LiveConfig & DRBD

Category: LiveConfig
Created: 2020-12-09

These instructions describe what you have to consider when configuring a high availability environment with DRBD (linux-ha) and LiveConfig.

LiveConfig (general)

The following files/directories should be mirrored on the secondary nodes via DRBD:

/etc/liveconfig/ (configuration files, license key, Lua customizations)
/var/lib/liveconfig/ (runtime data)

Usually /etc/ is not on a DRBD volume. In addition, the configuration files must also be available on an inactive secondary server, otherwise package updates won’t work. Since the data in /etc/liveconfig/ rarely changes, a simple solution would be if the primary node regularly copies this data to a DRBD volume, and the secondary (the “future” primary) copies these files back locally to /etc/liveconfig/ in case of a failover.

With an active-passive cluster like DRBD, one active LiveConfig license is sufficient. As long as LiveConfig is active on only one of the cluster servers, it does not have to be licensed separately on the standby servers.

The LiveConfig service (whether liveconfig or lcclient) should be switched over at the very end of the failover (after all other services).

LiveConfig Server

If possible, use LiveConfig in a DRBD cluster with a MySQL or MariaDB database.

If you use LiveConfig with the integrated SQLite database, the directory /var/lib/liveconfig/ must be on the DRBD volume. A regular rsync of these files is no longer sufficient.

Services

The failover configuration of the individual services (apache2, postfix, dovecot, etc.) does not differ from an installation without LiveConfig, so there are no special features to consider.

Configuration files should ideally not refer to a DRBD volume individually as a symlink, but the respective directory should be a symlink. When updating configuration files, LiveConfig usually creates a new file and renames it at the end - file symlinks do not work with this.