You can install agents on active/passive cluster and use the following guide to relocate your targets like databases.
Configuring Targets for Failover in Active/Passive Environments:
You can refer to below metalink doc for detailed steps on how to install 12c agent on virtual host
How to Install 12c Agent on Virtual Host (Doc ID 1469995.1)
Below is the Doc summary
1. From the 12c Console you can install Agent on Virtual Host using the 'Add Host Targets' Wizard. We must add the virtual host explicitly as a destination host.
Refer to the documentation at Oracle® Enterprise Manager Cloud Control Basic Installation Guide 12c Release 1 (184.108.40.206), Chapter 8 - Installing Oracle Management Agent
Note 1360183.1: How to install Enterprise Manager Cloud Control 12c Agent on Linux
It is similar to installation of normal agent. Instead of Physical Hostname, we provide virtual hostname as a target server.
2.You can install the Agent in Silent Method using Response file as per documentation
Oracle® Enterprise Manager Cloud Control Advanced Installation and Configuration Guide 12c Release 1 (220.127.116.11), Chapter 5 - Installing Oracle Management Agent in Silent Mode
In the response file, provide ORACLE_HOSTNAME value to virtual hostname.
And also run "agentDeploy.sh" by providing the parameter ORACLE_HOSTNAME=VirtualHostName
<software_extract_location>/agentDeploy.sh AGENT_BASE_DIR=<absolute_path_to_agentbasedir> RESPONSE_FILE=<absolute_path_to_responsefile> ORACLE_HOSTNAME=VirtualHostName
If you would like to use the same Agent port for both Physical agent as well as for the Agent on virtual Host, Please do the following action plan on both the agents before starting the agent on virtual host.
1.Have a backup of emd.properties file from <AGENT_INST_HOME>/sysman/config/
2.Set the value of "AgentListenOnAllNICS" to FALSE in emd.properties.