How to define shorewall rules to allow VRRP traffic

It is essential for routers that implement the Virtual Router Redundancy Protocol to be able to communicate with each other.

As the protocol defines, the master router needs to send multicast packets to the whole subnet and of course, the rest of the backup routers need to receive this announcements otherwise they will think that the master router is dead and will initiate an election of a master router.

If no router is able to receive this “multicasted” announcements they all will eventually think that they are the only ones alive and thus become master. All of them master. That brings networking issues.

This page covers how to define the rule(s) under shorewall firewall in order to allow this VRRP announcements pass-through.

Rule definition

VRRP’s announcement multicast packets have the following characteristics:

  1. They are sent to the following multicast IP address: 224.0.0.18
  2. They use the protocol vrrp
  3. They source IP address is a virtual router

Thus, a rule that allows all the incoming VRRP traffic would look like this:

ACCEPT  net fw:224.0.0.18 vrrp

A rule that allows VRRP packets from a specific router would look like this:

ACCEPT  net:OTHER_VIRTUAL_ROUTER_IP fw:224.0.0.18 vrrp

Example

Let’s imagine we have two routers implementing VRRP (using keepalived, for example). Their IPs are: 10.20.30.40 and 10.20.30.41. Their shorewall rules should include the following:

on 10.20.30.40:

ACCEPT  net:10.20.30.41 fw:224.0.0.18 vrrp

on 10.20.30.41:

ACCEPT  net:10.20.30.40 fw:224.0.0.18 vrrp

References

KeepAlived Installation under Debian Etch

Briefly, KeepAlived is a daemon that is able to provide failover capabilities to servers/services by binding virtual IP addresses to machines. In the event of failure, KeepAlived would reassign this virtual IP to another machine. This action is executed fast (less than 2 seconds) and automatically.

This is a very interesting daemon to be used in combination with HAProxy, for example. It would be possible to have a failovered load balancer. In the event of this load balancer failing, keepalived would switch to another that is up and running in such a clean and fast way that the clients would not notice.

Installation steps under Debian Etch

apt-get update
apt-get install keepalived

The system will ask a couple of questions. I usually reply using the default values, then configure myself manually the daemon, by editing /etc/keepalived/keepalived.conf.

To make the virtual IP address bindable, you should add this line /etc/sysctl.conf:

net.ipv4.ip_nonlocal_bind=1

Check binding:

sysctl -p

net.ipv4.ip_nonlocal_bind = 1

It is convenient to alter the order when keepalived is being started upon restarts. We probably want to have it started at the end so all the services are already running by the time keepalive runs. To do that:

update-rc.d -f keepalived remove
Removing any system startup links for /etc/init.d/keepalived ...
/etc/rc0.d/K20keepalived
/etc/rc1.d/K20keepalived
/etc/rc2.d/S20keepalived
/etc/rc3.d/S20keepalived
/etc/rc4.d/S20keepalived
/etc/rc5.d/S20keepalived
/etc/rc6.d/K20keepalived

update-rc.d keepalived defaults 90
Adding system startup for /etc/init.d/keepalived ...
/etc/rc0.d/K90keepalived -> ../init.d/keepalived
/etc/rc1.d/K90keepalived -> ../init.d/keepalived
/etc/rc6.d/K90keepalived -> ../init.d/keepalived
/etc/rc2.d/S90keepalived -> ../init.d/keepalived
/etc/rc3.d/S90keepalived -> ../init.d/keepalived
/etc/rc4.d/S90keepalived -> ../init.d/keepalived
/etc/rc5.d/S90keepalived -> ../init.d/keepalived

See Also

Having HAProxy check mysql status through a xinetd script

HAProxy is able to load balance MySQL wonderfully. The main issue is how to make sure that the backend MySQL server to forward the request to is up and running (I mean not just to establish a connection to port 3306, I mean something more “complete”, that performs a little operation against the MySQL server).

It is possible to make haproxy check the status of a mysql server using a small shell script managed through the xinetd daemon.

What this script basically does is performs a basic operation against the mysql database then returns http status 200 if the operation was successful or http status 500 if it there was any error (i.e. mysql was not available).

