If you are changing the servers URL in your migration, which from your question I am assuming that you are, then you will need to edit each build agent's properties.
In your ~TeamCity\Install\buildAgent\conf
, you will have a buildAgent.properties
file. You need to modify this file to point to your new Teamcity location via the serverURL
value. Then you will want to restart the build agent server, and authorize and enable the build agent from your Teamcity interface.
There is an extremely brief explanation of this here at the bottom of the "Move TeamCity Installation to a New Machine" section.
And to answer your question as to why the agent pool seems empty - it is because the agent is not looking for the server at it's new location.