Chapter 11. Running a NetBoot Server

Setting the stage for Macworld Expo 1999, then-interim CEO Steve Jobs rolls out a huge rack of some 50 iMacsall fully operational (one with a dead video card) and playing the same movie file without a single hard disk among them. However, Steve wasn't introducing the iMac, because it was old news by that time; he was introducing the first commercially available Mac OS X system. All the iMacs started up from a single copy of an operating system being hosted by a Mac OS X Server. That's right: One of the first public demonstrations of the future technology to drive all new Apple computers was a Mac OS X Server running the NetBoot service.

A server running the NetBoot service shares disk image files that contain the system software. Client computers, when instructed, automatically find and start up from any one of these disk images across the network. On a fast server with Gigabit Ethernet, more than 50 clients can start up from one disk image. Once booted, a client acts like any other computer that has been started from a local volume. Any changes made to the NetBoot client computer while running are lost upon restart, ensuring consistent system software across all your computers.

However, starting up over the network is only the tip of this iceberg. It's important to realize that an administrator can use the NetBoot service for a variety of time-saving administration techniques. For example, a special type of boot image, dubbed an install image, can be used to facilitate rapid mass deployment across your network. After you start up a computer, the install image can then automatically install onto the local volume all the software required for your system build. Another potential use for NetBoot is to create an image that contains all your favorite system maintenance and repair utilities. You can configure the ultimate administrator's toolkit, which is available to any computer on your network at any timewithout having to carry a single CD or FireWire disk! The sky is the limit, because the NetBoot service is highly scalable. Each server can host 25 different images, and you can use as many NetBoot servers as you need on your network. NetBoot servers will even automatically load-balance traffic for high-demand images if the same image is on multiple servers.

Upon further dissection, NetBoot is a combination of several different protocols, all working in concert to facilitate the remote booting of an operating system over the network. The services required to provide NetBoot include Dynamic Host Configuration Protocol (DHCP) to provide initial IP addressing information, Boot Service Discovery Protocol (BSDP) to advertise the location of the NetBoot server, Trivial File Transfer Protocol (TFTP) to deliver the initial boot files, and either Network File System (NFS) or Web services via HyperText Transfer Protocol (HTTP) to mount the system boot image. On the client side, the Open Firmware instructions built into the hardware of every modern Apple computer facilitate the NetBoot startup process.