Rolling changelog execution in clustered mode

It would be possible to execute database changelog entries online in a rolling update setup.

The new mesh instance would execute the changelog and update the database structure in a way that keeps it compatible with older mesh versions which are also part of the cluster.
The new mesh instance tracks operations that may be invoked by older mesh instances. Newly created elements may need to be migrated on-the-fly.
Once the whole cluster has been switched to the new mesh version and no older mesh instance is online: The final changelog step will be executed which removes the compatibility layer from the db.

gentics / mesh-incubator