If your site is volatile enough that the routing needs to change that often then there is something wrong either with your information architecture or your development process.
1. take s01 out of pool.
2. migrate config on s01 to new config.
3. put s01 back in pool.
4. take s02 out of pool
5. migrate config on s02 to new config.
6. put s02 back in pool.
Ansible can handle this quite happily. Scales up to any number of boxes. For an (n-1)/n capacity reduction during deployment.
I've got a 450k apache config somewhere that takes <1 second to reload so I don't think that's a major issue.
Also if you have THAT much config, something is wrong with your information architecture (see my other points).
It really sounds like a dynamic front-end that is aware of the routes would be a much better idea, far less that can go wrong.
The biggest point of failure is always humans and you're basically handing them a gun there.
