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https://issues.apache.org/jira/browse/HDFS-3680?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13426944#comment-13426944
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Marcelo Vanzin commented on HDFS-3680:
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Answers inline.
bq. With this approach, should namenode run if for some reason we have removed
all the audit loggers from the list? My answer would be no, given the
importance of audit log.
bq. Does the system need a mechanism to add/remove audit loggers? When a failed
logger is fixed, do we need a way to refresh the audit logger so it is picked
up by the Namenode again?
Being of the opinion that making it a list wasn't really needed to start with
(I can't really see a scenario where you'd have more than one custom logger,
which is what my original patch did), I don't think the NameNode should be
stopped. Removing the audit logger from the list means the audit logger is
buggy, which means that we'd be stopping the NameNode because code outside the
control of the NameNode did something bad, which goes back to previous
discussions about how this can end up being blamed on the HDFS code while it's
not HDFS's fault.
I could, though, always fall back to having the default logger in the list if
it ever becomes empty. That would still not generate any audit logs if the
logging system is not configured for it.
bq. When you have multiple audit loggers, is there a need to keep them in sync
or out of sync audit loggers okay?
Not sure what you mean by "in sync", but my answer here is the same regardless:
there is no need to do anything other than what's already being done. Custom
loggers, once called, do what they want with the data, and it's out of the
NameNode's control at that point.
bq. Alternatively, should we consider a separate daemon that runs off of the
audit log written to disk and updates other syncs instead of doing it inline in
the namenode code?
See my comment on 20/Jul/12 . I think that's overkill and creates more problems
than it solves.
> Allows customized audit logging in HDFS FSNamesystem
> ----------------------------------------------------
>
> Key: HDFS-3680
> URL: https://issues.apache.org/jira/browse/HDFS-3680
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: name-node
> Affects Versions: 2.0.0-alpha
> Reporter: Marcelo Vanzin
> Assignee: Marcelo Vanzin
> Priority: Minor
> Attachments: accesslogger-v1.patch, accesslogger-v2.patch,
> hdfs-3680-v3.patch, hdfs-3680-v4.patch, hdfs-3680-v5.patch
>
>
> Currently, FSNamesystem writes audit logs to a logger; that makes it easy to
> get audit logs in some log file. But it makes it kinda tricky to store audit
> logs in any other way (let's say a database), because it would require the
> code to implement a log appender (and thus know what logging system is
> actually being used underneath the façade), and parse the textual log message
> generated by FSNamesystem.
> I'm attaching a patch that introduces a cleaner interface for this use case.
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