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Convert a Replica Set to a Sharded Cluster

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  • About This Task
  • Before You Begin
  • Steps
  • Learn More

Sharded clusters partition data across multiple servers based on a shard key. A sharded cluster scales better than a replica set for deployments with large data sets and high throughput operations.

This tutorial converts a single three-member replica set to a sharded cluster with two shards. Each shard in the new cluster is an independent three-member replica set.

You can convert to a sharded cluster in the UI for deployments hosted in MongoDB Atlas.

This tutorial uses the following servers:

Hostname
Port
Description
mongodb0.example.net
27017
Member of the initial data-bearing shard, rs0.
mongodb1.example.net
27017
Member of the initial data-bearing shard, rs0.
mongodb2.example.net
27017
Member of the initial data-bearing shard, rs0.
mongodb3.example.net
27018
Member of the second data-bearing shard, rs1.
mongodb4.example.net
27018
Member of the second data-bearing shard, rs1.
mongodb5.example.net
27018
Member of the second data-bearing shard, rs1.
mongodb6.example.net
27017
The mongos, used to connect to the sharded cluster.
mongodb7.example.net
27019
Member of the config server replica set.
mongodb8.example.net
27019
Member of the config server replica set.
mongodb9.example.net
27019
Member of the config server replica set.

The hostnames used in this tutorial are examples. Replace the hostnames used in the example commands with the hostnames used in your deployments.

Important

To avoid configuration updates due to IP address changes, use DNS hostnames instead of IP addresses. It is particularly important to use a DNS hostname instead of an IP address when configuring replica set members or sharded cluster members.

Use hostnames instead of IP addresses to configure clusters across a split network horizon. Starting in MongoDB 5.0, nodes that are only configured with an IP address fail startup validation and do not start.

To get existing users and roles, run mongodump:

mongodump -d=admin --out=adminDump -u <adminUser> -p <password> --host <replicaSetURI> --dumpDbUsersAndRoles

Deploy a three-member replica set for the config servers. In this example, the config servers use the following hosts:

  • mongodb7.example.net

  • mongodb8.example.net

  • mongodb9.example.net

1

Configure a mongod instance on each config server host. Specify these options in the configuration file for each mongod instance:

Option
Value
configReplSet
configsvr
localhost, followed by any other hostnames on which the mongod should listen for client connections.
replication:
replSetName: configReplSet
sharding:
clusterRole: configsvr
net:
bindIp: localhost,<hostname(s)>

Include additional options as appropriate for your deployment.

2

Deploy the mongod with your specified configuration:

mongod --config <PATH_TO_CONFIG_FILE>

The config servers use the default data directory /data/configdb and the default port 27019.

3

Use mongosh to connect to one of the config servers. For example:

mongosh "mongodb://mongodb7.example.net:27019"
4

To initiate the replica set, run rs.initiate():

rs.initiate( {
_id: "configReplSet",
configsvr: true,
members: [
{ _id: 0, host: "mongodb7.example.net:27019" },
{ _id: 1, host: "mongodb8.example.net:27019" },
{ _id: 2, host: "mongodb9.example.net:27019" }
]
} )

The preceding command uses the localhost exception to perform administrative actions without authentication.

Important

Run rs.initiate() on just one and only one mongod instance for the replica set.

Restore the existing users and roles you got when you ran mongodump.

mongorestore ./adminDump --nsInclude "admin.*" --host <configPrimaryURI>

The preceding command uses the localhost exception to perform administrative actions without authentication.

The output from running this command may be similar to:

0 document(s) restored successfully

This message does not indicate a problem. This output means that 0 documents other than the users and roles were restored.

Reconfigure and restart the config server replica set.

1

Select the tab for your authentication mechanism:

Restart a mongod instance on each of these hosts:

  • mongodb7.example.net

  • mongodb8.example.net

  • mongodb9.example.net

Specify these options in the configuration file for each mongod instance:

Option
Value
The path to the key file used for your initial replica set.
security:
keyFile: <PATH_TO_KEYFILE>
replication:
replSetName: configReplSet
sharding:
clusterRole: configsvr
net:
bindIp: localhost,<hostname(s)>

Include additional options as appropriate for your deployment.

Restart a mongod instance on each of these hosts:

  • mongodb7.example.net

  • mongodb8.example.net

  • mongodb9.example.net

Specify these options in the configuration file for each mongod instance in addition to the options you already configured:

Option
Value
x509
requireTLS
The absolute path to the .pem file that contains both the TLS certificate and key.
The absolute path to the .pem file that contains the root certificate chain from the Certificate Authority.

localhost, followed by any other hostnames on which the mongod should listen for client connections.

