Building a Two-Node Linux Cluster with Heartbeat
According to the accompanying documentation, you need to install a second NIC on both nodes and connect them with a cross overcable. Besides the second NIC, a null modem cable connecting the serial (com) ports of each node is mandatory (according to the documentation). I followed the instructions in the documentation and installed everything. However, as I did more tests on the cluster, I found that the null modem cable, crossover cable and the second NIC are optional; they are nice to have but definitely not mandatory.
Configuring Heartbeat is the most important part of the whole installation and must be set up correctly to get your cluster working. Moreover, it should be identical on both nodes. There are three configuration files, all stored under /etc/ha.d: ha.cf, haresource and aythkeys.
debugfile /var/log/ha-debug # # File to write other messages to # logfile /var/log/ha-log # # Facility to use for syslog()/logger # logfacility local0 # # keepalive: how many seconds between heartbeats # keepalive 2 # # deadtime: seconds-to-declare-host-dead # deadtime 10 udpport 694 # # What interfaces to heartbeat over? # udp eth0 # node atm1 node cluster1 # # ------> end of ha.cf
Whatever is not shown above, you can simply leave as it was (all commented out by the #). The last three options are most important:
udp eth0 # node atm1 node cluster1
Unless you have a cross cable, you should use your eth0 (your only NIC) for udp; the two nodes at the end of the above files must be the same as returned by uname -n from each node.
atm1 IPaddr::192.168.1.4 httpd smb dhcpd
This is the only line you need; in the above example, I included httpd, smb and dhcpd. You may add as many dæmons as you want, provided they have the exact same spelling as those dæmons under /etc/rc.d/init.d
You don't need to add anything to this file, but you have to issue the command
chmod 600 /etc/ha.d/authkeys
You may start the dæmon with
service heartbeat start
Once heartbeat is started on both nodes, you will find that the ifconfig from the primary server will return something like:
node1 ifconfig for node1 eth0 Link encap:Ethernet HWaddr 00:60:97:9C:52:28 inet addr:192.168.1.2 Bcast:192.168.1.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:18617 errors:0 dropped:0 overruns:0 frame:0 TX packets:14682 errors:0 dropped:0 overruns:0 carrier:0 collisions:3 txqueuelen:100 Interrupt:10 Base address:0x6800 eth0:0 Link encap:Ethernet HWaddr 00:60:97:9C:52:28 inet addr:192.168.1.4 Bcast:192.168.1.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Interrupt:10 Base address:0x6800 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 UP LOOPBACK RUNNING MTU:3924 Metric:1 RX packets:38 errors:0 dropped:0 overruns:0 frame:0 TX packets:38 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0
When you see the line eth0:0, heartbeat is working, and you can try to access the server by using http://192.168.1.4 and check the log files /var/log/ha-log. Also, check the log file on node2 (192.168.1.3) and try
ps -A | grep dhcpd
and you should find no running dhcpd on node2.
Now, the real HA test. Reboot, and then shut down the primary server (node1: 192.168.1.2). Don't just power down the server; make sure you issue reboot or press CTL-ALT-DEL and wait until everything is shut down properly before you turn off your PC.
Within ten seconds, go to node2 and try ifconfig. If you can get the IP aliasing eth0:0, you are in business and have a working HA two-node cluster.
eth0 Link encap:Ethernet HWaddr 00:60:08:26:B2:A4 inet addr:192.168.1.2 Bcast:192.168.1.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:15673 errors:0 dropped:0 overruns:0 frame:0 TX packets:17550 errors:0 dropped:0 overruns:0 carrier:0 collisions:2 txqueuelen:100 Interrupt:10 Base address:0x6700 eth0:0 Link encap:Ethernet HWaddr 00:60:08:26:B2:A4 inet addr:192.168.1.4 Bcast:192.168.1.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:15673 errors:0 dropped:0 overruns:0 frame:0 TX packets:17550 errors:0 dropped:0 overruns:0 carrier:0 collisions:2 txqueuelen:100 Interrupt:10 Base address:0x6700
You can try
ps -A | grep dhcpd
or you can try to release and renew the IP info on your Win9x workstation, and you should see the new address for the dhcpd server.
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July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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