Github user tgravescs commented on a diff in the pull request:

    https://github.com/apache/spark/pull/4688#discussion_r29286123
  
    --- Diff: docs/security.md ---
    @@ -32,6 +32,8 @@ SSL must be configured on each node and configured for 
each component involved i
     ### YARN mode
     The key-store can be prepared on the client side and then distributed and 
used by the executors as the part of the application. It is possible because 
the user is able to deploy files before the application is started in YARN by 
using `spark.yarn.dist.files` or `spark.yarn.dist.archives` configuration 
settings. The responsibility for encryption of transferring these files is on 
YARN side and has nothing to do with Spark.
     
    +For long-running apps like Spark Streaming apps to be able to write to 
HDFS, it is possible to pass a principal and keytab to `spark-submit` via the 
`--principal` and `--keytab` parameters respectively. The keytab passed in will 
be copied over to the machine running the Application Master via the Hadoop 
Distributed Cache (securely - if YARN is configured with SSL and HDFS 
encryption is enabled). The Kerberos login will be periodically renewed using 
this principal and keytab and the delegation tokens required for HDFS will be 
generated periodically so the application can continue writing to HDFS. Please 
note that the HDFS client configuration file, `hdfs-site.xml` on each executor 
node must have the value of `dfs.namenode.delegation.token.renew-interval` be 
the same as it is on the HDFS Namenode for this functionality.
    +
    --- End diff --
    
    remove the reference to the renew-interval if you remove use of it


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