Warning

Before you bind your instance to a publicly-accessible IP address, you must secure your cluster from unauthorized access. For a complete list of security recommendations, see Security Checklist. At minimum, consider enabling authentication and hardening network infrastructure.

sharding:
clusterRole: configsvr
replication:
replSetName: configReplSet
security:
clusterAuthMode: x509
net:
tls:
mode: requireTLS
certificateKeyFile: <FILE_WITH_COMBINED_CERT_AND_KEY>
CAFile: <CA_FILE>
bindIp: localhost,<hostname(s)>

Include additional options as appropriate for your deployment, such as net.tls.certificateKeyFilePassword if your TLS certificate-key file is encrypted with a password.

2

Restart the mongod with your specified configuration:

mongod --config <PATH_TO_CONFIG_FILE> --shutdown
mongod --config <PATH_TO_CONFIG_FILE>

The mongos provides the interface between the client applications and the sharded cluster.

1

Specify these options in your mongos configuration file:

Option
Value
configReplSet, followed by a slash / and at least one of the config server hostnames and ports.
The path to the key file used for your initial replica set.
localhost, followed by any other hostnames on which the mongos should listen for client connections.
sharding:
configDB: configReplSet/mongodb7.example.net:27019,mongodb8.example.net:27019,mongodb9.example.net:27019
security:
keyFile: <PATH_TO_KEYFILE>
net:
bindIp: localhost,<hostname(s)>

Include additional options as appropriate for your deployment.

Specify these options in your mongos configuration file:

Option
Value
configReplSet, followed by a slash / and at least one of the config server hostnames and ports.
x509
requireTLS
The absolute path to the .pem file that contains both the TLS certificate and key.
The absolute path to the .pem file that contains the root certificate chain from the Certificate Authority.
localhost, followed by any other hostnames on which the mongos should listen for client connections.
sharding:
configDB: configReplSet/mongodb7.example.net:27019,mongodb8.example.net:27019,mongodb9.example.net:27019
security:
clusterAuthMode: x509
net:
tls:
mode: requireTLS
certificateKeyFile: <FILE_WITH_COMBINED_CERT_AND_KEY>
CAFile: <CA_FILE>
bindIp: localhost,<hostname(s)>

Include any additional options appropriate for your deployment.

2

Deploy the mongos with your specified configuration:

mongos --config <PATH_TO_CONFIG_FILE>

In this example, your initial replica set is a three-member replica set. This step updates the initial replica set so that it can be added as a shard to your sharded cluster.

The replica set runs on these hosts:

  • mongodb0.example.net:27017

  • mongodb1.example.net:27017

  • mongodb2.example.net:27017

For sharded clusters, you must set the role for each mongod instance in the shard to shardsvr. To specify the server role, set the sharding.clusterRole setting in the mongod configuration file.

Note

The default port for mongod instances with the shardsvr role is 27018. To use a different port, specify the net.port setting.

1

Use mongosh to connect to one of the members of your initial replica set.

mongosh "mongodb://<username>@mongodb0.example.net:27017"

If your deployment uses x.509 authentication, specify these mongosh options:

For example:

mongosh "mongodb://<username>@mongodb0.example.net:27017" --tls --tlsCAFile <CA_FILE> --tlsCertificateKeyFile <filename>
2

Run rs.status() to determine the primary and secondaries:

rs.status()

In the command output, the replSetGetStatus.members[n].stateStr field indicates which member is the primary and which members are secondaries.

3

Warning

This step requires some downtime for applications connected to the replica set secondaries.

After you restart a secondary, any applications that are connected to that secondary return a CannotVerifyAndSignLogicalTime error until you perform the steps in 7. Add the Initial Replica Set as a Shard.

You can also restart your application to stop it from receiving CannotVerifyAndSignLogicalTime errors.

1

Use mongosh to connect to one of the secondaries.

mongosh "mongodb://<username>@<host>:<port>"
2

Run the following commands:

use admin
db.shutdownServer()
3

In the secondary's configuration file, set sharding.clusterRole to shardsvr:

security:
keyFile: <PATH_TO_KEYFILE>
replication:
replSetName: rs0
sharding:
clusterRole: shardsvr
net:
port: 27017
bindIp: localhost,<hostname(s)>

Include additional options as appropriate for your deployment.

4

Run the following command on the host containing the secondary:

mongod --config <PATH_TO_CONFIG_FILE>
5
1

Use mongosh to connect to one of the secondaries.

