Mongodb – mongo replication not happening

mongodb

I setup master/slave replication of mongodb on EC2. But I see not replication happening. When I do "show dbs" on master, it shows all dbs expected.

But when I do the same on replica, it does not show me any db.

Please help me troubleshoot.

rs.config()
{
    "_id" : "ittw",
    "version" : 1,
    "members" : [
        {
            "_id" : 0,
            "host" : "ip-10-304-48-93:27017"
        }
    ]
}

rs.config()
{
    "_id" : "ittw",
    "version" : 2,
    "members" : [
        {
            "_id" : 0,
            "host" : "domU-17-31-19-16-88-5F:27017"
        },
        {
            "_id" : 1,
            "host" : "ec2-50-321-52-908.compute-1.amazonaws.com:27017"
        }
    ]
}



rs.status() // replica
{
    "set" : "ittw",
    "date" : ISODate("2013-08-12T06:55:57Z"),
    "myState" : 1,
    "members" : [
        {
            "_id" : 0,
            "name" : "$ip:27017",
            "health" : 1,
            "state" : 1,
            "stateStr" : "PRIMARY",
            "uptime" : 356039,
            "optime" : Timestamp(1375934685, 1),
            "optimeDate" : ISODate("2013-08-08T04:04:45Z"),
            "self" : true
        }
    ],
    "ok" : 1
}



rs.status()  //Master
{
    "set" : "ittw",
    "date" : ISODate("2013-08-12T06:57:19Z"),
    "myState" : 1,
    "members" : [
        {
            "_id" : 0,
            "name" : "PRI_IP:27017",
            "health" : 1,
            "state" : 1,
            "stateStr" : "PRIMARY",
            "uptime" : 356543,
            "optime" : Timestamp(1376289725, 1),
            "optimeDate" : ISODate("2013-08-12T06:42:05Z"),
            "self" : true
        },
        {
            "_id" : 1,
            "name" : "REP_IP:27017",
            "health" : 1,
            "state" : 1,
            "stateStr" : "PRIMARY",
            "uptime" : 355869,
            "optime" : Timestamp(1375934685, 1),
            "optimeDate" : ISODate("2013-08-08T04:04:45Z"),
            "lastHeartbeat" : ISODate("2013-08-12T06:57:17Z"),
            "lastHeartbeatRecv" : ISODate("1970-01-01T00:00:00Z"),
            "pingMs" : 1
        }
    ],
    "ok" : 1
}

Best Answer

It looks like what you have done is run rs.initiate() on both the primary and the secondary server.

In this case the outcome is that you have two different replica sets called ittw rather than a single replica set with replication. The primary knows about both nodes, but the "secondary" you setup is also configured as a primary for a replica set only containing itself. This definitely won't work.

As per the instructions on Deploying a replica set, you should only run rs.initiate() on the primary, and then use rs.add("hostname:port") to add secondaries to the same replica set.

To fix up your dud secondary to a clean state, you should:

  • stop the secondary using db.shutdownServer() or appropriate command like service mongodb stop (depending on how you installed MongoDB)
  • remove the files in the dbpath directory for the secondary
  • restart the secondary
  • use the mongo shell to connect to the primary, and rs.add() your secondary

If all is well you should see consistent rs.status() information on the primary and new secondary.

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