MongoDB副本集中,如果要指定某些节点不能被选为primary节点,或者primary节点必须在某些节点中选出,该怎么配置呢?可以通过priority修改优先级。
 

场景:

  • 副本集中个别节点配置略低,禁止成为primary节点。
  • 延迟节点或者隐藏节点禁止成为primary节点。
  • 跨机房的副本集,比如A机房作为生产环境,B机房作为灾备环境。
     

查看节点优先级

handong1:PRIMARY> rs.config()
{
    "_id" : "handong1",
    "version" : 18,
    "protocolVersion" : NumberLong(1),
    "writeConcernMajorityJournalDefault" : true,
    "members" : [
        {
            "_id" : 0,
            "host" : "172.16.254.131:27017",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 2,
            "tags" : {

            },
            "slaveDelay" : NumberLong(0),
            "votes" : 1
        },
        {
            "_id" : 1,
            "host" : "mongo2:27017",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 1,
            "tags" : {

            },
            "slaveDelay" : NumberLong(0),
            "votes" : 1
        },
        {
            "_id" : 2,
            "host" : "mongo3:27017",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 1,
            "tags" : {

            },
            "slaveDelay" : NumberLong(0),
            "votes" : 1
        },
        {
            "_id" : 3,
            "host" : "mongo4:27017",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 1,
            "tags" : {

            },
            "slaveDelay" : NumberLong(0),
            "votes" : 1
        }
    ],
    "settings" : {
        "chainingAllowed" : true,
        "heartbeatIntervalMillis" : 2000,
        "heartbeatTimeoutSecs" : 10,
        "electionTimeoutMillis" : 10000,
        "catchUpTimeoutMillis" : -1,
        "catchUpTakeoverDelayMillis" : 30000,
        "getLastErrorModes" : {

        },
        "getLastErrorDefaults" : {
            "w" : 1,
            "wtimeout" : 0
        },
        "replicaSetId" : ObjectId("6051ca21a1f8138a01c3b940")
    }
}

可以看到每个节点priority默认都为1。

为了避免mongo4:27017成为primary节点,修改priority为0。

handong1:PRIMARY> cfg = rs.conf()
{
    "_id" : "handong1",
    "version" : 19,
    "protocolVersion" : NumberLong(1),
    "writeConcernMajorityJournalDefault" : true,
    "members" : [
        {
            "_id" : 0,
            "host" : "172.16.254.131:27017",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 2,
            "tags" : {

            },
            "slaveDelay" : NumberLong(0),
            "votes" : 1
        },
        {
            "_id" : 1,
            "host" : "mongo2:27017",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 1,
            "tags" : {

            },
            "slaveDelay" : NumberLong(0),
            "votes" : 1
        },
        {
            "_id" : 2,
            "host" : "mongo3:27017",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 1,
            "tags" : {

            },
            "slaveDelay" : NumberLong(0),
            "votes" : 1
        },
        {
            "_id" : 3,
            "host" : "mongo4:27017",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 1,
            "tags" : {

            },
            "slaveDelay" : NumberLong(0),
            "votes" : 1
        }
    ],
    "settings" : {
        "chainingAllowed" : true,
        "heartbeatIntervalMillis" : 2000,
        "heartbeatTimeoutSecs" : 10,
        "electionTimeoutMillis" : 10000,
        "catchUpTimeoutMillis" : -1,
        "catchUpTakeoverDelayMillis" : 30000,
        "getLastErrorModes" : {

        },
        "getLastErrorDefaults" : {
            "w" : 1,
            "wtimeout" : 0
        },
        "replicaSetId" : ObjectId("6051ca21a1f8138a01c3b940")
    }
}
handong1:PRIMARY> cfg.members[3].priority=0
0
handong1:PRIMARY> rs.reconfig(cfg)
{
    "ok" : 1,
    "$clusterTime" : {
        "clusterTime" : Timestamp(1618225566, 2),
        "signature" : {
            "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
            "keyId" : NumberLong(0)
        }
    },
    "operationTime" : Timestamp(1618225566, 2)
}

查看修改完之后状态:

handong1:PRIMARY> rs.config()
{
    "_id" : "handong1",
    "version" : 20,
    "protocolVersion" : NumberLong(1),
    "writeConcernMajorityJournalDefault" : true,
    "members" : [
        {
            "_id" : 0,
            "host" : "172.16.254.131:27017",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 2,
            "tags" : {

            },
            "slaveDelay" : NumberLong(0),
            "votes" : 1
        },
        {
            "_id" : 1,
            "host" : "mongo2:27017",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 1,
            "tags" : {

            },
            "slaveDelay" : NumberLong(0),
            "votes" : 1
        },
        {
            "_id" : 2,
            "host" : "mongo3:27017",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 1,
            "tags" : {

            },
            "slaveDelay" : NumberLong(0),
            "votes" : 1
        },
        {
            "_id" : 3,
            "host" : "mongo4:27017",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 0,
            "tags" : {

            },
            "slaveDelay" : NumberLong(0),
            "votes" : 1
        }
    ],
    "settings" : {
        "chainingAllowed" : true,
        "heartbeatIntervalMillis" : 2000,
        "heartbeatTimeoutSecs" : 10,
        "electionTimeoutMillis" : 10000,
        "catchUpTimeoutMillis" : -1,
        "catchUpTakeoverDelayMillis" : 30000,
        "getLastErrorModes" : {

        },
        "getLastErrorDefaults" : {
            "w" : 1,
            "wtimeout" : 0
        },
        "replicaSetId" : ObjectId("6051ca21a1f8138a01c3b940")
    }
}

可以看到_id为3的secondary节点已经修改为0。