Getting Started with Heartbeat
The third configuration file is the haresources file. Before configuring it, you need to do some housecleaning. Namely, all services that you want Heartbeat to manage must be removed from the system init for all init levels.
On Debian-style distributions, the command is:
/usr/sbin/update-rc.d -f <service_name> remove
Check your distribution's documentation for how to do the same on your nodes.
Now, you can put the services into the haresources file. As with the other two configuration files for Heartbeat, this one probably won't be very large. Similar to the authkeys file, the haresources file must be exactly the same on every node. And, like the ha.cf file, position is very important in this file. When control is transferred to a node, the resources listed in the haresources file are started left to right, and when control is transfered to a different node, the resources are stopped right to left. Here's the basic format:
<node_name> <resource_1> <resource_2> <resource_3> . . .
The node_name is the node you want to be the primary on initial startup of the cluster, and if you turned on auto_failback, this server always will become the primary node whenever it is up. The node name must match the name of one of the nodes listed in the ha.cf file.
Resources are scripts located either in /etc/ha.d/resource.d/ or /etc/init.d/, and if you want to create your own resource scripts, they should conform to LSB-style init scripts like those found in /etc/init.d/. Some of the scripts in the resource.d folder can take arguments, which you can pass using a :: on the resource line. For example, the IPAddr script sets the cluster IP address, which you specify like so:
In the above example, the IPAddr resource is told to set up a cluster IP address of 192.168.1.9 with a 24-bit subnet mask (255.255.255.0) and to bind it to eth0. You can pass other options as well; check the example haresources file that ships with Heartbeat for more information.
Another common resource is Filesystem. This resource is for mounting shared filesystems. Here is an example:
The arguments to the Filesystem resource in the example above are, left to right, the device node (an ATA-over-Ethernet drive in this case), a mountpoint (/opt/data) and the filesystem type (xfs).
For regular init scripts in /etc/init.d/, simply enter them by name. As long as they can be started with start and stopped with stop, there is a good chance that they will work.
Listings 4 and 5 are haresources files for two of the clusters I run. They are paired with the ha.cf files in Listings 2 and 3, respectively.
Listing 5. A More Substantial haresources File
deimos \ IPaddr::192.168.12.1 \ Filesystem::/dev/etherd/e1.0::/opt/storage::xfs \ killnfsd \ nfs-common \ nfs-kernel-server
The cluster defined in Listings 2 and 4 is very simple, and it has only two resources—a cluster IP address and the Apache 2 Web server. I use this for my personal home Web server cluster. The servers themselves are nothing special—an old PIII tower and a cast-off laptop. The content on the servers is static HTML, and the content is kept in sync with an hourly rsync cron job. I don't trust either “server” very much, but with Heartbeat, I have never had an outage longer than half a second—not bad for two old castaways.
The cluster defined in Listings 3 and 5 is a bit more complicated. This is the NFS cluster I administer at work. This cluster utilizes shared storage in the form of a pair of Coraid SR1521 ATA-over-Ethernet drive arrays, two NFS appliances (also from Coraid) and a STONITH device. STONITH is important for this cluster, because in the event of a failure, I need to be sure that the other device is really dead before mounting the shared storage on the other node. There are five resources managed in this cluster, and to keep the line in haresources from getting too long to be readable, I break it up with line-continuation slashes. If the primary cluster member is having trouble, the secondary cluster kills the primary, takes over the IP address, mounts the shared storage and then starts up NFS. With this cluster, instead of having maintenance issues or other outages lasting several minutes to an hour (or more), outages now don't last beyond a second or two. I can live with that.
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- The Usability of GNOME
- Linux for Astronomers
- Multitenant Sites
- PostgreSQL, the NoSQL Database