MongoDB for Oracle DBA’s Part 6 : Creating a Shard for ReplicaSet in Standalone Server

In previous post we saw, to create a replicaset like standby in standalone server.

Basically with a replicaset the read/writes can be achieved via primary node and secondary nodes are inaccessible, this creates a concurrency issues with single node cluster. So we create a shard i.e data partitioning across nodes. The data will be distributed to shards , shard 1 with replicaset and to shard2 with replicaset.

To do this, we need

• The existing replicaset should be modified to enable sharding
• Create a mongoc instance , to store the metadata for data distribution for shard keys
• Create a mongos instance, to route the database requests to right shard

The steps broadly will be,

• Stop all the mongod instances
• Change the configuration file to add shardsvr = true
• Create config and mongos nodes
• Start the mongod instances in replicaset rs0
• Add the replicatset rs0 to a shard

###Stop all the mongod instances

mongod -f /backups/data/cluster/shard1/rs0.conf --shutdown

mongod -f /backups/data/cluster/shard1/rs1.conf --shutdown

mongod -f /backups/data/cluster/shard1/rs2.conf --shutdown

###Change the configuration file

vi /backups/data/cluster/shard1/rs0.conf

vi /backups/data/cluster/shard1/rs1.conf

vi /backups/data/cluster/shard1/rs2.conf

Append this line

sharding:

clusterRole: shardsvr

### Create Mongo config node by creating directories and configuration file

mkdir -p /backups/data/cluster/mongoc/logs

mkdir -p /backups/data/cluster/mongoc/data

vi /backups/data/cluster/mongoc/mongoc.conf

systemLog:

destination: file

path: "/backups/data/cluster/mongoc/logs/mongoc.log"

logAppend: true

processManagement:

pidFilePath: "/backups/data/cluster/mongoc/mongoc.pid"

fork: true

net:

bindIp: 127.0.0.1

port: 37019

storage:

engine: "wiredtiger"

dbPath: "/backups/data/cluster/mongoc/data"

directoryPerDB: true

sharding:

clusterRole: configsvr

operationProfiling:

mode: "all"

replication:

oplogSizeMB: 5120

replSetName: "crs0"

Note: the Port and Cluster role is configsvr and the directory path

### Create mongos instances configuration

mkdir -p /backups/data/cluster/mongos/logs

mkdir -p /backups/data/cluster/mongos/data

vi /backups/data/cluster/mongos/mongos.conf

systemLog:

destination: file

path: "/backups/data/cluster/mongos/logs/mongos.log"

logAppend: true

processManagement:

pidFilePath: "/backups/data/cluster/mongos/mongos.pid"

fork: true

net:

bindIp: 127.0.0.1

port: 27017

sharding:

configDB: "crs0/localhost:37019"

autoSplit: true

Note: For mongos instance it is wise to use 27017 a default port and look at configDB points to Mongo Config Server (port)

###Start the servers

###Firstly Start the mongod instances

mongod -f /backups/data/cluster/shard1/rs0.conf

mongod -f /backups/data/cluster/shard1/rs1.conf

mongod -f /backups/data/cluster/shard1/rs2.conf

###Start the mongod config server instance, from 3.4 onwards the config server must have replicaset enabled, hence we are adding replicaset with one node for development purpose.

mongod -f /backups/data/cluster/mongoc/mongoc.conf

mongo localhost:37019

rs.initiate({_id:"crs0", members: [{"_id":1, "host":"localhost:37019"}

###Start the mongos

mongos -f /backups/data/cluster/mongos/mongos.conf

### Finally , Add the replica set to shard

###Connect to mongos, where our mongos is running on port 27017

mongo localhost:27017

sh.addShard("rs0/localhost:47018,localhost:47019,localhost:47020");

###Enable the sharding for foo database

mongo localhost:27017

sh.enableSharding("mydb")

###Check the shard status

mongo localhost:27017

sh.status()

--- Sharding Status ---

sharding version: {

"_id" : 1,

"minCompatibleVersion" : 5,

"currentVersion" : 6,

"clusterId" : ObjectId("5834e646a2c25f3b06d65226")

}

shards:

{ "_id" : "rs0", "host" : "rs0/localhost:47018,localhost:47019,localhost:47020" }

active mongoses:

"3.2.1" : 1

balancer:

Currently enabled: yes

Currently running: no

Failed balancer rounds in last 5 attempts: 0

Migration Results for the last 24 hours:

No recent migrations

databases:

{ "_id" : "foo", "primary" : "rs0", "partitioned" : true }

The above shows that the replicaset rs0 is a shard and this cluster has only single shard with database foo sharding is enabled.

Next Post , Adding a New Shard in standalone server

-Thanks

GeekDBA