Deprecate kibana.defaultAppId setting

docs/setup/docker.asciidoc

@@ -93,7 +93,7 @@ Some example translations are shown here:
 [horizontal]
 **Environment Variable**:: **Kibana Setting**
 `SERVER_NAME`:: `server.name`
-`KIBANA_DEFAULTAPPID`:: `kibana.defaultAppId`
+`SERVER_BASEPATH`:: `server.basePath`
 `MONITORING_ENABLED`:: `monitoring.enabled`
 
 In general, any setting listed in <<settings>> can be

docs/setup/settings.asciidoc

@@ -216,7 +216,9 @@ on the {kib} index at startup. {kib} users still need to authenticate with
   | Enables use of interpreter in Visualize. *Default: `true`*
 
 | `kibana.defaultAppId:`
- | The default application to load. *Default: `"home"`*
+ | *deprecated* This setting is deprecated and will get removed in Kibana 8.0.
+Please use the `defaultRoute` advanced setting instead.
+The default application to load. *Default: `"home"`*
 
 | `kibana.index:`
  | {kib} uses an index in {es} to store saved searches, visualizations, and

src/plugins/kibana_legacy/server/index.ts

@@ -17,7 +17,13 @@
  * under the License.
  */
 
-import { CoreSetup, CoreStart, PluginConfigDescriptor } from 'kibana/server';
+import {
+  ConfigDeprecationLogger,
+  CoreSetup,
+  CoreStart,
+  PluginConfigDescriptor,
+} from 'kibana/server';
+import { get } from 'lodash';
 
 import { configSchema, ConfigSchema } from '../config';
 
@@ -29,6 +35,18 @@ export const config: PluginConfigDescriptor<ConfigSchema> = {
   deprecations: ({ renameFromRoot }) => [
     // TODO: Remove deprecation once defaultAppId is deleted
     renameFromRoot('kibana.defaultAppId', 'kibana_legacy.defaultAppId', true),
+    (completeConfig: Record<string, any>, rootPath: string, log: ConfigDeprecationLogger) => {
+      if (
+        get(completeConfig, 'kibana.defaultAppId') === undefined &&
+        get(completeConfig, 'kibana_legacy.defaultAppId') === undefined
+      ) {
+        return completeConfig;
+      }
+      log(
+        `kibana.defaultAppId is deprecated and will be removed in 8.0. Please use the \`defaultRoute\` advanced setting instead`
+      );
+      return completeConfig;
+    },
   ],
 };