通过删除的成员连接到副本集成员

Question

我有一个简单的副本集，有3个成员

rs.status()的输出

{
    ...,
    "members" : [
        {
            "_id": 1,
            "name": "localhost:27021",
            "stateStr": "PRIMARY",
        },
        {
            "_id": 2,
            "name": "localhost:27022",
            "stateStr": "SECONDARY",
        },
        {
            "_id": 3,
            "name": "localhost:27023",
            "stateStr": "SECONDARY",
        }
    ]
}

我移走了一个成员

rs.remove("localhost:27023")

现在rs.status()

{
    ...,
    "members" : [
        {
            "_id": 1,
            "name": "localhost:27021",
            "stateStr": "PRIMARY",
        },
        {
            "_id": 2,
            "name": "localhost:27022",
            "stateStr": "SECONDARY",
        },
    ]
}

现在，我使用了带有已删除实例的mongodb连接URL。它成功地连接到复制集成员！！

var url = 'mongodb://localhost:27023/myproject?replicaSet=rs0';
MongoClient.connect(url, function(err, db) {
  console.log("Connected correctly to server");
  db.close();
});

我可以看到连接是用副本集成员(localhost:27022和localhost:27023)建立的。

2019-04-17T18:59:04.727+0900 I NETWORK  [thread1] connection accepted from 127.0.0.1:53284 #6 (3 connections now open)
2019-04-17T18:59:04.727+0900 I NETWORK  [conn6] received client metadata from 127.0.0.1:53284 conn6: { driver: { name: "nodejs", version: "3.2.3" }, os: { type: "Linux", name: "linux", architecture: "x64", version: "4.15.0-47-generic" }, platform: "Node.js v10.15.0, LE, mongodb-core: 3.2.3" }
2019-04-17T18:59:04.736+0900 I -        [conn6] end connection 127.0.0.1:53284 (3 connections now open)
2019-04-17T18:59:35.334+0900 I ASIO     [NetworkInterfaceASIO-RS-0] Ending idle connection to host localhost:27021 because the pool meets constraints; 1 connections to that host remain open

有人能解释一下吗？通过删除的成员连接到副本集成员。在任何文档中找不到任何解释。

Answer 1

这是司机的行为。默认情况下，客户端连接到副本集将尝试连接到主节点。在这种情况下，连接到mongodb://localhost:27023/myproject?replicaSet=rs0将首先连接到localhost:27023，并使用命令{isMaster: 1}检查所连接的节点是否是主/主节点。从结果中，它检测到localhost:27023不是主/主节点，但它也有其他可用的节点信息。接下来的步骤是连接到其他节点，直到找到主节点为止。

你应该关闭localhost:27023，它甚至连不上。