An article at RTC Magazine by John Mehaffey of MontaVista discusses runtime application patching, a method of modifying running applications on systems that can not be restarted due to availability requirements. The technique can be used to upgrade software, fix bugs, or even to temporarily add debugging routines.

Runtime patching would typically be done on Carrier Grade systems expected to provide “five nines” of uptime; in other words, to be available 99.999% of the time, or have less than five minutes of downtime per year.

The technique allows patches to be tried out and then removed if unintended consequences emerge without the need to restore from a backup, which would result in a loss of interim data. It obviates the potential for catastrophic device failure that can strike when parts of a redundant system are brought down and patched separately. And, it provides an effective way to debug a running production system, according to Mehaffey.

The article presents an overview of the technique, with some advice about how to perform the operation effectively.

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