Load Balance Apache with Highly Available Load Balancer Using Just Two Servers 2


My objective was to have two apache web servers that were load balanced, but I didn’t want to have a single point of failure load balancer and I didn’t want to spend the resources of two more servers solely for a highly available load balancer.  So I combined to run the load balancers on the same two servers running apache.  Of course if you have a high traffic site this is probably not the best solution for you, but if your traffic is moderate this allows you to at least reboot a web server with out taking down your site.

There are several tutorials out there on the subject, but none of them completely solved my challenge.  I’m by no means an expert on this, but I’ve gathered the bits and pieces from the other tutorials to make this work.

This is NOT creating an active/passive Apache cluster. We are creating an active/passive Load Balancer cluster pointing to two independent Apache web servers that just happen to reside on the same servers.

Here’s my setup:

OS:  CentOS 5.5 x64
Virtual IP:  192.168.0.40
Server1:  web01.example.com 192.168.0.41
Server2:  web02.example.com 192.168.0.42

Start with Server1 and install the necessary packages

yum install httpd heartbeat heartbeat-ldirectord

After several tests, I found that heartbeat would always fail on the first attempt to install. I’m not sure if this is specific to CentOS 5.5 x64 or if it also happens on previous releases. Yum would say the install was successful but if you scroll up you would see this:

useradd: user hacluster exists
error: %pre(heartbeat-2.1.3-3.el5.centos.x86_64) scriptlet failed, exit status 9
error:   install: %pre scriptlet failed (2), skipping heartbeat-2.1.3-3.el5.centos

None the less if I try and install heartbeat a second time it always worked.

yum install heartbeat

Set the services to start automatically

chkconfig httpd on
chkconfig heartbeat on
chkconfig ldirectord on

Other tutorials would now instruct you to create an interface eth0:0 but the heartbeat service takes care of this for you.

Configure apache

Start Apache

service httpd start

Since Apache will be accepting connections routed from the load Balancer we have to configure it to handle the virtual IP

Create a second loopback adapter

vim /etc/sysconfig/network-scripts/ifcfg-lo:0

with this content

DEVICE=lo:0
IPADDR=192.168.0.40
NETMASK=255.255.255.255
ONBOOT=yes
NAME=loopback

Restart networking

ifup lo:0

Verify the interface is online

ifconfig lo:0
lo:0      Link encap:Local Loopback
          inet addr:192.168.0.40  Mask:255.255.255.255
          UP LOOPBACK RUNNING  MTU:16436  Metric:1

Files need on the webserver

We need to have a file on the web server for the Load Balancer to know the web server is up and running.

create this file

vim /var/www/html/check.txt

with this content

ok

For testing purposes, so that we know which webserver the load balancer is pointing us to, create this file.

vim /var/www/html/index.html

with this content

web01

Configure the Load Balance, ldirectord

The Load Balancer must route traffic from the virtual IP to apache so we must enable routing.

Edit this file

vim /etc/sysctl.conf

Change the 0 to a 1 on this line

net.ipv4.ip_forward = 1

And add these lines

net.ipv4.conf.all.arp_ignore = 1
net.ipv4.conf.eth0.arp_ignore = 1
net.ipv4.conf.all.arp_announce = 2
net.ipv4.conf.eth0.arp_announce = 2

To activate the changes run this:

sysctl -p

create the Load Balancer configuration file

vim /etc/ha.d/ldirectord.cf

With this content:

checktimeout=30
checkinterval=2
autoreload=yes
logfile="/var/log/ldirectord.log"
quiescent=no
virtual=192.168.0.40:80
        real=192.168.0.41:80 gate
        real=192.168.0.42:80 gate
        service=http
        request="/check.txt"
        httpmethod=GET
        receive="ok"
        persistent=100
        scheduler=lblc
        protocol=tcp
        checktype=negotiate

Start the Load Balancer

service ldirectord start

If you get this error then heartbeat failed to install. Install it again.

