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12.3 Components of a High
A high availability solution consists of several different components:
General Infrastructure
When designing a high availability solution, it should generallxy be remembered
that even the installation of all key servers at a single location can be a potential
SPOF if this location is hit by disaster or power failures. The environmental condi-
tions of the servers should also be taken into account—(redundant) air conditioning
systems are essential.
Hardware
Even the most sophisticated software cannot produce a high availability system
without the greatest possible security from failure on a hardware level. The key
hardware components that should be considered and laid out with the greatest
possible redundancy are:
Power Supply
Network Interfaces
Hard Disks
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Installation and Administration
Availability Solution
If possible, secure your servers using a UPS (uninterruptible power supply) to
ensure that a brief power failure can be bridged and the systems can be shut
down correctly in the event of a longer power failure. The power supply should
also be configured for redundancy.
Make sure each of your systems has several network interfaces. If one interface
fails, another must automatically take over the address and task of the failed
component. Redundancy expressly relates to the two interface directions. There
is no harm planning an active and backup interface for both the internal and
external interfaces.
Assign several hard disks to your system and arrange the data backup (e.g.,
using RAID or drbd) in such a way that if one of these disks is lost, the others
always contain the intact data record. It must be possible to replace a faulty
disk with a new one without stopping the system.
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