Docs: Added cluster naming advice to setup and getting started docs

docs/reference/getting-started.asciidoc

@@ -28,7 +28,12 @@ Elasticsearch is a near real time search platform. What this means is there is a
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 === Cluster
 
-A cluster is a collection of one or more nodes (servers) that together holds your entire data and provides federated indexing and search capabilities across all nodes. A cluster is identified by a unique name which by default is "elasticsearch". This name is important because a node can only be part of a cluster if the node is set up to join the cluster by its name. It is good practice to explicitly set the cluster name in production, but it is fine to use the default for testing/development purposes.
+A cluster is a collection of one or more nodes (servers) that together holds your entire data and provides federated indexing and search capabilities across all nodes. A cluster is identified by a unique name which by default is "elasticsearch". This name is important because a node can only be part of a cluster if the node is set up to join the cluster by its name.
+
+Make sure that you don't reuse the same cluster names in different
+environments, otherwise you might end up with nodes joining the wrong cluster.
+For instance you could use `logging-dev`, `logging-stage`, and `logging-prod`
+for the development, staging, and production clusters.
 
 Note that it is valid and perfectly fine to have a cluster with only a single node in it. Furthermore, you may also have multiple independent clusters each with its own unique cluster name.
 

docs/reference/setup/configuration.asciidoc

@@ -135,7 +135,7 @@ curl http://localhost:9200/_nodes/process?pretty
 
 If you see that `mlockall` is `false`, then it means that the the `mlockall`
 request has failed.  The most probable reason, on Linux/Unix systems, is that
-the user running Elasticsearch doesn't have permission to lock memory.  This can 
+the user running Elasticsearch doesn't have permission to lock memory.  This can
 be granted by running `ulimit -l unlimited` as `root` before starting Elasticsearch.
 
 Another possible reason why `mlockall` can fail is that the temporary directory
@@ -199,6 +199,11 @@ cluster:
   name: <NAME OF YOUR CLUSTER>
 --------------------------------------------------
 
+Make sure that you don't reuse the same cluster names in different
+environments, otherwise you might end up with nodes joining the wrong cluster.
+For instance you could use `logging-dev`, `logging-stage`, and `logging-prod`
+for the development, staging, and production clusters.
+
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 [[node-name]]
 ==== Node name
@@ -363,8 +368,8 @@ appender section contains the destinations for the logs. Extensive information
 on how to customize logging and all the supported appenders can be found on
 the http://logging.apache.org/log4j/1.2/manual.html[log4j documentation].
 
-Additional Appenders and other logging classes provided by 
-http://logging.apache.org/log4j/extras/[log4j-extras] are also available, 
+Additional Appenders and other logging classes provided by
+http://logging.apache.org/log4j/extras/[log4j-extras] are also available,
 out of the box.
 
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