Upgrading Cluster shards tinto ReplicaSets shards.

[Erez Zarum]

Hello,
I have 3 shards servers in a cluster, those shards server currently do
not have any replicasets configured.
I would like to upgrade them with replicasets.

for that i shutdown the whole cluster and started them with --replSet.
I also added another members and an arbiter.
This is the current configuration:
config0 - localhost:20000
mongos - localhost:27017
shard0 - localhost:10000 / replSet - localhost:10010 / arbiter -
localhost:10020
shard1 - localhost:10001 / replSet - localhost:10011 / arbiter -
localhost:10021
shard2 - localhost:10002 / replSet - localhost:10012 / arbiter -
localhost:10022

All work well between them, the failover works, but the real problem is
in the cluster.
because the cluster does not know that those shards are replicasets.

If i had built the cluster from scratch with those replicasets i know i
would have used: db.runCommand({ addshard : shard0/localhost:10000}); to
add a replicaset named shard0 to the cluster.
This will not work because the cluster already knows localhost:10000 and
i get an error
"can't add shard shard0/localhost:10000 because a local database
'shardDb' exists in another shard0000:localhost:10000

How can i modify the cluster configuration so it will be aware those
shards have replicasets?

Thanks!

[Scott Hernandez]

The thing that strikes about this is that you really shouldn't be
using localhost (esp. for production systems). Why add more instances
on the same machine?

Is this a test configuration? If not, this seems like a bad idea.

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[Erez Zarum]

Correct, this is a test configuration only.

[Eliot Horowitz]

You would have to modify the config by hand, so great care must be used :)
You need to take down mongos, and edit the config db directly. The
shards collection specifically, and put it in the replset info
<name>/server1,server2

[Erez Zarum]

Hey,
Thanks for your reply,
How would one do that?
Is there any documentation on that?

Thanks!!

[Eliot Horowitz]

No documentation per se, but if you look at the config db, it should
pretty obvious.
Its a regular mongo collection, so you would just do an update() with
the shard name.
If you send db.shards.find() output, we can check you've got it right.

[Erez Zarum]

As example:
# mongo
MongoDB shell version: 1.6.5
connecting to: test
> use config
switched to db config
> db.shards.find();
{ "_id" : "shard0000", "host" : "localhost:10001" }
{ "_id" : "shard0001", "host" : "localhost:10002" }
{ "_id" : "shard0002", "host" : "localhost:10003" }
{ "_id" : "shard0", "host" : "shard0/localhost:10000" }

[Ofer Fort]

Is this only because the test env is on one server? Will this be any
different, in production when each shard is on it's own machine

[Eliot Horowitz]

@ofer Not sure what you mean.
I would never recommend going into production with a single node
shard, so you should really never get into this state for real.

[Erez Zarum]

How would i update the config database?
You are also writing: <name>/server1,server2, isn't it supposed to be
name/server1?
"If the individual shards consist of replica sets, they can be added by
specifying
replicaSetName/<serverhostname>[:port][,serverhostname2[:port],...],
where at least one server in the replica set is given."
So, everytime i add a new ReplicaSet member into the shard i need to
update the config server?

> db.shards.find();
{ "_id" : "shard0000", "host" : "localhost:10001" }
{ "_id" : "shard0001", "host" : "localhost:10002" }
{ "_id" : "shard0002", "host" : "localhost:10003" }
{ "_id" : "shard0", "host" : "shard0/localhost:10000" }

That's my config server, i have shutdown mongos and connect directly to
the config server.

Thanks!

[Erez Zarum]

I think i figured out myself, please correct me if anything is wrong,
The shard i want to add have a replSetName "shard1", if i update the
config db i must retain the name of the previous shard as id (shard0000)
but the host should be shard1/localhost:10001.

example:

> db.shards.update( { _id: "shard0000" }, { _id: "shard1", "host" :
"shard1/localhost:10001" });
> db.shards.find();

{ "_id" : "shard0001", "host" : "localhost:10002" }
{ "_id" : "shard0002", "host" : "localhost:10003" }
{ "_id" : "shard0", "host" : "shard0/localhost:10000" }

{ "_id" : "shard1", "host" : "shard1/localhost:10001" }

mongos fails here.., he can't find shard0000 while doing a balance.

> db.shards.update({ _id : "shard0000" }, { _id : "shard0000", "host" :
"shard1/localhost:10001" });
> db.shards.find();

{ "_id" : "shard0001", "host" : "localhost:10002" }
{ "_id" : "shard0002", "host" : "localhost:10003" }
{ "_id" : "shard0", "host" : "shard0/localhost:10000" }

{ "_id" : "shard0000", "host" : "shard1/localhost:10001" }

mongos works, he can find shard0000 and also know it's a replicaset,
shard1/localhost...
Fri Jan 14 11:30:24 [Balancer] updated set to:
shard1/localhost:10001,localhost:10011

Correct?

[Kristina Chodorow]

Yes, if it knows it's a replica set, it'll update its configuration as the set changes.