Update Infrastructure UI documentation with metric definitions

docs/en/infraops/installation.asciidoc

@@ -50,7 +50,7 @@ image::add-data.png[]
 * If your data source isn't in the list, or you want to install {beats} the old
 fashioned way:
 
-** Follow the 
+** Follow the
 {metricbeat-ref}/metricbeat-getting-started.html[{metricbeat} getting started]
 and enable modules for the metrics you want to collect.
 
@@ -64,10 +64,11 @@ learn how to configure inputs.
 For either approach, you need to enable modules in {filebeat} and {metricbeat}
 to populate the {infra-ui} UI with data.
 
+
 [float]
 ==== Which modules and configuration options do I enable?
 
-To populate the *Hosts* view and add logs, enable: 
+To populate the *Hosts* view and add logs, enable:
 
 * {metricbeat-ref}/metricbeat-module-system.html[{metricbeat} `system` module] (enabled by default)
 * {filebeat-ref}/filebeat-module-system.html[{filebeat} `system` module]
@@ -91,6 +92,58 @@ module]
 * {filebeat-ref}/filebeat-input-docker.html[{filebeat} `docker` input]
 * {filebeat-ref}/add-kubernetes-metadata.html[{filebeat} `add_kubernetes_metadata` processor]
 
+[float]
+==== Which fields are used for the metrics on the Infrastructue home page?
+
+The metrics listed below are provided by the Beats Shippers. Each system type requires their corresponding identity field to be in the same event document:
+
+* Hosts require `host.name`
+* Docker containers require `container.id`
+* Kibernetes pods require `kibernetes.pod.uid`
+
+
+[float]
+===== Host Metrics
+
+*CPU Usage*:: Average of `system.cpu.user.pct` added to the average of `system.cpu.system.pct` divided by `system.cpu.cores`
+
+*Memory Usage*:: Average of `system.memory.actual.used.pct`
+
+*Load*:: Average of `system.load.5`
+
+*Inbound Traffic*:: Derivative of the max of `system.netowrk.in.bytes` scaled to a 1 second rate
+
+*Outbound Traffic*:: Derivative of the max of `system.netowrk.out.bytes` scaled to a 1 second rate
+
+*Log Rate*:: Derivative of the cumulative sum of the document count scaled to a 1 second rate.
+This metric relies on the same indices as the logs.
+
+
+[float]
+===== Docker Container Metrics
+
+*CPU Usage*:: Average of `docker.cpu.total.pct`
+
+*Memory Usage*:: Average of `docker.memory.usage.pct`
+
+*Inbound Traffic*:: Derivative of the max of `docker.network.in.bytes` scaled to a 1 second rate
+
+*Outbound Traffic*:: Derivative of the max of `docker.network.out.bytes` scaled to a 1 second rate
+
+
+[float]
+===== Kubernetes Pod Metrics
+
+*CPU Usage*:: Average of `kubernetes.pod.cpu.usage.node.pct`
+
+*Memory Usage*:: Average of `kubernetes.pod.memory.usage.pct`
+
+*Inbound Traffic*:: Derivative of the max of `kubernetes.pod.network.rx.bytes` scaled to a 1 second rate
+
+*Outbound Traffic*:: Derivative of the max of `kubernetes.pod.network.tx.bytes` scaled to a 1 second rate
+
+
+
 [float]
 ==== More about container monitoring