Automated Installation of Large-Scale Linux Networks
We utilized standard procedures in setting up the server configuration. We set up the DNS, NIS, FTP, Apache, time and NFS services. One special consideration was that no two services were provided by a single IP address. Although we had only four actual servers, we relied heavily on IP aliasing to create virtual personalities for each service. This aliasing method provides for transparent shifting of the services from one machine to another in case of a failure, providing some degree of fault tolerance. This approach is in continuation of our previous work on network fault tolerance, reported in Linux Journal, June 2000.
autofs is a kernel-assisted auto-mounter for Linux which allows the system to dynamically mount a file system on demand. It is like using MS Windows, where, when you need to access a floppy drive, you do not have to specifically attach a drive to a mount point. For example, if autofs is configured to auto-mount a CD-ROM at, say, mount point /misc/cd, then every time a CD-ROM is inserted into the drive and the directory is changed to /misc/cd, the CD-ROM will be automatically mounted at this point. If the mount point is not used for a while, it will be automatically unmounted.
autofs was found to be very useful for our scenario. Over the span of one week, we have many different classes coming into the laboratory. Keeping all the user files mounted on each workstation all the time created a lot of server load and network traffic—an inefficient and undesirable situation. We divided the file system into four groups and mounted them individually via autofs rather than hard-binding the NFS servers in the /etc/fstab file. This reduced the server load to a quarter of its original.
To maintain flexibility, we used NIS for the autofs maps. The map auto.master provides information about the mount point of the autofs system, and auto.home gives information about what file system should be mounted and from which server. It was discovered that the autofs does not check for an NIS map if the file /etc/auto.master is present. Hence, to make it work properly, we removed the file /etc/auto.home from all the workstations that were going to employ autofs. To include these maps in the NIS database, select the rule auto.home and auto.master in the NIS Makefile located at /var/yp/.
The following line was added to /etc/auto.master on the server:
/home auto.home --timeout 60
and these lines were added to /etc/auto.home on the server:
#mount point options source host+path g1 -rw,hard,intr nfs1:/home/g1 g2 -rw,hard,intr nfs2:/home/g2to enable building the proper database.
Jahangir Hasan, on the right, has recently graduated from the Department of Electrical Engineering, University of Engineering and Technology, Lahore, Pakistan. He joined the doctoral program in Electrical and Computer Engineering at Purdue University in fall 2000.
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