tail -f /dev/null

versions/3.3/rootfs/etc/services.d/resolver/run

@@ -1,5 +1,12 @@
 #!/usr/bin/execlineb -P
 
 with-contenv
+backtick -D "" -n ALPINE_NO_RESOLVER { printcontenv ALPINE_NO_RESOLVER }
+importas -u ALPINE_NO_RESOLVER ALPINE_NO_RESOLVER
+ifelse { s6-test -n ${ALPINE_NO_RESOLVER} }
+{
+	fdmove -c 2 1
+	/sbin/kubernetes_multi_pod.sh
+}
 fdmove -c 2 1
-go-dnsmasq --default-resolver --append-search-domains --hostsfile=/etc/hosts
+go-dnsmasq --default-resolver --append-search-domains --hostsfile=/etc/hosts

versions/3.3/rootfs/sbin/kubernetes_multi_pod.sh

@@ -0,0 +1,33 @@
+#!/bin/ash
+
+# Program that changes the systems primary nameserver to 127.0.0.1
+# and restores the original resolv.conf on exit
+
+RESOLV=/etc/resolv.conf
+BACKUP=/etc/resolv.conf.orig
+
+clean_up() {
+	if [ -f "$BACKUP" ]
+	then
+		cat $BACKUP > $RESOLV
+		echo "[Alpine-Kubernetes] Restored resolv.conf"
+	fi
+   exit
+}
+
+trap clean_up SIGHUP SIGINT SIGTERM
+
+echo "[Alpine-Kubernetes] Changed nameserver to 127.0.0.1"
+
+if [ ! -f "$RESOLV" ]
+then
+	echo "Could not stat $RESOLV"
+	exit 1
+fi
+
+cp $RESOLV $BACKUP
+
+echo '# Created by Alpine-Kubernetes' > $RESOLV
+echo 'nameserver 127.0.0.1' >> $RESOLV
+
+tail -f /dev/null