More docs re. removing cluster.initial_master_nodes (elastic#85948)

Ensures that on every page of the docs that mentions
`cluster.initial_master_nodes` also mentions that this setting must be
removed after bootstrapping completes.

Author: DaveCTurner

docs/reference/modules/discovery.asciidoc

@@ -32,9 +32,7 @@ formation:
     themselves. As this auto-bootstrapping is
     <<modules-discovery-quorums,inherently unsafe>>, running a node in
     <<dev-vs-prod-mode,production mode>> requires bootstrapping to be
-    explicitly configured via the
-    <<modules-discovery-bootstrap-cluster,`cluster.initial_master_nodes`
-    setting>>.
+    <<modules-discovery-bootstrap-cluster,explicitly configured>>.
 
 <<modules-discovery-adding-removing-nodes,Adding and removing master-eligible nodes>>::
 

docs/reference/modules/discovery/bootstrapping.asciidoc

@@ -31,8 +31,9 @@ node:
 
 When you start a master-eligible node, you can provide this setting on the
 command line or in the `elasticsearch.yml` file. After the cluster has formed,
-this setting is no longer required. It should not be set for master-ineligible
-nodes, master-eligible nodes joining an existing cluster, or cluster restarts.
+remove this setting from each node's configuration. It should not be set for
+master-ineligible nodes, master-eligible nodes joining an existing cluster, or
+when restarting one or more nodes.
 
 It is technically sufficient to set `cluster.initial_master_nodes` on a single
 master-eligible node in the cluster, and only to mention that single node in the

docs/reference/modules/discovery/discovery-settings.asciidoc

@@ -50,9 +50,11 @@ this setting, see <<single-node-discovery>>.
 
 `cluster.initial_master_nodes`::
 (<<static-cluster-setting,Static>>)
-Sets the initial set of master-eligible nodes in a brand-new cluster. By default
-this list is empty, meaning that this node expects to join a cluster that has
-already been bootstrapped. See <<initial_master_nodes>>.
+Sets the initial set of master-eligible nodes in a brand-new cluster. By
+default this list is empty, meaning that this node expects to join a cluster
+that has already been bootstrapped. Remove this setting once the cluster has
+formed. Do not use this setting when restarting nodes or when adding new nodes
+to an existing cluster. See <<initial_master_nodes>>.
 
 [discrete]
 ==== Expert settings

docs/reference/setup/bootstrap-checks.asciidoc

@@ -254,3 +254,11 @@ properties:
 - `discovery.seed_hosts`
 - `discovery.seed_providers`
 - `cluster.initial_master_nodes`
+
+Note that you should remove `cluster.initial_master_nodes` from the
+configuration after the cluster has started for the first time. Do not use this
+setting when restarting nodes or when adding new nodes to an existing cluster.
+Instead, configure `discovery.seed_hosts` or `discovery.seed_providers`. If you
+do not need any discovery configuration, for instance if running a single-node
+cluster, set `discovery.seed_hosts: []` to disable discovery and satisfy this
+bootstrap check.

docs/reference/setup/important-settings/discovery-settings.asciidoc

@@ -59,9 +59,10 @@ mode, you must explicitly list the master-eligible nodes whose votes should be
 counted in the very first election. You set this list using the
 `cluster.initial_master_nodes` setting.
 
-IMPORTANT: After the cluster forms successfully for the first time, remove the `cluster.initial_master_nodes` setting from each nodes'
-configuration. Do not use this setting when
-restarting a cluster or adding a new node to an existing cluster.
+IMPORTANT: After the cluster forms successfully for the first time, remove the
+`cluster.initial_master_nodes` setting from each node's configuration. Do not
+use this setting when restarting a cluster or adding a new node to an existing
+cluster.
 
 [source,yaml]
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