adding and removing a node from a mongo replica set

Question

I have a new backup server I want to add to our mongo replica sets. As far as I can tell its as easy as logging on to the replica sets primary and adding the following command:

rs.add( { host: "mongobackup:10003", priority: 0, votes: 0, hidden: true } )

My understanding is that after doing so the primary should sync all its configuration and data with the new node.

Additionally I have an old backup server I want to remove from the replica set which I looks like all i have to do is type this command into the replica sets primary:

rs.remove( "oldmongobackup:10003" )

Is there anything else I am missing?

rs2:PRIMARY> rs.conf()
{
    "_id" : "rs2",
    "version" : 26,
    "members" : [
        {
            "_id" : 7,
            "host" : "mongo03:10001",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 20,
            "tags" : {
                "dc" : "maid"
            },
            "slaveDelay" : 0,
            "votes" : 1
        },
        {
            "_id" : 8,
            "host" : "mongo01:10002",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 10,
            "tags" : {
                "dc" : "maid"
            },
            "slaveDelay" : 0,
            "votes" : 1
        },
        {
            "_id" : 9,
            "host" : "mongo02:10003",
            "arbiterOnly" : true,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 1,
            "tags" : {

            },
            "slaveDelay" : 0,
            "votes" : 1
        },
        {
            "_id" : 10,
            "host" : "oldmongobackup:10003",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : true,
            "priority" : 0,
            "tags" : {

            },
            "slaveDelay" : 0,
            "votes" : 1
        }
    ],
    "settings" : {
        "chainingAllowed" : true,
        "heartbeatTimeoutSecs" : 10,
        "getLastErrorModes" : {

        },
        "getLastErrorDefaults" : {
            "w" : 1,
            "wtimeout" : 0
        }
    }
}

Answer 1

The command should be fine to run. Why ???

Each rs.add() and rs.remove() should trigger an election. Since the priorities of the remaining nodes have unique values:

• _id : 7 as priority : 20
• _id : 8 as priority : 10
• _id : 9 as priority : 1

you can say the election is rigged. The primary node should remain the primary.