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Cache related problems when accessing websites from Citrix environment

View profile for Andrew Gray
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Citrix is popular with law firms in the UK - particularly its products that provide virtualisation services. Citrix users don't normally experience any difficulty using their preferred browser to access websites. However, from time to time our clients report strange behaviour that seem to be associated with some aggressive caching behavour on the part of Citrix.

Problems are rare, but when they do occur a typical scenario is that an Editor changes the content of a web page but then fails to see the result of their efforts even though the change is visible to the rest of the internet. The reason for this appears to be that, in some installations, Citrix decides to cache the unedited version of the page and ignores the HTTP header request not to do so.

Most people are familiar with the fact that their browsers will cache content (e.g. to avoid having to download the same logo.jpg on every page request), but people are less familiar with the idea that other devices in the network might also be deciding to cache content. When accessing a website from within a Citrix environment it's clear that Citrix does indeed get deeply involved in the process as outlined in this article. Each and every HTTP response that is sent contains HEADER information that is designed to tell any cache device whether or not to cache the request (and if so, for how long). When a device decides to cache something even though it is being told not it this can sometimes cause a problem as was the case in the scenario described above.

We have lots of clients using Citrix and only a few have suffered in this way. If you dig into Citrix deeply enough then you can control how aggressively it caches things - and most of our clients have managed to find someone familiar enough with Citrix to be able to do just that - problem solved.

If you are in any doubt as to whether your strange behaviour is related to Citrix, you obviously need to repeat your activity on a machine that is accessing the internet directly (rather than from Citrix). For the best possible test you should try to use the same machine (and the same browser).

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