@vumanhtai , I don't know your network setup nor your application architecture so it is difficult to comment on why you have the HF setup to only check one node and why it can't check more than one node at a time.
It sounds like you have some technical restrictions that would prevent you from using a single HF to check multiple nodes as well as the VIP. I would recommend working with your network and infrastructure team and explain what you are trying to do and if they have recommendations.
You can install Splunk Enterprise as a HF on your individual server nodes and then install Website_Monitoring on each node and have the nodes check themselves via the localhost or server name. I still would not recommend this as this is a lot of additional overhead and complexity to manage.
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