Connecting to a replica set with mongo CLI

[aharbick]

Is there a way to connect to a mongo replica set through the mongo
CLI? For example I've got a replica set with three replicas. If I
do:
mongo myhost1.com/my_database

it'll connect but a command like "show tables" will trigger:
Tue Jan 18 14:24:51 uncaught exception: error: { "$err" : "not
master", "code" : 10107 }

I've monkeyed around with specifying multiple hosts e.g.:
mongo myhost1.com/my_database,myhost2.com/my_database,myhost3.com/
my_database
mongo -h myhost1.com,myhost2.com,myhost3.com my_database
etc.

but I get warnings that imply I'm not doing something right. Is this
possible?

[Scott Hernandez]

The javascript shell is meant to connect to any specific host. It will
not connect to the primary/master node of the replicaset
automatically, like some drivers will do.

You should just connect to the primary (master) directly.

If you want to run queries on secondaries (not-master) then you must
set slaveOk.
> db.getMongo().setSlaveOk()

You can also get help:
> help
> rs.help()

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[aharbick]

> The javascript shell is meant to connect to any specific host. It will
> not connect to the primary/master node of the replicaset
> automatically, like some drivers will do.

I figured that.

> You should just connect to the primary (master) directly.

That's the problem. Generally I know what the master is but when it
switches around (say one of the replicas bounces) then I have to play
a guessing game.

>
> If you want to run queries on secondaries (not-master) then you must
> set slaveOk.
>
> > db.getMongo().setSlaveOk()

Yeah, that's probably a good solution for most of my use cases.

Thanks!
Andy

[Scott Hernandez]

On Tue, Jan 18, 2011 at 12:11 PM, aharbick <ahar...@gmail.com> wrote:
>> The javascript shell is meant to connect to any specific host. It will
>> not connect to the primary/master node of the replicaset
>> automatically, like some drivers will do.
>
> I figured that.
>
>> You should just connect to the primary (master) directly.
>
> That's the problem.  Generally I know what the master is but when it
> switches around (say one of the replicas bounces) then I have to play
> a guessing game.

You can write a script to get the master fairly easily. That is what
the drivers do:
http://www.mongodb.org/display/DOCS/Replica+Set+Commands#ReplicaSetCommands-Commands

Just write a shell script that does that call from a seed server/list
and starts mongo with the primary host.

You could also ask for a feature in the shell for this...
http://jira.mongodb.org/

>> If you want to run queries on secondaries (not-master) then you must
>> set slaveOk.
>>
>> > db.getMongo().setSlaveOk()
>
> Yeah, that's probably a good solution for most of my use cases.
>
> Thanks!
> Andy
>

[Wade Kaple]

I was having a similar issue, but in the context of automated deployments.  In order to not have to double check for the primary, I created a findMaster.js file that I pass into the shell before the script that I am trying to execute.  Contents of the file (check if this is primary, otherwise connect to primary):

var master = db.isMaster();

if (master.ismaster == false)

{

  db = connect(master.primary + '/' + db);

}

Then just call the shell with this file first:

mongo <address>/<db> findMaster.js <scriptToExec>.js

The reassignment of the db variable is then available to the second script.

[Asya Kamsky]

Wade,

The problem with commenting on extremely old threads is that you might miss that the shell now has ability to connect to a replica set (and reconnect to primary automatically).

Just use

'mongo -host replSetName/host:port'   where you would use your replica set name and give one of the hosts that's currently up - the shell will figure out the rest.

Asya

[Cindy Conway]

Perfect. This was just what I was looking for. Thank you Asya.