Add deprecation warning if setting server.host to "0" (#87471)

src/core/server/config/deprecation/core_deprecations.test.ts

@@ -120,6 +120,26 @@ describe('core deprecations', () => {
     });
   });
 
+  describe('server.host', () => {
+    it('logs a warning if server.host is set to "0"', () => {
+      const { messages } = applyCoreDeprecations({
+        server: { host: '0' },
+      });
+      expect(messages).toMatchInlineSnapshot(`
+        Array [
+          "Support for setting server.host to \\"0\\" in kibana.yml is deprecated and will be removed in Kibana version 8.0.0. Instead use \\"0.0.0.0\\" to bind to all interfaces.",
+        ]
+      `);
+    });
+    it('does not log a warning if server.host is not set to "0"', () => {
+      const { migrated, messages } = applyCoreDeprecations({
+        server: { host: '0.0.0.0' },
+      });
+      expect(migrated.server.host).toEqual('0.0.0.0');
+      expect(messages.length).toBe(0);
+    });
+  });
+
   describe('rewriteBasePath', () => {
     it('logs a warning is server.basePath is set and server.rewriteBasePath is not', () => {
       const { messages } = applyCoreDeprecations({

src/core/server/config/deprecation/core_deprecations.ts

@@ -114,6 +114,16 @@ const mapManifestServiceUrlDeprecation: ConfigDeprecation = (settings, fromPath,
   return settings;
 };
 
+const serverHostZeroDeprecation: ConfigDeprecation = (settings, fromPath, log) => {
+  if (get(settings, 'server.host') === '0') {
+    log(
+      'Support for setting server.host to "0" in kibana.yml is deprecated and will be removed in Kibana version 8.0.0. ' +
+        'Instead use "0.0.0.0" to bind to all interfaces.'
+    );
+  }
+  return settings;
+};
+
 export const coreDeprecationProvider: ConfigDeprecationProvider = ({
   unusedFromRoot,
   renameFromRoot,
@@ -159,4 +169,5 @@ export const coreDeprecationProvider: ConfigDeprecationProvider = ({
   rewriteBasePathDeprecation,
   cspRulesDeprecation,
   mapManifestServiceUrlDeprecation,
+  serverHostZeroDeprecation,
 ];