Rebooting servers in a data center takes more than just a push of the power button. Since data center security policies are typically complicated, you'll need a solution for those times when urgent server maintenance must be done but you can't get into the facility quickly enough. Say "hello" to the remote reboot.
Generally, there are two options for rebooting remotely: You can either put a management card in the server or use a solution for remote power management -- a power distribution unit (PDU) for our purposes. While a PDU manages the power supply and nothing else, a management interface card allows you to do much more on your server. Let's take a deeper look at the features to figure out what fits best for you.
Reboot remotely with power management
To provide power to rackmount servers, use integrated PDUs with simple network management protocol capabilities. These PDUs allow administrators to open a telnet session, connect to the PDU and run commands from the telnet interface to shut down a server. This is easy to do, especially if your server only has one power supply.
Many modern servers, however, have redundant power supplies. If the design for your fault-tolerant environment has been executed well, then the supplies are connected not only to one, but two PDUs. This changes the situation for the data center administrator: Instead of opening a telnet session to one PDU, he or she has to communicate to two different PDUs, and this typically is where things can go wrong.
Ideally, if a server needs to be reset, power to both power supplies should be cut simultaneously. That demands a minimal amount of preparation; the administrator first needs to open a telnet session to both PDUs and make sure that the port-specific servers they're connected to reboot simultaneously. Even a difference of a few seconds may result in the servers not being restarted at all because when recycling power on the second power supply, the first power supply may already be up and running again. But if the administrative procedures are well organized, using PDUs for remote reboots is easy.
Management cards present other options
While the PDU remote reboot management solution is basically just an extension of normal power distribution to racks, integrated management cards -- such as Hewlett-Packard's iLO or Dell's Drac --were developed for different purposes. These cards, which work with various brands of servers, allow administrators to connect to a server even if it has crashed. To accomplish this, the management card runs a small OS on its own IP address, which works as long as the card is connected to a power supply. Remote management cards offer an interface to the server that allows administrators to troubleshoot from afar. Rebooting remotely is also just one function of the management card.
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Which remote server management option is best?
To perform a remote reboot, the administrator simply connects to whatever interface the remote management card offers and issues the reboot command. The interface can be simple and Web-based, or a program run on a local workstation. From the interface menu, administrators can perform a wide range of operations beyond the reboot, such as monitoring the current state of the server, opening a console session to work remotely on the server, or performing a power cycle from a distance.
Apart from the management interface, the administrator can also open a telnet session to connect to the management card to perform tasks that don't require a graphical interface, such as resetting a server. Also, some brands have a very extensive scripting language that allows the administrator to run all kinds of scripts on an interface.
Management cards offer an interface from which the administrator can perform a wide range of tasks, including remote reboot.
If you're looking for a way to reboot your server remotely, the management card has one major benefit over PDUs: There is just one card for the entire server regardless of how many power supplies are installed. The disadvantage is that some servers don't have a management card enabled by default, which means that you have to make an additional investment to use the card. In cases where you simply need an option to reset your servers from a distance, a rack PDU is a good choice, but make sure you handle the issues that could arise when servers have redundant power supplies installed.
ABOUT THE AUTHOR: Sander van Vugt is an independent trainer and consultant based in the Netherlands. He is an expert in Linux high availability, virtualization and performance, and has completed several projects that implement all three. He is also the writer of various Linux-related books, such as Beginning the Linux Command Line, Beginning Ubuntu Server Administration and Pro Ubuntu Server Administration.