How to upgrade a clustered environment

The upgrade in a clustered environment works nearly the same as in a non-clustered as described in the official documentation.

A general note: it is not possible to use the instance while the upgrade is happening, but the upgrade should be a matter of a few minutes usually.

You should follow some steps:

  • (optional) serve via the load balancer a static maintenance page with more information - otherwise the default "Instance is in maintenance mode" page will be shown, which should also be fine
  • enable maintenance mode (this is stored in the config.php - so if you have them on a shared storage it only needs to be done on one server and the others should receive this as well - otherwise do it on every web server) -┬áin practice it is helpful to just shut down the web server of each node except the one that handles the upgrade
  • disable cron.php execution (it doesn't start new jobs while in maintenance, but maybe there is one running)
  • the web based updater is not suited for a clustered environm

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