vtlim commented on code in PR #13224:
URL: https://github.com/apache/druid/pull/13224#discussion_r995231030


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docs/development/extensions-contrib/prometheus.md:
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@@ -31,6 +31,8 @@ This extension exposes [Druid 
metrics](https://druid.apache.org/docs/latest/oper
 
 Emitter is enabled by setting `druid.emitter=prometheus` 
[configs](https://druid.apache.org/docs/latest/configuration/index.html#emitting-metrics)
 or include `prometheus` in the composing emitter list. 
 
+Note that if you're colocating druid processes on the same host(such as 
broker/router, historical/middlemanager, coordinator/overlord), then the 
druid.emitter.prometheus.port would need to be separately specified in each of 
the runtime properties configuration for each host and be different between 
collocated processes. Additionally peons should emit metrics via push gateway. 

Review Comment:
   A few comments:
   * **Can we break up the first sentence for better readability. Something 
like:** In certain instances, Druid processes may be colocated on the same 
host. For example, the Broker and Router may share the same server. Other 
colocated processes include the Historical and MiddleManager or the Coordinator 
and Overlord.
   * **Code format for properties:** `druid.emitter.prometheus.port`
   * **Prefer active voice:** Specify `druid.emitter.prometheus.port` 
separately ...
   * **Is there a better transition between the colocation and peon tasks? 
Should these be in separate paragraph, or do they cover the same concept 
related to colocated processes?** (Answered in Slack: peons are typically 
collocated with middle managers and most likely historicals as well, but 
because they're using push gateway they would not start an exporter. peons 
instead of starting an http server for the metrics to be scraped , should be 
pushing metrics out)
   
   Most of the above are in the following suggestion. 
   ```suggestion
   In certain instances, Druid processes may be colocated on the same host. For 
example, the Broker and Router may share the same server. Other colocated 
processes include the Historical and MiddleManager or the Coordinator and 
Overlord. When you have colocated processes, specify 
`druid.emitter.prometheus.port` separately for each process on each host. For 
example, even if the Broker and Router share the same host, the Broker runtime 
properties and the Router runtime properties each need to list 
`druid.emitter.prometheus.port`, and the port value for both must be different. 
While peon tasks are typically colocated with MiddleManagers and often 
Historicals, peons should use `pushgateway` for 
`druid.emitter.prometheus.strategy` and should not start an HTTP server to push 
metrics.
   ```



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