anchor.diff:  *Details* +
   The `xpack.security.authc.realms.{type}.{name}.order` setting is now required and must be
   specified for each explicitly configured realm. Each value must be unique.
  +
  +*Impact* +
   The cluster will fail to start if the requirements are not met.
   
   For example, the following configuration is invalid:
  
positive.code: It is now an error to configure any SSL settings for
  `xpack.security.http.ssl` without also configuring
  `xpack.security.http.ssl.enabled`.
  
  For example, the following configuration is invalid:
  [source,yaml]
  
negative.code: `xpack.security.transport.ssl` without also configuring
  `xpack.security.transport.ssl.enabled`.
  
  *Impact* +
  If using other `xpack.security.transport.ssl` settings, you must explicitly
  specify the `xpack.security.transport.ssl.enabled` setting.
  
  If you do not want to enable SSL and are currently using other
  `xpack.security.transport.ssl` settings, do one of the following:
  
  * Explicitly specify `xpack.security.transport.ssl.enabled` as `false`
  * Discontinue use of other `xpack.security.transport.ssl` settings
  
  If you want to enable SSL, follow the instructions in
  {ref}/configuring-tls.html#tls-transport[Encrypting communications between nodes
  in a cluster]. As part of this configuration, explicitly specify
  `xpack.security.transport.ssl.enabled` as `true`.
  
  For example, the following configuration is invalid:
  [source,yaml]
  --------------------------------------------------
  