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• Restore a Sharded Cluster from a Backup

Restore a Sharded Cluster from a Backup

Overview

You can restore a sharded cluster onto new hardware from the artifacts captured by Backup.

You can restore from a snapshot or checkpoint. You must enable checkpoints to use them. When you restore from a checkpoint, Ops Manager takes the snapshot previous to the checkpoint and applies the oplog to create a custom snapshot. Checkpoint recovery takes longer than recovery from a stored snapshot.

Ops Manager provides restore files as downloadable archives. You receive a separate .tar.gz file for each shard and one .tar.gz file for the config servers.

Sequence

The sequence to restore a snapshot is to:

• select and download the restore files,
• distribute the restore files to their new locations,
• start the mongod instances,
• configure each shard’s replica set, and
• configure and start the cluster.

Considerations

Client Requests During Restoration

You must ensure that the MongoDB deployment does not receive client requests during restoration. You must either:

• restore to new systems with new hostnames and reconfigure your application code once the new deployment is running, or
• ensure that the MongoDB deployment will not receive client requests while you restore data.

Snapshots when Agent Cannot Stop Balancer

Ops Manager displays a warning next to cluster snapshots taken while the balancer is enabled. If you restore from such a snapshot, you run the risk of lost or orphaned data. For more information, see Snapshots when Agent Cannot Stop Balancer.

Procedures

Select and Download the Snapshot Files

1

Select the Backup tab and then Overview page.

2

On the line listing the process, click the ellipsis icon and select Restore.

3

Select the restore point.

Select the restore point, enter information as needed, and then click Next:

Snapshot	Restores from a scheduled snapshot. Select the snapshot from which to restore.
Point In Time	Creates a custom snapshot based on a checkpoint. Select a Date and Time and click Next.

4

Select how to receive the restore files.

Select the restore method, format, and destination. Enter information as needed, and then click Finalize Request:

Pull Via Secure HTTP	Create a one-time direct download link. If you select this, click Finalize Request and skip the rest of this procedure.
Push Via Secure Copy	Direct Ops Manager to copy the restore files to your server via SCP. To use this option you must have an existing key pair that Ops Manager can use to transmit the files. See Generate a Key Pair for SCP Restores. Windows machines do not come with SCP and require additional setup outside the scope of this manual.
Format	Sets the format of the restore files: Individual DB Files: Transmits MongoDB data files produced by Ops Manager Backup directly to the target directory. The data is compressed during transmission. Archive (tar.gz): Delivers database files in a single tar.gz file that you must extract before reconstructing databases. With Archive (tar.gz) delivery, you need sufficient space on the destination server for the archive and the extracted files.
SCP Host	The hostname of the server to receive the files.
SCP Port	The port of the server to receive the files.
SCP User	The username used to access to the server.
Auth Method	Select whether to use a username and password or an SSH certificate to authenticate to the server.
Password	The user password used to access to the server.
Passphrase	The SSH passphrase used to access to the server.
Target Directory	The absolute path to the directory on the server to which to copy the restore files.

5

Retrieve the snapshot.

If you selected Pull Via Secure HTTP, Ops Manager creates links to the snapshot that by default are available for an hour and can be used just once. To download the snapshot files, select the Backup tab and then Restore History page. When the restore job completes, a download link appears for each shard and for one of the config servers. Click each link to download the files and copy each to its server. For a shard, copy the file to every member of the shard’s replica set.

If you selected Push Via Secure Copy, Ops Manager copies the files to the server directory you specfied. To verify that the files are complete, see the section on how to validate an SCP restore. For each shard, copy its restore file to every member of the shard’s replica set.

Restore Each Shard’s Primary

For all shards, restore the primary. You must have a copy of the snapshot on the server that provides the primary:

1

Shut down the entire replica set.

Shut down the replica set’s mongod processes using one of the following methods, depending on your configuration:

• Automated Deployment:

  If you use Ops Manager Automation to manage the replica set, you must shut down through the Ops Manager console. See Shut Down a MongoDB Process.