If your deployment uses x.509 authentication, specify these mongosh options:

mongosh "mongodb://<username>@<host>:<port>" --tls --tlsCAFile <CA_FILE> --tlsCertificateKeyFile <filename>
2

Run the following commands:

use admin
db.shutdownServer()
3

In the secondary's configuration file, set sharding.clusterRole to shardsvr:

replication:
replSetName: rs0
sharding:
clusterRole: shardsvr
security:
clusterAuthMode: x509
net:
port: 27017
tls:
mode: requireTLS
certificateKeyFile: <FILE_WITH_COMBINED_CERT_AND_KEY>
CAFile: <CA_FILE>
bindIp: localhost,<hostname(s)>

Include additional options as appropriate for your deployment, such as net.tls.certificateKeyFilePassword if your TLS certificate-key file is encrypted with a password.

4

Run the following command on the host containing the secondary:

mongod --config <PATH_TO_CONFIG_FILE>
5
4

Warning

This step requires some downtime for applications connected to the primary of the replica set.

After you restart the primary, any applications that are connected to the primary return a CannotVerifyAndSignLogicalTime error until you perform the steps in 7. Add the Initial Replica Set as a Shard.

You can also restart your application to stop it from receiving CannotVerifyAndSignLogicalTime errors.

1

Use mongosh to connect to the primary:

mongosh "mongodb://<username>@<host>:<port>"
2

Run the following command:

rs.stepDown()
3

Run rs.status() to confirm that the member you are connected to has stepped down and is now a secondary:

rs.status()
4

Run the following commands:

use admin
db.shutdownServer()

Wait for the shutdown to complete.

5

In the primary's configuration file, set sharding.clusterRole to shardsvr:

security:
keyFile: <PATH_TO_KEYFILE>
replication:
replSetName: rs0
sharding:
clusterRole: shardsvr
net:
port: 27017
bindIp: localhost,<hostname(s)>

Include additional options as appropriate for your deployment.

6

Run the following command on the host containing the primary:

mongod --config <PATH_TO_CONFIG_FILE>
1

Use mongosh to connect to one of the secondaries.

If your deployment uses x.509 authentication, specify these mongosh options:

If your deployment uses x.509 authentication, specify these mongosh options:

mongosh "mongodb://<username>@<host>:<port>" --tls --tlsCAFile <CA_FILE> --tlsCertificateKeyFile <filename>
2

Run the following command:

rs.stepDown()
3

Run rs.status() to confirm that the member you are connected to has stepped down and is now a secondary:

rs.status()
4

Run the following commands:

use admin
db.shutdownServer()

Wait for the shutdown to complete.

5

In the primary's configuration file, set sharding.clusterRole to shardsvr:

replication:
replSetName: rs0
sharding:
clusterRole: shardsvr
security:
clusterAuthMode: x509
net:
port: 27017
tls:
mode: requireTLS
certificateKeyFile: <FILE_WITH_COMBINED_CERT_AND_KEY>
CAFile: <CA_FILE>
bindIp: localhost,<hostname(s)>

Include additional options as appropriate for your deployment, such as net.tls.certificateKeyFilePassword if your TLS certificate-key file is encrypted with a password.

6

Run the following command on the host containing the primary:

mongod --config <PATH_TO_CONFIG_FILE>

After you convert the initial replica set (rs0) to a shard, add it to the sharded cluster.

1

The mongos instance is running on host mongodb6.example.net.

To connect mongosh to the mongos, run the following command:

mongosh "mongodb://admin01@mongodb6.example.net:27017"

If your deployment uses x.509 authentication, specify these mongosh options:

If your deployment uses x.509 authentication, specify these mongosh options:

mongosh "mongodb://admin01@mongodb6.example.net:27017" --tls --tlsCAFile <CA_FILE> --tlsCertificateKeyFile <filename>

This command authenticates you as the admin01 user you created on the sharded cluster. After you enter the command, enter your user's password.

2

To add a shard to the cluster, run the sh.addShard() method:

sh.addShard( "rs0/mongodb0.example.net:27017,mongodb1.example.net:27017,mongodb2.example.net:27017" )

Warning

Once the new shard is active, mongosh and other clients must always connect to the mongos instance. Do not connect directly to the mongod instances. If your clients connect to shards directly, you may create data or metadata inconsistencies.

After you add the first shard to your cluster, update the connection string used by your applications to the connection string for your sharded cluster. Then, restart your applications.

Deploy a new replica set called rs1. The members of replica set rs1 are on the following hosts:

  • mongodb3.example.net

  • mongodb4.example.net

  • mongodb5.example.net

1

For each mongod instance in the replica set, create a configuration file with these options:

Option
Value
The path to the key file used for your initial replica set.
rs1
shardsvr
localhost, followed by any other hostnames on which the mongod should listen for client connections.
security:
keyFile: <PATH_TO_KEYFILE>
replication:
replSetName: rs1
sharding:
clusterRole: shardsvr
net:
bindIp: localhost,<hostname(s)>

Include additional options as appropriate for your deployment.

