How To Setup Linux High Availability

To continue from where I’ve left off on my previous post, this time we’ll setup heartbeat to monitor both of our load balancers, thus allowing us to have what one may call high availability/ failover, between both our load balancers. This method can be used on any server you wish, you can for example have Heartbeat monitor mysql, apache or any other server. In this example, we’ll set up Heartbeat to monitor our crossroads load balancer.

Heartbeat is a daemon that provides cluster services to its clients. This allows clients to know about the presence or disappearance of peer processes on other machines and to easily exchange messages and perform other tasks with them.

To setup heartbeat on centOS, just follow these steps (They must be performed on both servers and they are identical, with the exception of the /etc/hosts file), we’re using a 64bit install, adjust the repository as needed, our 2 servers are shown below along with the virtual ip assigned by Heartbeat (only one server at a time will have the vip assigned): — vip —

1. Add epel repository

bash~# rpm -Uvh

2. Add pacemaker/clusterlabs repository

bash~# wget -O /etc/yum.repos.d/pacemaker.repo

3. Install packages

bash~# yum install pacemaker heartbeat resource-agents cluster-glue*

** If the install above fails, make sure there aren’t any i386 packages conflicting. If so, issue the command below and add the line to /etc/yum.conf

bash~# yum erase *.i386 
bash~# vim /etc/yum.conf 

exclude=*.i386 *.i686

4. Find out machine hostname

bash~# uname -n

*** open udp port 694 on firewall on both machines otherwise this won’t work*****

5. Create config files in directory below:

bash~# cd /etc/ha.d/
bash~# vim

logfacility     local0
deadtime 5
warntime 10
initdead 15
udpport 694
bcast eth0
auto_failback on
use_logd yes
bash~# vim haresources IPaddr::
bash~# cp /usr/share/doc/heartbeat-3.0.3/authkeys /etc/ha.d/
bash~# vim authkeys

auth 2
#1 crc
2 sha1 somekeyhere

bash~# chmod 600 authkeys

6. Create ssh key: use the passphrase used in the authkeys file above when creating the key, in this example it is called “somekeyhere” without the quotes.

bash~# ssh-keygen -t dsa

Generating public/private dsa key pair.
Enter file in which to save the key (/root/.ssh/id_dsa):
Enter passphrase (empty for no passphrase): (this should be the passphrase from above --> somekeyhere)
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_dsa.
Your public key has been saved in /root/.ssh/
The key fingerprint is:

7. copy the key to the other server:

bash~# scp .ssh/

8. add entry in /etc/hosts about the other server in case you’re not using a dns server

9. Start heartbeat:

bash~# service heartbeat start

10. Check the virtual ip address has been assigned (eth0:0). Only one of the 2 servers being monitored will have the virtual ip address assigned at a time. This is the whole point, so whenever hertbeat detects one of the servers down, it automatically assigns the virtual ip to the one that’s available.

bash~# ifconfig

eth0      Link encap:Ethernet  HWaddr 00:24:54:d1:f3:5c  
	  inet addr:  Bcast:  Mask:
          inet6 addr: fe80::224:54ff:fed1:f35c/64 Scope:Link
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:6614 errors:0 dropped:0 overruns:0 frame:0
          TX packets:5133 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:6619801 (6.6 MB)  TX bytes:908555 (908.5 KB)

eth0:0    Link encap:Ethernet  HWaddr 00:1b:b1:4e:2a:44  
          inet addr:  Bcast:  Mask:
          inet6 addr: fe80::21b:b1ff:fe4e:2a44/64 Scope:Link
          RX packets:317696 errors:0 dropped:0 overruns:0 frame:788947
          TX packets:123262 errors:18 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:170312782 (170.3 MB)  TX bytes:19448021 (19.4 MB)

11. Make sure heartbeat starts on boot:

bash~# chkconfig --list | grep heartbeat

12. If not listed, add it:

bash~# chkconfig heartbeat on

*** As I mentioned previously, make sure both Heartbeat machines have the same identical configuration files and also an entry about each other in their respective /etc/hosts in case you’re not using a dns server.

And that’s it, you’ve configured your very own linux high availability “cluster”. Thanks for stopping by once again and remember, please share with others, after all, code should be | because code should be free

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