10. Security Support

Spring for Apache Hadoop is aware of the security constraints of the running Hadoop environment and allows its components to be configured as such. For clarity, this document breaks down security into HDFS permissions and user impersonation (also known as secure Hadoop). The rest of this document discusses each component and the impact (and usage) it has on the various SHDP features.

10.1 HDFS permissions

HDFS layer provides file permissions designed to be similar to those present in *nix OS. The official guide explains the major components but in short, the access for each file (whether it's for reading, writing or in case of directories accessing) can be restricted to a certain users or groups. Depending on the user identity (which is typically based on the host operating system), code executing against the Hadoop cluster can see or/and interact with the file-system based on these permissions. Do note that each HDFS or FileSystem implementation can have slightly different semantics or implementation.

SHDP obeys the HDFS permissions, using the identity of the current user (by default) for interacting with the file system. In particular, the HdfsResourceLoader considers when doing pattern matching, only the files that its suppose to see and does not perform any privileged action. It is possible however to specify a different user, meaning the ResourceLoader interacts with HDFS using that user's rights - however this obeys the user impersonation rules. When using different users, it is recommended to create separate ResourceLoader instances (one per user) instead of assigning additional permissions or groups to one user - this makes it easier to manage and wire the different HDFS views without having to modify the ACLs. Note however that when using impersonation, the ResourceLoader might (and will typically) return restricted files that might not be consumed or seen by the callee.

10.2 User impersonation (Kerberos)

Securing a Hadoop cluster can be a difficult task - each machine can have a different set of users and groups, each with different passwords. Hadoop relies on Kerberos, a ticket-based protocol for allowing nodes to communicate over a non-secure network to prove their identity to one another in a secure manner. Unfortunately there is not a lot of documentation on this topic out there however the there are some resources to get you started.

SHDP does not require any extra configuration - it simply obeys the security system in place. By default, when running inside a secure Hadoop, SHDP uses the current user (as expected). It also supports user impersonation, that is, interacting with the Hadoop cluster with a different identity (this allows a superuser to submit job or access hdfs on behalf of another user in a secure way, without leaking permissions). The major MapReduce components, such as job, streaming and tool as well as pig support user impersonation through the user attribute. By default, this property is empty, meaning the current user is used - however one can specify the different identity (also known as ugi) to be used by the target component:

<hdp:job id="jobFromJoe" user="joe" .../>

Note that the user running the application (or the current user) must have the proper kerberos credentials to be able to impersonate the target user (in this case joe).