• Non-Automated Deployment on MongoDB 2.6 or Later:

  Connect to each member of the set and issue the following:

  copy

  use admin
  db.shutdownServer()
  

• Non-Automated Deployment on MongoDB 2.4 or earlier:

  Connect to each member of the set and issue the following:

  copy

  use admin
  db.shutdownServer( { force: true } )
  

2

Restore the snapshot data files to the primary.

Extract the data files to the location where the mongod instance will access them through the dbpath setting. If you are restoring to existing hardware, use a different data directory than used previously. The following are example commands:

copy

tar -xvf <backup-restore-name>.tar.gz
mv <backup-restore-name> /data

3

Start the primary with the new dbpath.

For example:

copy

mongod --dbpath /<path-to-data> --replSet <replica-set-name> --logpath /<path-to-data>/mongodb.log --fork

4

Connect to the primary and initiate the replica set.

For example, first issue the following to connect:

copy

mongo

And then issue rs.initiate():

copy

rs.initiate()

5

Restart the primary as a standalone, without the --replSet option.

Use the following sequence:

1. Shut down the process using one of the following methods:

   • Automated Deployment:

     Shut down through the Ops Manager console. See Shut Down a MongoDB Process.

   • Non-Automated Deployment on MongoDB 2.6 or Later:

     copy

     use admin
     db.shutdownServer()
     

   • Non-Automated Deployment on MongoDB 2.4 or earlier:

     copy

     use admin
     db.shutdownServer( { force: true } )
     

2. Restart the process as a standalone:

   copy

   mongod --dbpath /<path-to-data> --logpath /<path-to-data>/mongodb.log --fork
   

6

Connect to the primary and drop the oplog.

For example, first issue the following to connect:

copy

mongo

And then issue rs.drop() to drop the oplog.

copy

use local
db.oplog.rs.drop()

7

Run the seedSecondary.sh script on the primary.

The seedSecondary.sh script re-creates the oplog collection and seeds it with the timestamp of the snapshot’s creation. This will allow the secondary to come back up to time without requiring a full initial sync. This script is customized by Ops Manager for this particular snapshot and is included in the backup restore file.

Use the appropriate script for your operating system:

UNIX-based	seedSecondary.sh
Windows	seedSecondary.bat

This script recreates the oplog collection and seeds it with the timestamp of the snapshot’s creation. This allows the secondary to come back up to time without requiring a full initial sync. Ops Manager customizes this script for this particular snapshot and is included in the backup restore file.

To run the script, issue the following command, where:

<mongodPort>	The port of the mongod process
<oplogSizeInGigabytes>	The size of the replica set’s oplog
<replicaSetName>	The name of the replica set
<primaryHost:primaryPort>	The hostname:port combination for the replica set’s primary

• For UNIX-based systems:

  copy

  ./seedSecondary.sh <mongodPort> <oplogSizeInGigabytes> <replicaSetName> <primaryHost:primaryPort>
  ./seedSecondary.sh 27018 2 rs-1 primaryHost.example.com:27017
  

• For Windows-based systems:

  copy

  .\seedSecondary.bat <mongodPort> <oplogSizeInGigabytes> <replicaSetName> <primaryHost:primaryPort>
  .\seedSecondary.bat 27018 2 rs-1 primaryHost.example.com:27017
  

8

Restart the primary as part of a replica set.

Use the following sequence:

1. Shut down the process using one of the following methods:

   • Automated Deployment:

     Shut down through the Ops Manager console. See Shut Down a MongoDB Process.

   • Non-Automated Deployment on MongoDB 2.6 or Later:

     copy

     use admin
     db.shutdownServer()
     

   • Non-Automated Deployment on MongoDB 2.4 or earlier:

     copy

     use admin
     db.shutdownServer( { force: true } )
     

2. Restart the process as part of a replica set:

   copy

   mongod --dbpath /<path-to-data> --replSet <replica-set-name>
   

Restore All Secondaries

After you have restored the primary for a shard you can restore all secondaries. You must have a copy of the snapshot on all servers that provide the secondaries:

1

Connect to the server where you will create the new secondary.

2

Restore the snapshot data files to the secondary.

Extract the data files to the location where the mongod instance will access them through the dbpath setting. If you are restoring to existing hardware, use a different data directory than used previously. The following are example commands:

copy

tar -xvf <backup-restore-name>.tar.gz
mv <backup-restore-name> /data

3

Start the secondary as a standalone, without the --replSet option.

