Comment 0 for bug 1398817

enable_new_services should be False in nova.conf when you scale the env (add more computes to already deployed environment).
See details how it works at: https://github.com/openstack/nova/blob/master/nova/db/sqlalchemy/api.py#L507-L508

The story is the following:
when we deploy new cluster, we want all services to be started, and we want operational environment right after it is deployed. Then, before running production workloads, we test it with HealthCheck feature of Fuel, create test tenant, and run some test workloads first. Then we start running production workloads.

After some time, user needs to scale up: add more compute hosts. If you simply add new computes with Fuel and deploy, they will be automatically registered in Nova DB. If user wants to start a new VM at that time, it will VERY likely go to the new host, as the less loaded one. Needless to say, that the new host might not be ready to accept production load. Before moving any production load on it, administrator of the cloud has to ensure that the new compute is ready for it. It is another story how to do it.

So, a simple step for now would be disable new computes by default, and update Operations Guide: deploy new compute, check that it is ready for production, and manually enable compute via nova-manage command on controller host.