Tuesday, 30 December 2008

Invalidating Single Cached Items

Should have RTFM on this one but it was stuck on the board for so long and even F5 support couldn't figure out so I thought I'd post it here.

Sometimes we need to remove content from our CMS which means our app servers will serve up 404s for those requests. But we found that our F5 kept serving content from its stand-in cache for another 24 hours after the max-age had expired. We thought the stand-in cache was only there for when all the nodes in your pool had died so it looks like it's doing a little more than that.

Anyway, sometimes when we remove stuff from 'live' we really want it gone so we searched around and found that you can remove a single item from the F5 cache using a SOAP request to the management interface. The bad news is that you have to provide usernames and passwords in the clear but there's a nice way to get the same effect using invalidation triggers. At the back of Chapter 11 in the Policy Management Guide there's a straightforward example of what to do.

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