HDFS Transparent Data Encryption At-Rest was introduced in Hadoop 2.6 to allow create encryption zone on top of a single HDFS directory. Files under the root directory of the encryption zone will be encrypted/decrypted transparently upon HDFS client write or read operations.
Generally, it does not support rename(without data copying) across encryption zones or between encryption zone and non-encryption zone because different security settings of encryption zones. However, there are certain use cases where efficient rename support is desired. This JIRA is to propose better support of two such use cases “Scratch Space” (a.k.a. staging area) and “Soft Delete” (a.k.a. trash) with HDFS encryption zones.
“Scratch Space” is widely used in Hadoop jobs, which requires efficient rename support. Temporary files from MR jobs are usually stored in staging area outside encryption zone such as “/tmp” directory and then rename to targeted directories as specified once the data is ready to be further processed.
Below is a summary of supported/unsupported cases from latest Hadoop:
- Rename within the encryption zone is supported
- Rename the entire encryption zone by moving the root directory of the zone is allowed.
- Rename sub-directory/file from encryption zone to non-encryption zone is not allowed.
- Rename sub-directory/file from encryption zone A to encryption zone B is not allowed.
- Rename from non-encryption zone to encryption zone is not allowed.
“Soft delete” (a.k.a. trash) is a client-side “soft delete” feature that helps prevent accidental deletion of files and directories. If trash is enabled and a file or directory is deleted using the Hadoop shell, the file is moved to the .Trash directory of the user's home directory instead of being deleted. Deleted files are initially moved (renamed) to the Current sub-directory of the .Trash directory with original path being preserved. Files and directories in the trash can be restored simply by moving them to a location outside the .Trash directory.
Due to the limited rename support, delete sub-directory/file within encryption zone with trash feature is not allowed. Client has to use -skipTrash option to work around this.
HADOOP-10902 and HDFS-6767 improved the error message but without a complete solution to the problem.
We propose to solve the problem by generalizing the mapping between encryption zone and its underlying HDFS directories from 1:1 today to 1:N. The encryption zone should allow non-overlapped directories such as scratch space or soft delete "trash" locations to be added/removed dynamically after creation. This way, rename for "scratch space" and "soft delete" can be better supported without breaking the assumption that rename is only supported "within the zone".