Add publicBaseUrl to Elasticsearch config (#191837)

## Summary

This adds a publicBaseUrl to the Elasticsearch plugin config so users
can set a publicly accessible URL for Elasticsearch.

---------

Co-authored-by: Rudolf Meijering <skaapgif@gmail.com>

docs/setup/settings.asciidoc

@@ -14,7 +14,7 @@ KBN_PATH_CONF=/home/kibana/config ./bin/kibana
 --
 
 The default host and port settings configure {kib} to run on `localhost:5601`. To change this behavior and allow remote users to connect, you'll need to update your `kibana.yml` file. You can also enable SSL and set a
-variety of other options. 
+variety of other options.
 
 Environment variables can be injected into configuration using `${MY_ENV_VAR}` syntax. By default, configuration validation
 will fail if an environment variable used in the config file is not present when Kibana starts. This behavior can be changed by using a default value
@@ -93,7 +93,7 @@ The maximum number of sockets that can be used for communications with {es}.
 *Default: `Infinity`*
 
 [[elasticsearch-maxResponseSize]] `elasticsearch.maxResponseSize`::
-Either `false` or a `byteSize` value. When set, responses from {es} with a size higher than the defined limit will be rejected. 
+Either `false` or a `byteSize` value. When set, responses from {es} with a size higher than the defined limit will be rejected.
 This is intended to be used as a circuit-breaker mechanism to avoid memory errors in case of unexpectedly high responses coming from {es}.
 *Default: `false`*
 
@@ -117,6 +117,9 @@ listed here must be on the same cluster. *Default: `[ "http://localhost:9200" ]`
 To enable SSL/TLS for outbound connections to {es}, use the `https` protocol
 in this setting.
 
+[[elasticsearch-publicBaseUrl]] `elasticsearch.publicBaseUrl:`::
+The URL through which Elasticsearch is publicly accessible, if any. This will be shown to users in Kibana when they need connection details for your Elasticsearch cluster.
+
 [[elasticsearch-pingTimeout]] `elasticsearch.pingTimeout`::
 Time in milliseconds to wait for {es} to respond to pings.
 *Default: the value of the <<elasticsearch-requestTimeout, `elasticsearch.requestTimeout`>> setting*
@@ -470,7 +473,7 @@ identifies this {kib} instance. *Default: `"your-hostname"`*
 setting specifies the port to use. *Default: `5601`*
 
 `server.protocol`::
-experimental[] The http protocol to use, either `http1` or `http2`. Set to `http2` to enable `HTTP/2` support for the {kib} server. 
+experimental[] The http protocol to use, either `http1` or `http2`. Set to `http2` to enable `HTTP/2` support for the {kib} server.
 *Default: `http1`*
 +
 NOTE: By default, enabling `http2` requires a valid `h2c` configuration, meaning that TLS must be enabled via <<server-ssl-enabled, `server.ssl.enabled`>>

packages/core/elasticsearch/core-elasticsearch-server-internal/src/elasticsearch_config.ts

@@ -190,6 +190,7 @@ export const configSchema = schema.object({
     { defaultValue: [] }
   ),
   dnsCacheTtl: schema.duration({ defaultValue: 0, min: 0 }),
+  publicBaseUrl: schema.maybe(hostURISchema),
 });
 
 const deprecations: ConfigDeprecationProvider = () => [

packages/core/elasticsearch/core-elasticsearch-server/src/contracts.ts

@@ -90,6 +90,12 @@ export interface ElasticsearchServiceSetup {
      */
     readonly config$: Observable<IElasticsearchConfig>;
   };
+
+  /**
+   * The public base URL (if any) that should be used by end users to access the Elasticsearch cluster.
+   */
+
+  readonly publicBaseUrl?: string;
 }
 
 /**

x-pack/plugins/cloud/server/plugin.ts

@@ -202,7 +202,7 @@ export class CloudPlugin implements Plugin<CloudSetup, CloudStart> {
       organizationId,
       instanceSizeMb: readInstanceSizeMb(),
       deploymentId,
-      elasticsearchUrl: decodedId?.elasticsearchUrl,
+      elasticsearchUrl: core.elasticsearch.publicBaseUrl || decodedId?.elasticsearchUrl,
       kibanaUrl: decodedId?.kibanaUrl,
       cloudHost: decodedId?.host,
       cloudDefaultPort: decodedId?.defaultPort,