Generalize TCP retxn docs to cover remote clusters (#74732)

Today the docs on setting `tcp_retries2` only talk about intra-cluster
connections, but in fact this setting is equally important to the
resilience of remote cluster connections too. This commit rewords these
docs to cover both cases.

Relates #34405

Author: DaveCTurner

docs/reference/setup/sysconfig/tcpretries.asciidoc

@@ -1,32 +1,38 @@
 [[system-config-tcpretries]]
 === TCP retransmission timeout
 
-Each pair of nodes in a cluster communicates via a number of TCP connections
-which <<long-lived-connections,remain open>> until one of the nodes shuts down
-or communication between the nodes is disrupted by a failure in the underlying
+Each pair of {es} nodes communicates via a number of TCP connections which
+<<long-lived-connections,remain open>> until one of the nodes shuts down or
+communication between the nodes is disrupted by a failure in the underlying
 infrastructure.
 
-TCP provides reliable communication over occasionally-unreliable networks by
+TCP provides reliable communication over occasionally unreliable networks by
 hiding temporary network disruptions from the communicating applications. Your
 operating system will retransmit any lost messages a number of times before
-informing the sender of any problem. Most Linux distributions default to
-retransmitting any lost packets 15 times. Retransmissions back off
-exponentially, so these 15 retransmissions take over 900 seconds to complete.
-This means it takes Linux many minutes to detect a network partition or a
-failed node with this method. Windows defaults to just 5 retransmissions which
-corresponds with a timeout of around 6 seconds.
+informing the sender of any problem. {es} must wait while the retransmissions
+are happening and can only react once the operating system decides to give up.
+Users must therefore also wait for a sequence of retransmissions to complete.
+
+Most Linux distributions default to retransmitting any lost packets 15 times.
+Retransmissions back off exponentially, so these 15 retransmissions take over
+900 seconds to complete. This means it takes Linux many minutes to detect a
+network partition or a failed node with this method. Windows defaults to just 5
+retransmissions which corresponds with a timeout of around 6 seconds.
 
 The Linux default allows for communication over networks that may experience
-very long periods of packet loss, but this default is excessive for production
-networks within a single data centre as is the case for most {es} clusters.
-Highly-available clusters must be able to detect node failures quickly so that
-they can react promptly by reallocating lost shards, rerouting searches and
-perhaps electing a new master node. Linux users should therefore reduce the
-maximum number of TCP retransmissions.
+very long periods of packet loss, but this default is excessive and even harmful
+on the high quality networks used by most {es} installations. When a cluster
+detects a node failure it reacts by reallocating lost shards, rerouting
+searches, and maybe electing a new master node. Highly available clusters must
+be able to detect node failures promptly, which can be achieved by reducing the
+permitted number of retransmissions. Connections to
+<<modules-remote-clusters,remote clusters>> should also prefer to detect
+failures much more quickly than the Linux default allows. Linux users should
+therefore reduce the maximum number of TCP retransmissions.
 
-You can decrease the maximum number of TCP retransmissions to `5` by running
-the following command as `root`. Five retransmissions corresponds with a
-timeout of around six seconds.
+You can decrease the maximum number of TCP retransmissions to `5` by running the
+following command as `root`. Five retransmissions corresponds with a timeout of
+around six seconds.
 
 [source,sh]
 -------------------------------------
@@ -38,8 +44,8 @@ To set this value permanently, update the `net.ipv4.tcp_retries2` setting in
 `sysctl net.ipv4.tcp_retries2`.
 
 IMPORTANT: This setting applies to all TCP connections and will affect the
-reliability of communication with systems outside your cluster too. If your
-cluster communicates with external systems over an unreliable network then you
+reliability of communication with systems other than {es} clusters too. If your
+clusters communicate with external systems over a low quality network then you
 may need to select a higher value for `net.ipv4.tcp_retries2`. For this reason,
 {es} does not adjust this setting automatically.
 
@@ -54,6 +60,6 @@ related to these application-level health checks.
 You must also ensure your network infrastructure does not interfere with the
 long-lived connections between nodes, <<long-lived-connections,even if those
 connections appear to be idle>>. Devices which drop connections when they reach
-a certain age are a common source of problems to Elasticsearch clusters, and
-must not be used.
+a certain age are a common source of problems to {es} clusters, and must not be
+used.