Vryjdfkk

I have a mongo cluster which includes

one "mongos"

one "config" (rscfg/a.a.a.a:27019)

two "shard"

Here is the situation, I added a new rs on config server and remove the old one

rs.add("b.b.b.b:27019")

and that's OK , when I look rs config it shows

rscfg/a.a.a.a:27019,b.b.b.b:27019

and than I remove the old machine (because the server needs to be upgraded)

rs.remove("a.a.a.a:27019")

also it's OK. and the production service without any connection issue.

I think the shard cluster connect to the new configdb server successfully.

then, I restarted shard cluster , and something goes wrong.

the shard server log says it cannot connect to "rscfg/c.c.c.c:27019" which is no longer exists.

It's old setting . even I add a.a.a.a:27019 back, doesn't help.....

It connected to a server(c.c.c.c) which is removed long time ago...

I have two questions.

1.How to change the configDB list in shard cluster directly?

2.How to list all configDB which shard cluster "really use"?

I've used db.runCommand("getShardMap")
it shows

"rscfg/b.b.b.b:27019"

and it connect to "rscfg/c.c.c.c:27019" What the hell?????

BTW, I used iptable to walkaround this problem.

iptables -t nat -A OUTPUT -p tcp -d c.c.c.c --dport 27019 -j DNAT --to-destination b.b.b.b:27019

How to reconfig config server connection setting from shard cluster?

As per MongoDB BOL documentation here you shall find the steps to Replace a Config Server.

Start the replacement config server

mongod --configsvr --replSet <replicaSetName> --bind_ip localhost,<ip address of the mongod host>

Add the new config server to the replica set

rs.add( { host: "<hostnameNew>:<portNew>", priority: 0, votes: 0 } )

Update the newly added config server’s votes and priority settings

Ensure that the new member has reached SECONDARY state. To check the state of the replica set members, run rs.status():

 rs.status()

Reconfigure the replica set to update the votes and priority of the new member:

var cfg = rs.conf();



cfg.members[n].priority = 1;  // Substitute the correct array index for the new member

cfg.members[n].votes = 1;     // Substitute the correct array index for the new member



rs.reconfig(cfg)

Shut down the member to replace

If replacing the primary member, step down the primary first before shutting down.

Remove the member to replace from the config server replica set

rs.remove("<hostnameOld>:<portOld>")

If necessary, update mongos configuration or DNS entry

With replica set config servers, the mongos instances specify in the --configdb or sharding.configDB setting the config server replica set name and at least one of the replica set members.

a mongos instance specified the removed member in the --configdb or configDB setting, either:

• Update the setting for the next time you restart the mongos, or




• Modify the DNS entry that points to the system that provided the old
  config server, so that the same hostname points to the new config
  
  server.

How to change the configDB list in shard cluster directly?

Specify the config server replica set name and the hostname and port of at least one of the members of the config server replica set.

sharding:

  configDB: <configReplSetName>/cfg1.example.net:27017, cfg2.example.net:27017,...

How to list all configDB which shard cluster "really use"?

To list the databases that have sharding enabled, query the databases collection in the Config Database. A database has sharding enabled if the value of the partitioned field is true. Connect to a mongos instance with a mongo shell, and run the following operation to get a full list of databases with sharding enabled:

use config

db.databases.find( { "partitioned": true } )

Example

You can use the following sequence of commands to return a list of all databases in the cluster:

use config

db.databases.find()







{ "_id" : "test", "primary" : "shardB", "partitioned" : false }

{ "_id" : "animals", "primary" : "shardA", "partitioned" : true }

{ "_id" : "farms", "primary" : "shardA", "partitioned" : false }

Then sharding is only enabled for the animals database.