The master-is-stable indicator will retrieve useful information
regarding the discovery. This will be useful even if the local
cluster state is not recovered.

We currently do not evaluate the instance-has-master indicator
if the cluster state is not recovered, but we should remove this
constraint once master-is-stable is merged
server/src/main/java/org/elasticsearch/health/HealthService.java
/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */
package org.elasticsearch.health;
import org.elasticsearch.ResourceNotFoundException;
import org.elasticsearch.cluster.service.ClusterService;
import org.elasticsearch.core.Nullable;
import org.elasticsearch.gateway.GatewayService;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import static java.util.function.Predicate.isEqual;
import static java.util.stream.Collectors.collectingAndThen;
import static java.util.stream.Collectors.groupingBy;
import static java.util.stream.Collectors.toList;
import static java.util.stream.Collectors.toMap;
/**
 * This service collects health indicators from all modules and plugins of elasticsearch
 */
public class HealthService {