I got a problem on a running magento site (CE 22.214.171.124), which got the BLOCK_HTML cache regulary invalidated (even without product/categories edit). The website was tested on 2 different environment without constating this caching issue, the main difference is that the final server is, in fact, two servers managed with load-balancing. They're plugged on the same database and got the /var folder and /media folder shared
My question is : is there any file generation outside /var and /var/cache that should be shared between the two servers ? After thinking of the issue, and if it's a consequence of the loadbalancing it should be something about files present on one server, but not the other. If it's not a consequence of the load-balancing i'm lost though.