/etc/init.d/ldirectord: line 33: /etc/ha.d/shellfuncs: No such file or directory

Create the heartbeat service configuration file.

vim /etc/ha.d/ha.cf

With this content (the node names must match the output of uname -n)

logfile /var/log/heartbeat.log
logfacility     local0
keepalive 2
deadtime 10
bcast   eth0
mcast eth0 225.0.0.1 694 1 0
auto_failback off
node web01.example.com
node web02.example.com

Specify what resources we want heartbeat to manage. In this case we want heartbeat to control the virtual IP and the Load Balancer. Unlike other HA resources the Load Balancer will be running on both nodes at the same time, but heartbeat will control which one is the master. Since we are running all the components on just two servers and there has to be an additional loopback IP, lo:0, the same as the virtual IP we must specify where heartbeat will bind this virtual IP or it will fail to come online.

Create this file:

vim /etc/ha.d/haresources

With this content:

web01.example.com ldirectord::ldirectord.cf LVSSyncDaemonSwap::master IPaddr::192.168.0.40/24/eth0/192.168.0.255

Create the authkeys file required by heartbeat

vim /etc/ha.d/authkeys

With this content:

auth 3
3 md5 randomstring

Hearbeat requires that the authkey file be accessible only by root.

chmod 600 /etc/ha.d/authkeys

Start heartbeat.

service heartbeat start

Wait a few moments to give heartbeat time to bring the Virtual IP online.

Verify the Virtual IP is online

ifconfig
eth0      Link encap:Ethernet  HWaddr 00:50:56:AB:00:15
          inet addr:192.168.0.41  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::250:56ff:feab:15/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:9533 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6248 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:9429192 (8.9 MiB)  TX bytes:607896 (593.6 KiB)

eth0:0    Link encap:Ethernet  HWaddr 00:50:56:AB:00:15
          inet addr:192.168.0.40  Bcast:192.168.0.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

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:1510 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1510 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:140430 (137.1 KiB)  TX bytes:140430 (137.1 KiB)

lo:0      Link encap:Local Loopback
          inet addr:192.168.0.40  Mask:255.255.255.255
          UP LOOPBACK RUNNING  MTU:16436  Metric:1

At this point you now have a single node completely configured. You should be able to browse to http://192.168.0.40 and see that it says web01

Additional verification, run the following command

ip addr sh eth0

If you haven’t yet done any of the configuration for web02 you will see this:


2: eth0:  mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:50:56:ab:00:15 brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.41/24 brd 192.168.0.255 scope global eth0
    inet 192.168.0.40/24 brd 192.168.0.255 scope global secondary eth0:0
    inet6 fe80::250:56ff:feab:15/64 scope link
       valid_lft forever preferred_lft forever

You can also use ipvsadm to show the current statistics for ldirectord.

ipvsadm -L -n

Again since we have not configured the second webserver you will see this

IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  192.168.0.40:80 lblc persistent 100
  -> 192.168.0.41:80              Local   1      0          0

Now lets setup or second web server that will also be the second node of our Load Balancer cluster.

Go back and repeat all the same steps for web02. Do not adjust any of the files to be specific for web02 except the index.html page. The haresources file specifies the preferred host so it should still be the same on both servers.

Once you have completed all the steps on web02, test and make sure everything is working.

ipvsadm -L -n

You should now see both web servers

IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  192.168.0.40:80 lblc persistent 100
  -> 192.168.0.42:80              Route   1      0          0
  -> 192.168.0.41:80              Local   1      0          0

Stop apache on web01

service httpd stop

Now browse to 192.168.0.40 and you should see that it says web02.

Restart apache on web01

service httpd start

The load balancer maintains connection state so if you keep refreshing your browser you should continue to get the same web server.

Now you could stop apache on web02 and refresh your browser and you should get web01.

Now lets test the Load Balancer failover. Apache should be running on both servers.

From another server or workstation start a continuous ping to your Virtual IP 192.168.0.40

On web01 stop the heartbeat service

service heartbeat stop

You should see the IP continues to respond.

On web01 check to see if the eth0:0 is still there. It should not.

ifconfig

On web02 check to see if eth0:0 is there. It should be

ifconfig

Refresh your browser and you should still have a connection to the webserver. It may or may not have connected you to a different server this time.

Congratulations! You now have a highly available load balanced web server configuration.


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2 thoughts on “Load Balance Apache with Highly Available Load Balancer Using Just Two Servers

  • lucky

    Hi James,

    How can we know the incoming requests are load-distributed between the servers involved in the cluster 🙂 ? Do you have any way to test this 🙂

    By the way, thank you for the tutorial 🙂

  • getSurreal

    @ Lucky

    I had the name of the web server in the index file of each server so when I connected I could see which server I connected to