Migrating cubicweb instances - benefits from a distributed architecture

Aim : do the migration for N cubicweb instances hosted on a server to another with no downtime.

Prerequisites : have an explicit definition of the database host (not default or localhost). In our case, the database is hosted on another host. You are not migrating your pyro server. You are not using multisource (more documentation on that soon).

Steps :

1. on new machine : install your environment (pseudocode)

   apt-get install cubicweb cubicweb-applications apache2

2. on old machine : copy your cubicweb and apache configuration to the new machine

   scp /etc/cubicweb.d/ newmachine:/etc/cubicweb.d/
   scp /etc/apache2/sites-available/ newmachine:/etc/apache2/sites-available/

3. on new machine : give new ids to pyro registration so the new instances can register

   cd /etc/cubicweb.d/ ; sed -i.bck 's/^pyro-instance-id=.*$/\02/' */all-in-one.conf

4. on new machine : start your instances

   cubicweb start

5. on new machine : enable sites and modules for apache and start it, test it using by modifying your /etc/host file.
6. change dns entry from your oldmachine to newmachine
7. shutdown your old machine (if it doesn't host other services or your database)
8. That's it.

Possible enhancements : use right from the start a pound server behind your apache, that way you can add backends and smoothily migrate by shuting down backends that pound will take into account.