[Gross] Weighted checks in production

Jesse Thompson jesse.thompson at doit.wisc.edu
Wed Apr 9 20:53:32 EEST 2008

Eino Tuominen wrote:
> Jesse Thompson wrote:
>> Cool!  Nice work, as always.  I will try this out soon, I hope.
> It would be nice to get some feedback how the current version is behaving.
>>> I have now uploaded gross-svn-236.tar.gz, it's running now in 
>>> production here. I couldn't get check_blocker to reuse connections as 
>>> Sophos' blockerd keeps shutting every connection down right after the 
>>> answer. And, now there's watchdog to see if blocker threads get stuck.
>> Was this a bug?  I can't remember the details.
> I don't remember if there has been any discussion about this in perl-mx 
> mailing list. But I even configured a test server to have postfix make 
> policy queries to blockerd, and even then it's one query / connection. 
> Blockerd just closes the connection. I will do some reverse engineering 
> with sendmail. It would be really nice if those connections could be 
> reused.
>> Yeah, I think that this is the most efficient way to enable longer 
>> greylisted states.  From what I understand, the current method of 
>> setting a greylist time period keeps the entry in memory and waits X 
>> seconds before updating the filter.  This seems to me like it wouldn't 
>> scale well to larger time values.
> Yes, the current implementation uses a delayed message queue implemented 
> in msgqueue.c. Message queues are basically linked lists with mutexes, 
> and delay queue is just two message queues (inq and outq) with a handler 
> thread moving messages from inq to outq. It actually scales well 
> performance-wise. The biggest problem with them is that they are saved 
> in memory. Should both replicated grossd nodes fail at the same time, 
> the queue is lost.
> Now that most of the messages will be blocked and only a fraction will 
> be greylisted, it would be possible to use a lot bigger number_buffers 
> with a bit smaller filter_bits and rotate_interval. How about 22 bits, 
> 15 minutes and 48 buffers?
> 13410 grossd      25M   200K-   25M    46M
> New options to implement could be:
> 'skip_buffers' = how many (maximum) buffers to skip
> 'skip_style' = how to do the skipping, 'absolute' means that grossd 
> always puts update on the first buffer, 'weighed' (or something) would 
> place more suspicious triplets in the first buffer, and less suspicious 
> triplets nearer to skip limit, so that the greylisting time would be 
> relative to susp_weight.
> If you set skip_buffers = 16 (around 3 hours), skip_style = weighed
> and block_threshold = 9, grey_threshold = 1, then grossd would calculate 
> the filter to update like this
> s = how many to skip, S = skip_buffers, w = total weight from the 
> checks, b = block_threshold, g = grey_threshold
> s = S * ( w - g ) / ( b - g - 1)
> With the given config this would be
> s = 16 * ( w - 1 ) / ( 9 - 1 - 1) = 16 / 7 * ( w - 1)
> If w = 1, then s = 0, with w = 8, s = 16
> With that, more suspicious hosts would wait more, and less suspicious 
> would have to wait less.
> Thoughts? This is not entirely trivial modification, as it means 
> modifications in the code that has been very stable since early days. 
> The good thing is that this is easy to stresstest if implemented.

I think it's a cool idea.  It might be overkill though.  Would it be 
easier to just start with the 'skip_buffers' option with the absolute 
'skip_style' behavior?


   Jesse Thompson
   Email/IM: jesse.thompson at doit.wisc.edu
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