Testing mongo replication on OSX - mongodb

Question

In two different terminals, I start up mongod with:
mongod --dbpath 1 --port 27001 --smallfiles --oplogSize 50 --logpath log.1 --replSet test
mongod --dbpath 2 --port 27002 --smallfiles --oplogSize 50 --logpath log.2 --replSet test
(data subdirectories 1 and 2 already created).
I go into a third window and run the mongo shell against one of the mongod instances
mongo --port 27001
In the shell, I setup a configuration as
cfg = { _id: "test", members: [ {_id:0, host: "localhost:27001"}, {_id:1, host:"localhost:27002"} ] }
then run:
use admin
rs.initiate(cfg)
The response from the shell is:
{
"startupStatus" : 4,
"info" : "hotest",
"errmsg" : "all members and seeds must be reachable to initiate set",
"ok" : 0
}
The logfile for instance on port 27001 reports:
Sun Nov 18 18:32:56 [rsStart] trying to contact macbookpro.local:27001
Sun Nov 18 18:32:56 [rsStart] couldn't connect to macbookpro.local:27001: couldn't connect to server macbookpro.local:27001
Sun Nov 18 18:32:56 [rsStart] replSet can't get local.system.replset config from self or any seed (yet)
It appears that the rs.initiate(cfg) cannot connect to the mongod instance on port 27001. But when I run mongod without --replSet the mongo shell connects just fine.
It isn't clear where I am screwing up but I will bet it is obvious.

Answer 1

Found it!
It turns out that when one installs MongoDB on OSX with brew a configuration file is created at /usr/local/etc/mongo.conf. In this file there was the line:
# Only accept local connections
bind_ip = 127.0.0.1
Well, if you look at the log the rsStart error was:
Sun Nov 18 18:32:56 [rsStart] trying to contact macbookpro.local:27001
Sun Nov 18 18:32:56 [rsStart] couldn't connect to macbookpro.local:27001: couldn't connect to server macbookpro.local:27001
Sun Nov 18 18:32:56 [rsStart] replSet can't get local.system.replset config from self or any seed (yet)
and if I ping macbookpro.local the IP address returned was 192.168.41.1. 192.168.41.1 <> 127.0.0.1 so mongod was refusing to respond. Removing this line from the configuration allowed be to setup replication successfully.
sheesh. I am such an idiot. Looked for hours at this and kept thinking that the machine name when connected to the network was 127.0.0.1. Let this be a lesson to you---don't get old!

Answer 2

Figuring out the hostnames can be painful, so instead of passing the config object and trying to work out what your hostname should be, just do rs.initiate() with no arguments on the first host. That will create the required config, discovering the correct value for you. It will print out the "valid" version of the config that it created. Here's a sample:
> rs.initiate()
{
"info2" : "no configuration explicitly specified -- making one",
"me" : "adamc-mbp.local:27001",
"info" : "Config now saved locally. Should come online in about a minute.",
"ok" : 1
}
Copy and paste the "me" field and use the new port number, pass to rs.add():
sotest:PRIMARY> rs.add("adamc-mbp.local:27002")
{ "ok" : 1 }
Now take a look at your config:
sotest:PRIMARY> rs.conf()
{
"_id" : "sotest",
"version" : 2,
"members" : [
{
"_id" : 0,
"host" : "adamc-mbp.local:27001"
},
{
"_id" : 1,
"host" : "adamc-mbp.local:27002"
}
]
}
You should be good to go :)

Answer 3

I had the same issue. Somehow mongo resolves localhost as your machine's name macbookpro.local.
Just add this line to your /etc/hosts file :
127.0.0.1 macbookpro.local