abhishekrb19 commented on code in PR #18103:
URL: https://github.com/apache/druid/pull/18103#discussion_r2155346944


##########
docs/configuration/index.md:
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@@ -2031,6 +1893,155 @@ See [cache configuration](#cache-configuration) for how 
to configure cache setti
 |`druid.broker.segment.watchRealtimeTasks`|Boolean|The Broker watches segment 
announcements from processes that serve segments to build a cache to relate 
each process to the segments it serves. When `watchRealtimeTasks` is true, the 
Broker watches for segment announcements from both Historicals and realtime 
processes. To configure a broker to exclude segments served by realtime 
processes, set `watchRealtimeTasks` to false. |true|
 |`druid.broker.segment.awaitInitializationOnStart`|Boolean|Whether the Broker 
will wait for its view of segments to fully initialize before starting up. If 
set to 'true', the Broker's HTTP server will not start up, and the Broker will 
not announce itself as available, until the server view is initialized. See 
also `druid.sql.planner.awaitInitializationOnStart`, a related setting.|true|
 
+## Metrics monitors
+
+You can configure Druid services to emit [metrics](../operations/metrics.md) 
regularly from a number of [monitors](#metrics-monitors-for-each-service) via 
[emitters](#metrics-emitters). The following table lists general configurations 
for metrics:
+
+|Property|Description|Default|
+|--------|-----------|-------|
+|`druid.monitoring.emissionPeriod`| Frequency that Druid emits metrics.|`PT1M`|
+|[`druid.monitoring.monitors`](#metrics-monitors-for-each-service)|Sets list 
of Druid monitors used by a service.|none (no monitors)|
+|[`druid.emitter`](#metrics-emitters)|Setting this value initializes one of 
the emitter modules.|`noop` (metric emission disabled by default)|
+
+### Metrics monitors for each service
+
+:::caution
+
+Because each monitor is meant for a specific service or services, make sure 
you configure them for the correct service unless it is meant for any service. 
For example, if a monitor is meant for the Historical service, configure it in 
`historical/runtime.properties` rather than `_common/common.runtime.properties`.

Review Comment:
   Nice, thanks for adding this! Could we explicitly call out that any monitors 
added in `common/runtime.properties` will be overridden by service-specific 
monitor configurations?
   
   Given this behavior, I’m wondering if we should even recommend adding 
monitors to `common/runtime.properties` at all. Since monitors aren’t additive 
and it’s very likely that users have service-specific monitors defined per 
cluster, this could lead to monitors not being added. Even for monitors marked 
as "Any" in the table below, IMO users would still need to add them to each 
relevant service runtime properties individually for them rather than in 
`common/runtime.properties`.
   
   @kfaraz have you seen any clusters where monitors were actually added via 
`common/runtime.properties`?



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