MongoDB Replicaset Connection string using C# Driver

Question

I have My Mongo DB set with a replica set of 3. One Primary and Two secondaries.

 var connectionString = ConfigurationManager.AppSettings["MongoDBWriteCS"];
 var client = new MongoClient(connectionString);
 _MongoWriteServer = client.GetServer();
 _WriteDatabase = _MongoWriteServer.GetDatabase("DBName");
_WriteDatabase.GetCollection<CollectionType>("CollectionName").Insert(Object);

When my code runs with the below connection string, it has no issues to insert records

<add key="MongoDBWriteCS" value="mongodb://username:password@10.0.0.0:27019/admin?w=0" />

But the problem is, since it is on replica set, my primary keeps changing when primary goes from 27019 to 27018 or 27017 inserts fails.

So I tried to change my connection string as more authentic Replica set connection string.

<add key="MongoDBWriteCS" value="mongodb://username:password@10.0.0.0:27017,10.0.0.0:27018,10.0.0.0:27019/admin?replicaSet=myRepSet&amp;readPreference=primaryPreferred&amp;w=0" />

It keeps failing with " No such host " or " unable to connect to a member ",but with in the same line of code get list of collections works (I mean reads works only writes fails like insert or save commands)

I am using MongoDB 2.6.4

rs.status()

/* 0 */
{
    "set" : "rbRepSet",
    "date" : ISODate("2015-03-09T23:27:17.000Z"),
    "myState" : 1,
    "members" : [ 
        {
            "_id" : 0,
            "name" : "haboMongo:27017",
            "health" : 1,
            "state" : 2,
            "stateStr" : "SECONDARY",
            "uptime" : 59570,
            "optime" : Timestamp(1425941592, 5),
            "optimeDate" : ISODate("2015-03-09T22:53:12.000Z"),
            "lastHeartbeat" : ISODate("2015-03-09T23:27:16.000Z"),
            "lastHeartbeatRecv" : ISODate("2015-03-09T23:27:17.000Z"),
            "pingMs" : 0,
            "syncingTo" : "haboMongo:27019"
        }, 
        {
            "_id" : 1,
            "name" : "haboMongo:27018",
            "health" : 1,
            "state" : 2,
            "stateStr" : "SECONDARY",
            "uptime" : 2220179,
            "optime" : Timestamp(1425941592, 5),
            "optimeDate" : ISODate("2015-03-09T22:53:12.000Z"),
            "lastHeartbeat" : ISODate("2015-03-09T23:27:17.000Z"),
            "lastHeartbeatRecv" : ISODate("2015-03-09T23:27:16.000Z"),
            "pingMs" : 0,
            "syncingTo" : "haboMongo:27019"
        }, 
        {
            "_id" : 2,
            "name" : "haboMongo:27019",
            "health" : 1,
            "state" : 1,
            "stateStr" : "PRIMARY",
            "uptime" : 2220202,
            "optime" : Timestamp(1425941592, 5),
            "optimeDate" : ISODate("2015-03-09T22:53:12.000Z"),
            "electionTime" : Timestamp(1425100988, 1),
            "electionDate" : ISODate("2015-02-28T05:23:08.000Z"),
            "self" : true
        }
    ],
    "ok" : 1
}

rs.config()

/* 0 */
{
    "_id" : "rbRepSet",
    "version" : 3,
    "members" : [ 
        {
            "_id" : 0,
            "host" : "haboMongo:27017"
        }, 
        {
            "_id" : 1,
            "host" : "haboMongo:27018"
        }, 
        {
            "_id" : 2,
            "host" : "haboMongo:27019"
        }
    ]
}

Answer 1

Because you have used hostnames in your replica set configuration, the driver will discover those hostnames and use them instead of the ip addresses in your connection string. Therefore, your hostnames MUST be resolvable by your client box. I'd recommend you use hostnames, but if for some reason you can't, then you'll need to put IP addresses into your replica set config.