5 Setting Up Heartbeat

We've just configured Perlbal to listen on the virtual IP address 192.168.0.99, but someone has to tell lb1 and lb2 that they should listen on that IP address. This is done by heartbeat which we install like this:

lb1/lb2:

apt-get install heartbeat

To allow Perlbal to bind to the shared IP address, we add the following line to /etc/sysctl.conf:

vi /etc/sysctl.conf

[...]
net.ipv4.ip_nonlocal_bind=1

... and run:

sysctl -p

Now we have to create three configuration files for heartbeat, /etc/ha.d/authkeys, /etc/ha.d/ha.cf, and /etc/ha.d/haresources. /etc/ha.d/authkeys and /etc/ha.d/haresources must be identical on lb1 and lb2, and /etc/ha.d/ha.cf differs by just one line!

lb1/lb2:

vi /etc/ha.d/authkeys

auth 3
3 md5 somerandomstring

somerandomstring is a password which the two heartbeat daemons on lb1 and lb2 use to authenticate against each other. Use your own string here. You have the choice between three authentication mechanisms. I use md5 as it is the most secure one.

/etc/ha.d/authkeys should be readable by root only, therefore we do this:

lb1/lb2:

chmod 600 /etc/ha.d/authkeys

lb1:

vi /etc/ha.d/ha.cf

#
#       keepalive: how many seconds between heartbeats
#
keepalive 2
#
#       deadtime: seconds-to-declare-host-dead
#
deadtime 10
#
#       What UDP port to use for udp or ppp-udp communication?
#
udpport        694
bcast  eth0
mcast eth0 225.0.0.1 694 1 0
ucast eth0 192.168.0.101
#       What interfaces to heartbeat over?
udp     eth0
#
#       Facility to use for syslog()/logger (alternative to log/debugfile)
#
logfacility     local0
#
#       Tell what machines are in the cluster
#       node    nodename ...    -- must match uname -n
node    lb1.example.com
node    lb2.example.com

Important: As nodenames we must use the output of

uname -n

on lb1 and lb2.

The udpport, bcast, mcast, and ucast options specify how the two heartbeat nodes communicate with each other to find out if the other node is still alive. You can leave the udpport, bcast, and mcast lines as shown above, but in the ucast line it's important that you specify the IP address of the other heartbeat node; in this case it's 192.168.0.101 (lb2.example.com).

On lb2 the file looks pretty much the same, except that the ucast line holds the IP address of lb1:

lb2:

vi /etc/ha.d/ha.cf

#
#       keepalive: how many seconds between heartbeats
#
keepalive 2
#
#       deadtime: seconds-to-declare-host-dead
#
deadtime 10
#
#       What UDP port to use for udp or ppp-udp communication?
#
udpport        694
bcast  eth0
mcast eth0 225.0.0.1 694 1 0
ucast eth0 192.168.0.100
#       What interfaces to heartbeat over?
udp     eth0
#
#       Facility to use for syslog()/logger (alternative to log/debugfile)
#
logfacility     local0
#
#       Tell what machines are in the cluster
#       node    nodename ...    -- must match uname -n
node    lb1.example.com
node    lb2.example.com

lb1/lb2:

vi /etc/ha.d/haresources

lb1.example.com 192.168.0.99

The first word is the output of

uname -n

on lb1, no matter if you create the file on lb1 or lb2! It is followed by our virtual IP address (192.168.0.99 in our example).

Finally we start heartbeat on both load balancers:

lb1/lb2:

/etc/init.d/heartbeat start

Then run:

lb1:

ip addr sh eth0

... and you should find that lb1 is now listening on the shared IP address, too:

lb1:~# ip addr sh eth0
2: eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:0c:29:a5:5b:93 brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.100/24 brd 192.168.0.255 scope global eth0
    inet 192.168.0.99/24 brd 192.168.0.255 scope global secondary eth0:0
    inet6 fe80::20c:29ff:fea5:5b93/64 scope link
       valid_lft forever preferred_lft forever
lb1:~#

You can check this again by running:

ifconfig

lb1:~# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:0C:29:A5:5B:93
          inet addr:192.168.0.100  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fea5:5b93/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:63983 errors:0 dropped:0 overruns:0 frame:0
          TX packets:31480 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:92604963 (88.3 MiB)  TX bytes:2689903 (2.5 MiB)
          Interrupt:177 Base address:0x1400

eth0:0    Link encap:Ethernet  HWaddr 00:0C:29:A5:5B:93
          inet addr:192.168.0.99  Bcast:192.168.0.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:177 Base address:0x1400

