Creating mongo 3 node replica set on ec2 problems I'm trying to create a 3 node cluster of mongo replicas on ec2 instances, with internal ips 10.168.xxx.xxx, 10.166.xxx.xxx and 10.188.xxx.xxx, my config file is:

dbpath = /home/ubuntu/mongo-data/
logpath = /home/ubuntu/mongo-data/mongod.log
logappend = true

journal = true
fork = true
smallfiles = true
pidfilepath = /home/ubuntu/mongo-data/mongod.pid
replSet = appNameReplicaSet


I launched mongod -f mongod.config on each instance, and on one of those I tried:

$ mongo
&gt; rs.initiate();
{
"info2" : "no configuration explicitly specified -- making one",
"me" : "ip-10-168-66-132:27017",
"info" : "Config now saved locally.  Should come online in about a minute.",
"ok" : 1
}
&gt; rs.add('10.166.xxx.xxx:27017');
//after LONG pause
{
"errmsg" : "exception: need most members up to reconfigure, not ok : 10.188.22.254:27017",
"code" : 13144,
"ok" : 0
}


I also tried:

config = {
    _id: 'appNameReplicaSet',
        members: [
        {_id: 0, host: '10.168.xxx.xxx:27017'},
        {_id: 1, host: '10.166.xxx.xxx:27017'},
        {_id: 2, host: '10.188.xxx.xxx:27017'}
    ]
}
rs.reconfig(config, {'force':true})
{ "ok" : 0, "errmsg" : "a replSetReconfig is already in progress" }


.log file:

Sat Jul 27 01:33:59.149 [initandlisten] connection accepted from 127.0.0.1:36931 #4 (1 connection now open)
Sat Jul 27 01:34:02.468 [conn4] replSet replSetInitiate admin command received from client
Sat Jul 27 01:34:02.470 [conn4] replSet info initiate : no configuration specified.  Using a default configuration for the set
Sat Jul 27 01:34:02.470 [conn4] replSet created this configuration for initiation : { _id: "appNameReplicaSet", members: [ { _id: 0, host: "ip-10-168-xxx-xxx:27017" } ] }
Sat Jul 27 01:34:02.470 [conn4] replSet replSetInitiate config object parses ok, 1 members specified
Sat Jul 27 01:34:02.473 [conn4] replSet replSetInitiate all members seem up
Sat Jul 27 01:34:02.473 [conn4] ******
Sat Jul 27 01:34:02.473 [conn4] creating replication oplog of size: 990MB...
Sat Jul 27 01:34:02.474 [FileAllocator] allocating new datafile /home/ubuntu/mongo-data/local.1, filling with zeroes...
Sat Jul 27 01:34:02.485 [FileAllocator] done allocating datafile /home/ubuntu/mongo-data/local.1, size: 511MB,  took 0.01 secs
Sat Jul 27 01:34:02.485 [FileAllocator] allocating new datafile /home/ubuntu/mongo-data/local.2, filling with zeroes...
Sat Jul 27 01:34:02.491 [FileAllocator] done allocating datafile /home/ubuntu/mongo-data/local.2, size: 511MB,  took 0.005 secs
Sat Jul 27 01:34:02.491 [conn4] ******
Sat Jul 27 01:34:02.491 [conn4] replSet info saving a newer config version to local.system.replset
Sat Jul 27 01:34:02.492 [conn4] replSet saveConfigLocally done
Sat Jul 27 01:34:02.492 [conn4] replSet replSetInitiate config now saved locally.  Should come online in about a minute.
Sat Jul 27 01:34:08.435 [rsStart] replSet I am ip-10-168-xxx-xxx:27017
Sat Jul 27 01:34:08.435 [rsStart] replSet STARTUP2
Sat Jul 27 01:34:09.441 [rsSync] replSet SECONDARY
Sat Jul 27 01:34:09.441 [rsMgr] replSet info electSelf 0
Sat Jul 27 01:34:10.440 [rsMgr] replSet PRIMARY
Sat Jul 27 01:34:26.513 [conn4] replSet replSetReconfig config object parses ok, 2 members specified
Sat Jul 27 01:37:45.835 [conn4] couldn't connect to 10.188.xxx.xxx:27017: couldn't connect to server 10.188.xxx.xxx:27017


UPDATE: added output of rs.initiate() &amp; logs;
This is probably a firewall issue. The long pause is the socket connection hanging while it waits for it to timeout.

By default on EC2 the security groups (eg. firewall rules) for instances deny all inbound traffic. You have to explicitly specify what IP ranges or security group members are allowed to connect.

Using security groups instead of IPs is generally more maintainable. It allows you to add/remove additional servers later without worrying about updating the IP addresses that get dynamically assigned. You just need to include them in the same security group.

To get setup:


Create a security group specifically for your MongoDB instances. Let's call it "My MongoDB SG" and assume that AWS gives it the unique id sg-123456.
Edit the inbound firewall rules for the security group to allow traffic from the same security group on port. The entry should look like:

 Source         Port
 sg-123456      27017

Add the security group to each of your MongoDB instances


Then you can retry starting up the cluster.