Script

The script looks like this:

#!/bin/bash
#
# This script checks if a mysql server is healthy running on localhost. It will
# return:
#
# "HTTP/1.x 200 OKr" (if mysql is running smoothly)
#
# - OR -
#
# "HTTP/1.x 500 Internal Server Errorr" (else)
#
# The purpose of this script is make haproxy capable of monitoring mysql properly
#
# Author: Unai Rodriguez
#
# It is recommended that a low-privileged-mysql user is created to be used by
# this script. Something like this:
#
# mysql> GRANT SELECT on mysql.* TO 'mysqlchkusr'@'localhost' 
#     -> IDENTIFIED BY '257retfg2uysg218' WITH GRANT OPTION;
# mysql> flush privileges;

MYSQL_HOST="localhost"
MYSQL_PORT="3306"
MYSQL_USERNAME="mysqlchkusr"
MYSQL_PASSWORD="secret"

TMP_FILE="/tmp/mysqlchk.out"
ERR_FILE="/tmp/mysqlchk.err"

#
# We perform a simple query that should return a few results :-p
#
/usr/bin/mysql --host=$MYSQL_HOST --port=$MYSQL_PORT --user=$MYSQL_USERNAME 
	--password=$MYSQL_PASSWORD -e"show databases;" > $TMP_FILE 2> $ERR_FILE

#
# Check the output. If it is not empty then everything is fine and we return
# something. Else, we just do not return anything.
#
if [ "$(/bin/cat $TMP_FILE)" != "" ]
then
	# mysql is fine, return http 200
	/bin/echo -e "HTTP/1.1 200 OKrn"
	/bin/echo -e "Content-Type: Content-Type: text/plainrn"
	/bin/echo -e "rn"
	/bin/echo -e "MySQL is running.rn"
	/bin/echo -e "rn"
else
	# mysql is fine, return http 503
	/bin/echo -e "HTTP/1.1 503 Service Unavailablern"
	/bin/echo -e "Content-Type: Content-Type: text/plainrn"
	/bin/echo -e "rn"
	/bin/echo -e "MySQL is *down*.rn"
	/bin/echo -e "rn"
fi

Steps on the MySQL server

First, you should create the script somewhere, and assign proper permissions:

chown nobody /opt//mysqlchk
chmod   744  /opt//mysqlchk

Then, set permissions into the mysql server:

mysql> GRANT SELECT on mysql.* TO 'mysqlchkusr'@'localhost' 
    -> IDENTIFIED BY 'secret' WITH GRANT OPTION;
mysql> flush privileges;
mysql> exit

Test:

/opt/mysqlchk
HTTP/1.x 200 OK

Now, configure xinetd by adding this line at the bottom of /etc/services:

mysqlchk        9200/tcp                        # mysqlchk

Then add this file /etc/xinetd.d/mysqlchk:

# default: on
# description: mysqlchk
service mysqlchk
{
        flags           = REUSE
        socket_type     = stream
        port            = 9200
        wait            = no
        user            = nobody
        server          = /opt/mysqlchk
        log_on_failure  += USERID
        disable         = no
        only_from       = 0.0.0.0/0 # recommended to put the IPs that need
                                    # to connect exclusively (security purposes)
        per_source      = UNLIMITED # Recently added (May 20, 2010)
                                    # Prevents the system from complaining
                                    # about having too many connections open from
                                    # the same IP. More info:
                                    # http://www.linuxfocus.org/English/November2000/article175.shtml
}

Restart xinetd (you can watch for issues on /var/log/syslog):

/etc/init.d/xinetd stop
/etc/init.d/xinetd start

Test:

telnet localhost 9200
Trying 127.0.0.1...
Connected to localhost.localdomain.
Escape character is '^]'.
HTTP/1.1 200 OK

Content-Type: Content-Type: text/plain

MySQL is running.

Connection closed by foreign host.

Steps on the HAProxy server
Now, in order to make haproxy check the status of the mysql service through the xinetd-managed-script, we should add something similar to this on the haproxy.cfg file:

listen  MySQL 10.135.2.67:3306
        mode    tcp
	option  httpchk
        server  10.135.2.69:3306 10.135.2.69:3306 check port 9200 inter 12000 rise 3 fall 3
        source  10.135.2.67

What is important?

  1. option httpchk.- tells haproxy to check for full http response (i.e. http headers: 2xx OK or 5xx ERROR)
  2. check port XXXX.- tells haproxy to check the status of the service by sending an http request on that port