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:56 errors:0 dropped:0 overruns:0 frame:0
          TX packets:56 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:3888 (3.7 KiB)  TX bytes:3888 (3.7 KiB)

lb1:~#

As lb2 is the passive load balancer, it should not be listening on the virtual IP address as long as lb1 is up. We can check that with:

lb2:

ip addr sh eth0

The output should look like this:

lb2:~# ip addr sh eth0
2: eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:0c:29:e0:78:92 brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.101/24 brd 192.168.0.255 scope global eth0
    inet6 fe80::20c:29ff:fee0:7892/64 scope link
       valid_lft forever preferred_lft forever
lb2:~#

The output of

ifconfig

shouldn't display the virtual IP address either:

lb2:~# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:0C:29:E0:78:92
          inet addr:192.168.0.101  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fee0:7892/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:75127 errors:0 dropped:0 overruns:0 frame:0
          TX packets:42144 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:109669197 (104.5 MiB)  TX bytes:3393369 (3.2 MiB)
          Interrupt:169 Base address:0x1400

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:56 errors:0 dropped:0 overruns:0 frame:0
          TX packets:56 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:3888 (3.7 KiB)  TX bytes:3888 (3.7 KiB)

lb2:~#

6 Starting Perlbal

Now we can start Perlbal:

lb1/lb2:

perlbal --daemon

Of course, you don't want to start Perlbal manually each time you boot the load balancers. Therefore we open /etc/rc.local...

vi /etc/rc.local

... and add the line /usr/local/bin/perlbal --daemon to it (right before the exit 0 line):

#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.

/usr/local/bin/perlbal --daemon
exit 0

This will make Perlbal start automatically whenever you boot the load balancers.

(To stop Perlbal, run

killall perlbal

)

7 Testing

Our high-availability load balancer is now up and running.

You can now make HTTP requests to the virtual IP address 192.168.0.99 (or to any domain/hostname that is pointing to the virtual IP address), and you should get content from the backend web servers.

You can test its high-availability/failover capabilities by switching off one backend web server - the load balancer should then redirect all requests to the remaining backend web server. Afterwards, switch off the active load balancer (lb1) - lb2 should take over immediately. You can check that by running:

lb2:

ip addr sh eth0

You should now see the virtual IP address in the output on lb2:

lb2:~# ip addr sh eth0
2: eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:0c:29:e0:78:92 brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.101/24 brd 192.168.0.255 scope global eth0
    inet 192.168.0.99/24 brd 192.168.0.255 scope global secondary eth0:0
    inet6 fe80::20c:29ff:fee0:7892/64 scope link
       valid_lft forever preferred_lft forever
lb2:~#

The same goes for the output of

ifconfig

When lb1 comes up again, it will take over the master role again.

8 Virtual Host Support In Perlbal

Perlbal suppports virtual hosts. Let's assume we want requests for *.site.com to be served by the hosts with the IP addresses 192.168.0.102 and 192.168.0.103, and requests for *.example.com by the hosts 192.168.0.104 and 192.168.0.105. This is how /etc/perlbal/perlbal.conf would look:

vi /etc/perlbal/perlbal.conf

LOAD vhosts

CREATE POOL webfarm1
  POOL webfarm1 ADD 192.168.0.102:80
  POOL webfarm1 ADD 192.168.0.103:80

CREATE SERVICE balancer1
  SET role            = reverse_proxy
  SET pool            = webfarm1
  SET persist_client  = on
  SET persist_backend = on
  SET verify_backend  = on
ENABLE balancer1

CREATE POOL webfarm2
  POOL webfarm2 ADD 192.168.0.104:80
  POOL webfarm2 ADD 192.168.0.105:80

CREATE SERVICE balancer2
  SET role            = reverse_proxy
  SET pool            = webfarm2
  SET persist_client  = on
  SET persist_backend = on
  SET verify_backend  = on
ENABLE balancer2

CREATE SERVICE vdemo
  SET listen         = 192.168.0.99:80
  SET role           = selector
  SET plugins        = vhosts
  SET persist_client = on

  VHOST *.site.com     = balancer1
  VHOST *.example.com  = balancer2
ENABLE vdemo

9 Links

• Perlbal: http://www.danga.com/perlbal/
• Heartbeat: http://www.linux-ha.org/Heartbeat
• Debian: http://www.debian.org