how to guide: performance and agility
This prevents functions that optimise the performance of the web application from also being ‘offloaded’.
Optimised experience The ability to determine what kind of device a user is accessing the site from allows the web server to serve content that is appropriate for that device. Not only does this optimise the user’s experience of the site, it can also alleviate some of the workload for the web server. For example, if a user is accessing the site from a mobile device, it suits both user and web server not to load up large images. Just as offloading security functions
improves the performance of a web server, web application optimisation functions are also best handled outside the server (but still behind the firewall). However, if all data is encrypted at the point of entry to/exit from the server, it is not possible for an external system to inspect that data to see, for instance, what device is being used. This is the argument for using external
appliances that handle security and web application optimisation functions for multiple web servers.
The added benefit of this approach is one
of agility. If an organisation is expecting a peak of traffic, it might spin up a few more virtual web server instances on a single machine. There comes a point, however,
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when the increase in traffic outstrips either the capacity of the machine itself or, if it is installed with an HSM card, the capacity of that card. At this point, the organisation has
to make another trade-off – between maintaining the performance and availability of the site and the cost in man-hours of setting up a new machine and HSM card. If security and optimisation functions are being supported by an external appliance, however, those functions can be called as discrete services by each individual virtual web server. That means the organisation can spin up
new instances quickly and cheaply, removing the need to compromise performance.
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