<processor url> is the URL where of the build messages processor will operate. This URL must be accessible by both the agents and main server. If you do not have an HTTP proxy installed in front of the TeamCity servlet container and you did not change the port in the servlet container during the installation, then by default this URL will be:
http://<your host name>:8111/
Both main TeamCity server and build messages processor can be started / stopped using regular TeamCity scripts:
teamcity-server.sh or Windows services.
If both - the main server and build messages processor are up and running, you should see the "Administration | Nodes configuration" page in the Administration area on the main TeamCity server:
And vice versa, if you decide to disable the messages processor, only the newly started builds will be switched to the main server, the builds that were already running on the messages processor will continue running there.
At any point of time On this page you can also see how many builds are currently assigned to each node. If everything is configured correctly (the node is accessible by agents) and there are no problems with processing builds on the build messages processor is enabled, eventually all of the running builds should be switched to the messages processor once you enable it.this node.
Restarting Servers while Builds are Running