Restore a Solr collection

If you have made backups, you can restore a Solr collection using the solrctl utility.

If you are using a secure (Kerberos-enabled) cluster, specify your jaas.conf file by adding the following parameter to each command:

-jaas /path/to/jaas.conf

If TLS is enabled for the Solr service, specify the truststore and password by using the ZKCLI_JVM_FLAGS environment variable before you begin the procedure:

export ZKCLI_JVM_FLAGS="-Djavax.net.ssl.trustStore=/path/to/truststore \
-Djavax.net.ssl.trustStorePassword=trustStorePassword"

If you are restoring from a backup stored on a remote cluster, copy the backup from the remote cluster to the local cluster. If you are restoring from a local backup, skip this step.
Run the following commands on the cluster to which you want to restore the collection:
```
hdfs dfs -mkdir -p /path/to/restore-staging
hadoop distcp <protocol>://<namenode>:<port>/path/to/backup /path/to/restore-staging
```
For example:
- HDFS protocol:
```
hadoop distcp hdfs://nn01.example.com:8020/path/to/backups/tweets-201803281043 /path/to/restore-staging
```
- WebHDFS protocol:
```
hadoop distcp webhdfs://nn01.example.com:20101/path/to/backups/tweets-201803281043 /path/to/restore-staging
```

Start the restore procedure. Run the following command:

solrctl collection --restore <restoreCollectionName> -l <backupLocation> -b <snapshotName> -i <requestId>

Make sure that you use a unique <requestID> each time you run this command.

For example:

solrctl collection --restore tweets -l /path/to/restore-staging -b tweets-201803281043 -i restore-tweets

Monitor the status of the restore operation. Run the following command periodically:
```
solrctl collection --request-status <requestId>
```
Look for <str name="state"> in the output. For example (emphasis added):
```
solrctl collection --request-status restore-tweets
 <?xml version="1.0" encoding="UTF-8"?> <response> <lst name="responseHeader"> <int name="status"> 0</int> <int name="QTime"> 1</int> </lst> \
<lst name="status"> <str name="state"> completed</str> <str name="msg"> found restore-tweets in completed tasks</str> </lst> </response>
```
The state parameter can be one of the following:
- running: The restore operation is running.
- completed: The restore operation is complete.
- failed: The restore operation failed.
- notfound: The specified <requestID> does not exist.