For each member, start a mongod with the following options:

Option
Value
rs1
shardsvr
x509
requireTLS
The absolute path to the .pem file that contains both the TLS certificate and key.
The absolute path to the .pem file that contains the root certificate chain from the Certificate Authority.
localhost, followed by any other hostnames on which the mongod should listen for client connections.
replication:
replSetName: rs1
sharding:
clusterRole: shardsvr
security:
clusterAuthMode: x509
net:
tls:
mode: requireTLS
certificateKeyFile: <FILE_WITH_COMBINED_CERT_AND_KEY>
CAFile: <CA_FILE>
bindIp: localhost,<hostname(s)>

Deploy the mongod with your specified configuration:

mongod --config <PATH_TO_CONFIG_FILE>

Note

When you specify the --shardsvr option for a mongod instance, the instance runs on port 27018 by default.

2
3

Use mongosh to connect to one of the replica set members. For example:

mongosh "mongodb://mongodb3.example.net:27018"
mongosh "mongodb://mongodb3.example.net:27018" --tls --tlsCAFile <CA_FILE> --tlsCertificateKeyFile <filename>
4

In mongosh, run the rs.initiate() method to initiate a replica set that contains the current member:

rs.initiate( {
_id : "rs1",
members: [
{ _id: 0, host: "mongodb3.example.net:27018" },
{ _id: 1, host: "mongodb4.example.net:27018" },
{ _id: 2, host: "mongodb5.example.net:27018" }
]
} )

The preceding command requires the localhost exception to perform administrative actions without authentication.

Important

Run rs.initiate() on just one and only one mongod instance for the replica set.

5

After you deploy the replica set, use the localhost exception to create the replica set's first user.

1

To determine the primary, run rs.status():

rs.status()

In the command output, the replSetGetStatus.members[n].stateStr field indicates which member is the primary.

2

Connect to the replica set primary with mongosh. For example, if the primary is mongodb4.example.net, run this command:

mongosh "mongodb://mongodb4.example.net:27018"
mongosh "mongodb://mongodb4.example.net:27018" --tls --tlsCAFile <CA_FILE> --tlsCertificateKeyFile <filename>
3

Run the following db.createUser() method to create a user named rs1Admin with the userAdmin role:

use admin
db.createUser(
{
user: "rs1Admin",
pwd: passwordPrompt(),
roles: [
{ role: "userAdmin", db: "admin" }
]
}
)

After you run the command, the database prompts you to enter a password for the rs1Admin user.

Add the new replica set, rs1, to the sharded cluster.

1

Run the following command from the command line to connect to the mongos instance running on host mongodb6.example.net:

mongosh "mongodb://admin01@mongodb6.example.net:27017/admin"
mongosh "mongodb://admin01@mongodb6.example.net:27017/admin" --tls --tlsCAFile <CA_FILE> --tlsCertificateKeyFile <filename>

This command authenticates you as the admin01 user you created on the sharded cluster. After you enter the command, enter your user's password.

2

After you connect to the mongos, add the replica set rs1 as a shard to the cluster with the sh.addShard() method:

sh.addShard( "rs1/mongodb3.example.net:27018,mongodb4.example.net:27018,mongodb5.example.net:27018" )

The final step of the procedure is to shard a collection in the sharded cluster.

1

Determine the shard key for the collection. The shard key indicates how MongoDB distributes the documents between shards. Good shard keys:

  • Have values that are evenly distributed among all documents.

  • Group documents that are often accessed at the same time into contiguous chunks.

  • Allow for effective distribution of activity among shards.

For more information, see Choose a Shard Key.

This procedure uses the number field as the shard key for the test_collection collection.

2

Before you shard a non-empty collection, create an index on the shard key:

use test
db.test_collection.createIndex( { "number" : 1 } )
3

In the test database, shard the test_collection. Specify number as the shard key.

sh.shardCollection( "test.test_collection", { "number" : 1 } )

The next time that the balancer runs, it redistributes chunks of documents between shards. As clients insert additional documents into this collection, the mongos routes the documents to the appropriate shard.

Tip

Schedule the balancing window

When the balancer redistributes chunks, it may negatively impact your application's performance. To minimize performance impact, you can specify when the balancer runs so it does not run during peak hours. To learn more, see Schedule the Balancing Window.

For more sharding tutorials and procedures, see these pages:

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Drop a Hashed Shard Key Index