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Getting Started with Linux-HA (heartbeat) Intro Let me preface this document by saying most of this is _not_ original work. My purpose for writing this document is just trying to contribute in some way to possibly help those who REALLY get things done. The "work" I am contributing is mostly compiling bits and pieces from other HA documents (such as Volker Wiegand's Hardware Installation Guide) into a document that can help novices get started on HA without pestering Alan (like I did!) and to cut down on repeat questions on the mailing list. Getting Started The first thing you'll need is two computers. You need not have identical hardware in both machines (or amount of memory, etc.), but if you did, it would make your life that much easier when a component fails. Now you have to decide on some of your implementation. Your "cluster" is established via a "heartbeat" between the two computers (nodes) generated by the software package of the same name. However, this heartbeat needs one or more media paths (serial via a null modem cable, ethernet via a crossover cable, etc.) between the nodes. At this point, you're actually ready to begin hardware-wise. Of course, since you're looking into HA, you'll mostly likely want to avoid having only one point of failure. In this case, that would be your null modem cable/serial port or network interface card(NIC)/crossover cable. So, you need to decide whether you wish to add a second serial/null modem connection or a second network interface card (NIC)/crossover connnection to each node. See Appendix A for instructions on how to build a Cat-5 crossover cable. My heartbeat path setup uses one serial port and one extra NIC because I only had one null modem cable, had an extra of NIC on hand and thought it was good to have two medium types for the heartbeats. Once your hardware is in order, you must install your OS and configure your networking (I used Red Hat). Assuming you have 2 NICs, one should be configured for your "normal" network and the other as a private network between your clustered nodes (via the crossover cable). For an example, we will assume that our cluster will have the following addresses: Node 1 (linuxha1): 192.168.85.1 (normal 192x net) 10.0.0.1 (private 10x net for heartbeat) Node 2 (linuxha2): 192.168.85.2 (192x) 10.0.0.2 (10x) Note: None of these addresses should be your "cluster address" - the address handled by heartbeat and failed over between nodes! Most *nix distributions this easy during installation, however, if you are having any problems, refer to either the Ethernet HOWTO, or the documentation for your distribution. To check your configuration, type: ifconfig This will show your network interfaces and their configuration. You can obtain your network routing information from "netstat -nr". If it looks good, make sure you can ping between both nodes on all interfaces. Next, if you're using one, you'll need to test your serial connection. On one node, which will be the receiver, type: cat </dev/ttyS0 On the other node, type,: echo hello >/dev/ttyS0 You should see the text on the receiver node. If it works, change their roles and try again. If it doesn't, it may be as simple as having the wrong device file. Volker's HA Hardware Guide and the Serial HOWTO are two good resources for troubleshooting your serial connection. Installing Heartbeat. You can now install the heartbeat package. If you're reading this, you already have it, but in any case it's available at: [1]http://linux-ha.org/download There are binary RPMs at the website, or you can build heartbeat from source. Grab the tarball (or install the source RPM). Untar it into your favorite source directory. From the top of the source tree, type "./ConfigureMe configure", followed by "make" and "make install". If you have problems installing the RPMs found at the website and want a way to make your own, there may be help in the [2]FAQ. Configuring Heartbeat Configuring ha.cf There are three files you will need to configure before starting up heartbeat. First, is ha.cf. This will be placed in the /etc/ha.d directory that is created after installation. It tells heartbeat what types of media paths to use and how to configure them. The ha.cf in the source directory contains all the various options you can use, I'll go through it line by line... serial /dev/ttyS0 Use a serial heartbeat - if you don't use a serial heartbeat, you must use another medium, such as a bcast (ethernet) heartbeat. Replace /dev/ttyS0 with the appropriate device file for your required serial heartbeat. watchdog /dev/watchdog Optional. The watchdog function provides a way to have a system that is still minimally functioning, but not providing a heartbeat, reboot itself after a minute of being sick. This could help to avoid a scenario where the machine recovers its heartbeat after being pronounced dead. If that happened and a disk mount failed over, you could have two nodes mounting a disk simultaneously. If you wish to use this feature, then in addition to this line, you will need to load the "softdog" kernel module and create the actual device file. To do this, first type "insmod softdog" to load the module. Then, type "grep misc /proc/devices" and note the number it reports (should be 10). Next, type "cat /proc/misc | grep watchdog" and note that number (should be 130). Now you can create the device file with that info typing, "mknod /dev/watchdog c 10 130". bcast eth1 Specifies to use a broadcast heartbeat over the eth1 interface (replace with eth0, eth2, or whatever you use). keepalive 2 Sets the time between heartbeats to 2 seconds. warntime 10 Time in seconds before issuing a "late heartbeat" warning in the logs. deadtime 30 Node is pronounced dead after 30 seconds. initdead 120 With some configurations, the network takes some time to start working after a reboot. This is a separate "deadtime" to handle that case. It should be at least twice the normal deadtime. hopfudge 1 Optional. For ring topologies, number of hops allowed in addition to the number of nodes in the cluster. baud 19200 Speed at which to run the serial line (bps). udpport 694 Use port number 694 for bcast or ucast communication. This is the default, and the official IANA registered port number. auto_failback on Required. For those familiar with Tru64 Unix, heartbeat acts as if in "favored member" mode. The master listed in the haresources file holds all the resources until a failover, at which time the slave takes over. When auto_failback is set to on once the master comes back online, it will take everything back from the slave. When set to off this option will prevent the master node from re-acquiring cluster resources after a failover. This option is similar to to the obsolete nice_failback option. If you want to upgrade from a cluster which had nice_failback set off, to this or later versions, special considerations apply in order to want to avoid requiring a flash cut. Please see the [3]FAQ for details on how to deal with this situation. node linuxha1.linux-ha.org Mandatory.