We have a kind of strange problem.
We used to have a quite simple Webb structure with just One Proxy -> One Varnish Frontend – > One Drupal Webb server and with One Memcache on the same server. Since this was not an ideal solution we decided to expand.
The new solution recommended by many was a loadbalancer (f5) -> a cluster with 2 Vanish front servers-> a cluster of 2 Drupal servers (Memcache on each server) -> a cluster of 2 My Sql (Maria) Databases. We build it up, everything looked fine during test, but now we have run into problems.
What actually happend was that users (publishers) started to update content, but after editing content/saving, and then they logged out from Drupal’s CM tool. They often couldn’t see the their changes on on their actual page. We tracked their sessions and figured out that after some minutes their session cookies were gone… and that their content actually was saved on Drupal server 1 and in the database cluster. But after logging out and logging in next time. they were directed to 2nd Drupal server and there they couldn’t find their content…?? We don’t understand why the 2nd Drupal Server never got the content from the database…
We even tested with setting Memcache first one and then both off, but even so…the problems still was there…
The temporary solution was to close down 1 Varnish front and 1 Drupal server, and now it works again…
But this is a just a short term solution as we need to scale up due to redundancy and upcoming dev projects.
If anyone has faced this problems before we would be more then happy to here how you solved it?
Some technical information, users login in to Drupal CM with their AD users account, connect to Shibboleth.
Everything in on NFS discs.