使用health api可以查看es集群的健康度。 health api的用法如下:
curl 'http://localhost:9200/_cluster/health'health api的返回值中有一个核心的字段status， status 有3种取值: green, yellow, red。分别代表集群的3种状态: 主分片和副本都已经分配，主分片已经分配副本分片没有，主分片和副本都都没有分配。
也就是说， health api关注的核心在于数据的高可用。
看health api的实现:
请求会路由到master节点，然后读取clusterState中的routing_table.
基于routing_table, 判断索引的各个分片状态
public ClusterShardHealth(int shardId, final IndexShardRoutingTable shardRoutingTable) { this.shardId = shardId; for (ShardRouting shardRouting : shardRoutingTable) { if (shardRouting.active()) { activeShards++; if (shardRouting.relocating()) { // the shard is relocating, the one it is relocating to will be in initializing state, so we don't count it relocatingShards++; } if (shardRouting.primary()) { primaryActive = true; } } else if (shardRouting.initializing()) { initializingShards++; } else if (shardRouting.unassigned()) { unassignedShards++; } } if (primaryActive) { if (activeShards == shardRoutingTable.size()) { status = ClusterHealthStatus.GREEN; } else { status = ClusterHealthStatus.YELLOW; } } else { status = ClusterHealthStatus.RED; } }基于分片，决定索引的状态
public ClusterIndexHealth(IndexMetaData indexMetaData, IndexRoutingTable indexRoutingTable) { this.index = indexMetaData.getIndex(); this.numberOfShards = indexMetaData.getNumberOfShards(); this.numberOfReplicas = indexMetaData.getNumberOfReplicas(); this.validationFailures = indexRoutingTable.validate(indexMetaData); for (IndexShardRoutingTable shardRoutingTable : indexRoutingTable) { int shardId = shardRoutingTable.shardId().id(); shards.put(shardId, new ClusterShardHealth(shardId, shardRoutingTable)); } // update the index status status = ClusterHealthStatus.GREEN; for (ClusterShardHealth shardHealth : shards.values()) { if (shardHealth.isPrimaryActive()) { activePrimaryShards++; } activeShards += shardHealth.getActiveShards(); relocatingShards += shardHealth.getRelocatingShards(); initializingShards += shardHealth.getInitializingShards(); unassignedShards += shardHealth.getUnassignedShards(); if (shardHealth.getStatus() == ClusterHealthStatus.RED) { status = ClusterHealthStatus.RED; } else if (shardHealth.getStatus() == ClusterHealthStatus.YELLOW && status != ClusterHealthStatus.RED) { // do not override an existing red status = ClusterHealthStatus.YELLOW; } } if (!validationFailures.isEmpty()) { status = ClusterHealthStatus.RED; } else if (shards.isEmpty()) { // might be since none has been created yet (two phase index creation) status = ClusterHealthStatus.RED; } }基于索引，决定集群的状态。
public ClusterStateHealth(ClusterState clusterState, String[] concreteIndices) { RoutingTableValidation validation = clusterState.routingTable().validate(clusterState.metaData()); validationFailures = validation.failures(); numberOfNodes = clusterState.nodes().size(); numberOfDataNodes = clusterState.nodes().dataNodes().size(); for (String index : concreteIndices) { IndexRoutingTable indexRoutingTable = clusterState.routingTable().index(index); IndexMetaData indexMetaData = clusterState.metaData().index(index); if (indexRoutingTable == null) { continue; } ClusterIndexHealth indexHealth = new ClusterIndexHealth(indexMetaData, indexRoutingTable); indices.put(indexHealth.getIndex(), indexHealth); } status = ClusterHealthStatus.GREEN; for (ClusterIndexHealth indexHealth : indices.values()) { activePrimaryShards += indexHealth.getActivePrimaryShards(); activeShards += indexHealth.getActiveShards(); relocatingShards += indexHealth.getRelocatingShards(); initializingShards += indexHealth.getInitializingShards(); unassignedShards += indexHealth.getUnassignedShards(); if (indexHealth.getStatus() == ClusterHealthStatus.RED) { status = ClusterHealthStatus.RED; } else if (indexHealth.getStatus() == ClusterHealthStatus.YELLOW && status != ClusterHealthStatus.RED) { status = ClusterHealthStatus.YELLOW; } } if (!validationFailures.isEmpty()) { status = ClusterHealthStatus.RED; } else if (clusterState.blocks().hasGlobalBlock(RestStatus.SERVICE_UNAVAILABLE)) { status = ClusterHealthStatus.RED; } // shortcut on green if (status.equals(ClusterHealthStatus.GREEN)) { this.activeShardsPercent = 100; } else { List<ShardRouting> shardRoutings = clusterState.getRoutingTable().allShards(); int activeShardCount = 0; int totalShardCount = 0; for (ShardRouting shardRouting : shardRoutings) { if (shardRouting.active()) activeShardCount++; totalShardCount++; } this.activeShardsPercent = (((double) activeShardCount) / totalShardCount) * 100; } }理解health api, 需要理解clusterState。 好在这些都是只读的信息，不难理解。
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