Assistance needed in creating a watcher alert for specific hostnames if the CPU/memory goes above certain threshold

The existing threshold alert does what I need but its taking into account all the agents that are reporting to kibana using metricbeat. I only want the watcher for specific server say serverA reports a CPU level of 90% for last 5 mins then send an email. How can I do that?

Assuming you are talking about the new KIbana Alerting Framework you can add a filter...
You can filter by host.name or any other term / tag (example data_center : "DC1") and then create an alert per host using the Create alert per option below

Thank you. Yes this is what I was looking for.