@Love_Cat
Can you share the steps before you invoke Ambari?
Did you install the agent and edit the below portion of the ambari-agent.ini?
[server]
hostname=<Current_Ambari_host>
url_port=8440
secured_url_port=8441
connect_retry_delay=10
max_reconnect_retry_delay=30
And restarted the agent thereafter this should show in the ambari UI in the Add host Wizard assuming you generated and copied the SSH Private key with the correct permissions
Please share your steps so we could help you resolve