Use the following sequence:

1. Shut down the process using one of the following methods:

   • Automated Deployment:

     Shut down through the Ops Manager console. See Shut Down a MongoDB Process.

   • Non-Automated Deployment on MongoDB 2.6 or Later:

     copy

     use admin
     db.shutdownServer()
     

   • Non-Automated Deployment on MongoDB 2.4 or earlier:

     copy

     use admin
     db.shutdownServer( { force: true } )
     

2. Restart the process as a standalone:

   copy

   mongod --dbpath /<path-to-data> --logpath /<path-to-data>/mongodb.log --fork
   

4

Run the seedSecondary.sh script on the secondary.

The seedSecondary.sh script re-creates the oplog collection and seeds it with the timestamp of the snapshot’s creation. This will allow the secondary to come back up to time without requiring a full initial sync. This script is customized by Ops Manager for this particular snapshot and is included in the backup restore file.

Use the appropriate script for your operating system:

UNIX-based	seedSecondary.sh
Windows	seedSecondary.bat

This script recreates the oplog collection and seeds it with the timestamp of the snapshot’s creation. This allows the secondary to come back up to time without requiring a full initial sync. Ops Manager customizes this script for this particular snapshot and is included in the backup restore file.

To run the script, issue the following command, where:

<mongodPort>	The port of the mongod process
<oplogSizeInGigabytes>	The size of the replica set’s oplog
<replicaSetName>	The name of the replica set
<primaryHost:primaryPort>	The hostname:port combination for the replica set’s primary

• For UNIX-based systems:

  copy

  ./seedSecondary.sh <mongodPort> <oplogSizeInGigabytes> <replicaSetName> <primaryHost:primaryPort>
  ./seedSecondary.sh 27018 2 rs-1 primaryHost.example.com:27017
  

• For Windows-based systems:

  copy

  .\seedSecondary.bat <mongodPort> <oplogSizeInGigabytes> <replicaSetName> <primaryHost:primaryPort>
  .\seedSecondary.bat 27018 2 rs-1 primaryHost.example.com:27017
  

5

Restart the secondary as part of the replica set.

Use the following sequence:

1. Shut down the process using one of the following methods:

   • Automated Deployment:

     Shut down through the Ops Manager console. See Shut Down a MongoDB Process.

   • Non-Automated Deployment on MongoDB 2.6 or Later:

     copy

     use admin
     db.shutdownServer()
     

   • Non-Automated Deployment on MongoDB 2.4 or earlier:

     copy

     use admin
     db.shutdownServer( { force: true } )
     

2. Restart the process as part of a replica set:

   copy

   mongod --dbpath /<path-to-data> --replSet <replica-set-name>
   

6

Connect to the primary and add the secondary to the replica set.

Connect to the primary and use rs.add() to add the secondary to the replica set.

copy

rs.add("<host>:<port>")

Repeat this operation for each member of the set.

Restore Each Config Server

Perform this procedure separately for each config server. Each config server must have a copy of the tar file with the config server data.

1

Restore the snapshot to the config server.

Extract the data files to the location where the config server’s mongod instance will access them. This is the location you will specify as the storage.dbPath when running mongod for the config server.

copy

tar -xvf <backup-restore-name>.tar.gz
mv <backup-restore-name> /data

2

Start the config server.

The following example starts the config server using the new data:

copy

mongod --configsvr --dbpath /data

3

Update the sharded cluster metadata.

If the new shards do not have the same hostnames and ports as the original cluster, you must update the shard metadata. To do this, connect to each config server and update the data.

First connect to the config server with the mongo shell. For example:

copy

mongo

Then access the shards collection in the config database. For example:

copy

use config
db.shards.find().pretty()

The find() method returns the documents in the shards collection. The collection contains a document for each shard in the cluster. The host field for a shard displays the name of the shard’s replica set and then the hostname and port of the shard. For example:

copy

{ "_id" : "shard0000", "host" : "shard1/localhost:30000" }

To change a shard’s hostname and port, use the MongoDB update() command to modify the documents in the shards collection.

Start the mongos

Start the cluster’s mongos bound to your new config servers.

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