HDFS Encryption Issues

The following are possible workarounds for issues that may arise when encrypting HDFS directories and files. HDFS encryption is sometimes referred to in the documentation as HDFS Transparent Encryption or as HDFS Data at Rest Encryption.

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KMS server jute buffer exception

Description

You see the following error when the KMS (for example, as a ZooKeeper client) jute buffer size is insufficient to hold all the tokens: 
2017-01-31 21:23:56,416 WARN org.apache.zookeeper.ClientCnxn: Session 0x259f5fb3c1000fb for server example.cloudera.com/10.172.0.1:2181, unexpected error, closing socket connection and attempting reconnect
java.io.IOException: Packet len4196356 is out of range!

Solution

Increase the jute buffer size and restart the KMS. In Cloudera Manager, go to the KMS Configuration page, and in the Additional Java Configuration Options for KMS (kms_java_opts) field, enter -Djute.maxbuffer=<number_of_bytes>. Restart the KMS.

Retrieval of encryption keys fails

Description

You see the following error when trying to list encryption keys 
user1@example-sles-4:~> hadoop key list
Cannot list keys for KeyProvider: KMSClientProvider[https: //example-sles-2.example.com:16000/kms/v1/]: Retrieval of all keys failed.

Solution

Make sure your truststore has been updated with the relevant certificate(s), such as the Key Trustee server certificate.

DistCp between unencrypted and encrypted locations fails

Description

By default, DistCp compares checksums provided by the filesystem to verify that data was successfully copied to the destination. However, when copying between unencrypted and encrypted locations, the filesystem checksums will not match since the underlying block data is different.

Solution

Specify the -skipcrccheck and -update distcp flags to avoid verifying checksums.

(CDH 5.6 and lower) Cannot move encrypted files to trash

Description

In CDH 5.6 and lower, with HDFS encryption enabled, you cannot move encrypted files or directories to the trash directory.

Solution

To remove encrypted files/directories, use the following command with the -skipTrash flag specified to bypass trash. 
rm -r -skipTrash /testdir

NameNode - KMS communication fails after long periods of inactivity

Description

Encrypted files and encryption zones cannot be created if a long period of time (by default, 20 hours) has passed since the last time the KMS and NameNode communicated.

Solution

For lower CDH 5 releases, there are two possible workarounds to this issue :
  • You can increase the KMS authentication token validity period to a very high number. Since the default value is 10 hours, this bug will only be encountered after 20 hours of no communication between the NameNode and the KMS. Add the following property to the kms-site.xmlSafety Valve: 
    <property>
<name>hadoop.kms.authentication.token.validity</name> 
<value>SOME VERY HIGH NUMBER</value> 
</property>
  • You can switch the KMS signature secret provider to the string secret provider by adding the following property to the kms-site.xml Safety Valve: 
    <property>
<name>hadoop.kms.authentication.signature.secret</name> 
<value>SOME VERY SECRET STRING</value> 
</property>

HDFS Trash Behaviour with Transparent Encryption Enabled

The Hadoop trash feature helps prevent accidental deletion of files and directories. When you delete a file in HDFS, the file is not immediately expelled from HDFS. Deleted files are first moved to the /user/<username>/.Trash/Current directory, with their original filesystem path being preserved. After a user-configurable period of time (fs.trash.interval), a process known as trash checkpointing renames the Current directory to the current timestamp, that is, /user/<username>/.Trash/<timestamp>. The checkpointing process also checks the rest of the .Trash directory for any existing timestamp directories and removes them from HDFS permanently. You can restore files and directories in the trash simply by moving them to a location outside the .Trash directory.

Trash Behaviour with HDFS Transparent Encryption Enabled

Starting with CDH 5.7, you can delete files or directories that are part of an HDFS encryption zone. As is evident from the procedure described above, moving and renaming files or directories is an important part of trash handling in HDFS. However, currently HDFS transparent encryption only supports renames within an encryption zone. To accommodate this, HDFS creates a local .Trash directory every time a new encryption zone is created. For example, when you create an encryption zone, enc_zone, HDFS will also create the /enc_zone/.Trash/ subdirectory. Files deleted from enc_zone are moved to /enc_zone/.Trash/<username>/Current/. After the checkpoint, the Current directory is renamed to the current timestamp, /enc_zone/.Trash/<username>/<timestamp>.

If you delete the entire encryption zone, it will be moved to the .Trash directory under the user's home directory, /users/<username>/.Trash/Current/enc_zone. Trash checkpointing will occur only after the entire zone has been moved to /users/<username>/.Trash. However, if the user's home directory is already part of an encryption zone, then attempting to delete an encryption zone will fail because you cannot move or rename directories across encryption zones.