The Uninterruptible Power Supply Imperative
Power failures, spikes, supply surges and brown-outs remain a fact of life - as do the service disruptions, data corruption, mangled file systems and hardware damage that result from such power interruptions in the data center, server rooms and other ICT facilities. So the entire community of ICT professionals has begun to understand electricity, the threats it can bring, and the imperative of using supplementary devices to shield critical ICT infrastructure.
The Uninterruptible Power Supply (UPS) is such a device. The UPS maintains a continuous supply of electric power to connected equipment by supplying power from a separate source when utility power is disrupted. Its rechargeable batteries supply emergency power in the event of power loss and if the power loss is extensive the UPS can signal to initiate an orderly power down sequence. UPSs come in sizes ranging from units which will back up a single computer to units which will power entire data centers or buildings.
| Most UPS models have a serial or USB console port to allow other devices to monitor their status, and they come with client software that provides basic management. Larger enterprise UPSs are more complex with multiple communication ports or network ports with SNMP reporting, and they allow multiple servers to monitor the power status and often provide tracking over time of attributes such as temperature and voltage.
It is imperative that the UPSes are monitored closely as each UPS will only provide power for a limited period of time (often only 10-15mins) and the system administrators must be given time to perform graceful (and generally unattended) shutdowns. In a typical rack mount site you will have complex architecture with a large number of servers and network devices (often dual powered) being supplied by multiple UPSes, and across the site these UPSes will often have been sourced from multiple vendors. So the software tools each vendor provides may not deliver an adequate monitoring and management solution. |
The Network UPS Tools (NUT)
Network UPS Tools (NUT) is a group of open source programs that provide a common interface for monitoring and administering UPS hardware; and ensuring safe shutdowns of the systems which are connected. NUT is built on a networked model with a layered scheme of drivers, server and clients:
- The driver programs talk directly to the UPS equipment and run on the same host as the NUT network server (upsd). Drivers are provided for a wide assortment of equipment from most of the popular UPS vendors and they understand the specific language of each UPS and map it back to a compatibility layer. This means both an expensive "smart" protocol UPS and a simple "power strip" model can be handled transparently.
- The NUT network server program upsd is responsible for passing status data from the drivers to the client programs via the network. upsd can cache the status from multiple UPSes and then serve this status data to many clients. upsd also contains access control features to limit the abilities of the clients (e.g. so only authorized hosts may monitor or control the UPS hardware)
- There are a number of NUT clients that connect to upsd to check on the status of the UPS hardware and do things based on the status. These clients can run on the same host as the NUT server or they can communicate with the NUT server over the network (enabling them to monitor any UPS anywhere). The upsmon client enables servers that draw power through the UPS to shutdown gracefully when the battery power reaches critical. There are also status/logging clients (upsc and upslog) and third party interface clients.
This layered NUT architecture enables:
- Multiple manufacturer support: NUT can monitor USB models from 79 different manufacturers with a unified interface
- Multiple architecture support: NUT can manage serial and USB connected USB models with the same common interface. Network connected USB equipment can also be monitored using SNMP
- Multiple clients monitoring the one UPS: Multiple systems may monitor a single UPS using only their network connections and there's a wide selection of client programs which support monitoring UPS hardware via NUT (Big Sister, Cacti, Nagios and more)
Embedded UPS Management
The Network UPS Tools now run in Opengear's console servers. The NUT tools (upsd, upsmon, UPS drivers, upsc) and supporting libraries (libgd, libusb) are embedded in the IM4200, IMG4000 and CM4100 families of console servers. The Opengear web CGI has been extended to support NUT configuration and report UPS status. And the SDT management software has been extended to monitor UPS networks. SDT for Nagios now supports UPS hosts and the new check_ups plugin reports on the status. SDT Connector now invokes a NUT client or NUT status CGI.
The embedded UPS management enables sysadmins to use their console servers to securely monitor and manage their distributed UPS hardware:
- The embedded Network UPS Tools provide reliable monitoring of serial and USB connected UPS hardware, alerts administators of power status changes and ensures the safe shutdown of connected devices
- Should a power event at a remote site disrupt the main network connection the console server can be accessed out of band enabling the remote administrator to retain visibility and control of the power at the site
- UPSes from all the popular vendors including APC, Belkin, MGE, Powerware and Tripp Lite can be monitored using the one simple interface
- In the event of a UPS alert Opengear's central management can execute the appropriate vendors management client (such as LanSafe if it was a Powerware UPS)
