settings: do not query ES for settings in non-green status

If the ui settings status is not green, that means there is at least one
dependency (so elasticsearch at the moment) that is not met in order for
it to function correctly, so we shouldn't attempt to determine user
settings at all.

This ensures that when something like the version check fails in the
elasticsearch plugin, Kibana correctly behaves by not attempting
requests to elasticsearch, which prevents 500 errors and allows users to
see the error status on the status page.

We also now periodically check for compatible elasticsearch versions so
that Kibana can automatically recover if the elasticsearch node is
upgraded to the appropriate version.

src/core_plugins/elasticsearch/lib/health_check.js

@@ -81,13 +81,20 @@ module.exports = function (plugin, server) {
     });
   }
 
+  function waitForEsVersion() {
+    return checkEsVersion(server, kibanaVersion.get()).catch(err => {
+      plugin.status.red(err);
+      return Promise.delay(REQUEST_DELAY).then(waitForEsVersion);
+    });
+  }
+
   function setGreenStatus() {
     return plugin.status.green('Kibana index ready');
   }
 
   function check() {
     return waitForPong()
-    .then(() => checkEsVersion(server, kibanaVersion.get()))
+    .then(waitForEsVersion)
     .then(waitForShards)
     .then(setGreenStatus)
     .then(_.partial(migrateConfig, server))

src/ui/settings/__tests__/index.js

@@ -158,6 +158,14 @@ describe('ui settings', function () {
       })).to.equal(true);
     });
 
+    it('returns an empty object when status is not green', async function () {
+      const { uiSettings, req } = instantiate({
+        settingsStatusOverrides: { state: 'yellow' }
+      });
+
+      expect(await uiSettings.getUserProvided(req)).to.eql({});
+    });
+
     it('returns an empty object on 404 responses', async function () {
       const { uiSettings, req } = instantiate({
         async callWithRequest() {
@@ -361,7 +369,7 @@ function expectElasticsearchUpdateQuery(server, req, configGet, doc) {
   });
 }
 
-function instantiate({ getResult, callWithRequest } = {}) {
+function instantiate({ getResult, callWithRequest, settingsStatusOverrides } = {}) {
   const esStatus = {
     state: 'green',
     on: sinon.spy()
@@ -370,7 +378,8 @@ function instantiate({ getResult, callWithRequest } = {}) {
     state: 'green',
     red: sinon.spy(),
     yellow: sinon.spy(),
-    green: sinon.spy()
+    green: sinon.spy(),
+    ...settingsStatusOverrides
   };
   const kbnServer = {
     status: {

src/ui/settings/index.js

@@ -68,6 +68,13 @@ export default function setupSettings(kbnServer, server, config) {
     assertRequest(req);
     const { callWithRequest, errors } = server.plugins.elasticsearch;
 
+    // If the ui settings status isn't green, we shouldn't be attempting to get
+    // user settings, since we can't be sure that all the necessary conditions
+    // (e.g. elasticsearch being available) are met.
+    if (status.state !== 'green') {
+      return hydrateUserSettings({});
+    }
+
     const params = getClientSettings(config);
     const allowedErrors = [errors[404], errors[403], errors.NoConnections];
     if (ignore401Errors) allowedErrors.push(errors[401]);