Restart a Sharded Cluster
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The tutorial is specific to MongoDB 4.4. For earlier versions of MongoDB, refer to the corresponding version of the MongoDB Manual.
This procedure demonstrates the shutdown and startup sequence for restarting a sharded cluster. Stopping or starting the components of a sharded cluster in a different order may cause communication errors between members. For example, shard servers may appear to hang if there are no config servers available.
Important
This procedure should only be performed during a planned maintenance period. During this period, applications should stop all reads and writes to the cluster in order to prevent potential data loss or reading stale data.
Disable the Balancer
Disable the balancer to stop chunk migration and do not perform any metadata write operations until the process finishes. If a migration is in progress, the balancer will complete the in-progress migration before stopping.
To disable the balancer, connect to one of the cluster's
mongos instances and issue the following command: [1]
sh.stopBalancer()
To check the balancer state, issue the sh.getBalancerState()
command.
For more information, see Disable the Balancer.
| [1] | Starting in MongoDB 4.2, sh.stopBalancer() also disables
auto-splitting for the sharded cluster. |
Stop Sharded Cluster
Stop mongos routers.
Run db.shutdownServer() from the admin database on each
mongos router:
use admin db.shutdownServer()
Stop each shard replica set.
Run db.shutdownServer() from the admin database on each
shard replica set member to shutdown
its mongod process. Shutdown all secondary members
before shutting down the primary in each replica set.
Stop config servers.
Run db.shutdownServer() from the admin database on each
of the config servers to
shutdown its mongod process. Shutdown all
secondary members before shutting down the primary.
Start Sharded Cluster
Start config servers.
When starting each mongod, specify the
mongod settings using either a configuration file or the
command line. For more information on startup parameters, see the
mongod reference page.
Configuration File
If using a configuration file, start the mongod with
the --config option set to the configuration file path.
mongod --config <path-to-config-file>
Command Line
If using the command line options, start the mongod
with the --configsvr, --replSet, --bind_ip,
and other options as appropriate to your deployment. For example:
mongod --configsvr --replSet <replica set name> --dbpath <path> --bind_ip localhost,<hostname(s)|ip address(es)>
After starting all config servers, connect to the primary
mongod and run rs.status() to confirm the
health and availability of each CSRS member.
Start each shard replica set.
When starting each mongod, specify the
mongod settings using either a configuration file or the
command line.
Configuration File
If using a configuration file, start the mongod with
the --config option set to the configuration file path.
mongod --config <path-to-config-file>
Command Line
If using the command line option, start the mongod with
the --replSet, --shardsvr, and --bind_ip options,
and other options as appropriate to your deployment. For example:
mongod --shardsvr --replSet <replSetname> --dbpath <path> --bind_ip localhost,<hostname(s)|ip address(es)>
After starting all members of each shard, connect to each primary
mongod and run rs.status() to confirm the health
and availability of each member.
Start mongos routers.
Start mongos routers using either a configuration file or a
command line parameter to specify the config servers.
Configuration File
If using a configuration file, start the mongos specifying
the --config option and the path to the configuration file.
mongos --config <path-to-config>
For more information on the configuration file, see configuration options.
Command Line
If using command line parameters, start the mongos and specify
the --configdb, --bind_ip,
and other options as appropriate to your deployment. For example:
Warning
Before binding to a non-localhost (e.g. publicly accessible) IP address, ensure you have secured your cluster from unauthorized access. For a complete list of security recommendations, see Security Checklist. At minimum, consider enabling authentication and hardening network infrastructure.
mongos --configdb <configReplSetName>/cfg1.example.net:27019,cfg2.example.net:27019 --bind_ip localhost,<hostname(s)|ip address(es)>
Include any other options as appropriate for your deployment.
Re-Enable the Balancer
Re-enable the balancer to resume chunk migrations.
Connect to one of the cluster's mongos instances and run
the sh.startBalancer() command: [2]
sh.startBalancer()
To check the balancer state, issue the sh.getBalancerState()
command.
For more information, see Enable the Balancer.
| [2] | Starting in MongoDB 4.2, sh.startBalancer() also enables
auto-splitting for the sharded cluster. |
Validate Cluster Accessibility
Connect a mongo shell to one of the cluster's
mongos processes. Use sh.status()
to check the overall cluster status.
To confirm that all shards are accessible and communicating, insert
test data into a temporary sharded collection. Confirm that data is
being split and migrated between each shard in your cluster. You can
connect a mongo shell to each shard primary and
use db.collection.find() to validate that the data was
sharded as expected.
Important
To prevent potential data loss or reading stale data, do not start application reads and writes to the cluster until after confirming the cluster is healthy and accessible.