A Libvirt hook to auto setup a port on ip to access virtual machines.

hook.sh

#!/bin/bash
#
# Hook script for QEMU
# 
# adds port forwards via IPtables and ARP to your VMs
#
# Implement: Erico Mendonca (erico.mendonca@suse.com)
# Change: Mohammadhossein Shahmohammadi (hos1377@gmail.com)
# 2020/Jul
#

log() {
	logger -t addForward "$1"
}

addForward() {

	IPTABLES="/sbin/iptables"
	VM=$1
	HOST_PORT=$2
	GUEST_PORT=$3

	if [ "${ACTION}" == "stopped" ]; then
		IPTABLES_ACTION="-D"
	fi

	if [ "${ACTION}" == "started" ]; then
		IPTABLES_ACTION="-I"
	fi

	if [ -z "${IPTABLES_ACTION}" ]; then
		log "There is nothing to do. Maybe domain $VM is in prepare, started or stopped, ignoring." 
		exit 0
	fi


	if [ "${VM}" == "${VM_NAME}" ]; then

		HOST_BRIDGE=$(echo "${MACHINEINFO%x}" | xpath -e /domain/devices/interface[1]/source | cut -d= -f3 | cut -d\" -f2)
		if [ -z "$HOST_BRIDGE" ] && [ $IPTABLES_ACTION == "-I" ]; then
			log "Could not identify bridge interface for ${VM}, skipping"
			exit 0
		fi

		log "Trying to add rule in iptables for ${VM_NAME}"
		MAC_ADDR=$(echo "${MACHINEINFO%x}" | xpath -e /domain/devices/interface[1]/mac/@address | cut -d '"' -f2)
		timeout=0
		while [ -z "${GUEST_IP}" ]
		do
			sleep 2
			GUEST_IP=$(arp -an | grep "$MAC_ADDR" | cut -d "(" -f2 | cut -d ")" -f1)
			((timeout+=1))
			log "${timeout} times hit, still no GUEST_IP for ${VM}"
			if [ "$timeout" == 30 ]; then
				log "Could not get GUEST_IP for ${VM}, skipping"
				exit 0
			fi
		done

		log "Found an instance with ip ${GUEST_IP} and mac ${MAC_ADDR}"
		log "adding ${IPTABLES_ACTION} forwarding rules for VM ${VM_NAME}: host port ${HOST_PORT} will be redirected to ${GUEST_IP}:${GUEST_PORT} on interface ${HOST_BRIDGE}"
		$IPTABLES ${IPTABLES_ACTION} FORWARD -o "${HOST_BRIDGE}" -d "$GUEST_IP" -j ACCEPT
		$IPTABLES -t nat ${IPTABLES_ACTION} PREROUTING -p tcp --dport "$HOST_PORT" -j DNAT --to "$GUEST_IP":"$GUEST_PORT"
	fi
}


## main program
VM_NAME=${1}
ACTION=${2}
log "${VM_NAME} try to ${ACTION}"

# read the XML from stdin
MACHINEINFO=$(cat; echo x)
log "MACHINE_INFO: ${MACHINEINFO%x}"

### declare your port forwards here
### format: <VM> <host/extenral port> <guest/internal port>
addForward my-great-vm 31001 22