[syslog-ng]Reliable syslog and network outages

[Amodiovalerio Verde]

Syslog-ng keep the undelievarable messages in internal queue ( memory )

(Naturally when you reboot your syslog-ng machine you lost all the queue)

As far as there is some space in the queue...messages aren't lost and sended
as soon as the receiver came back.

When the queue is filled new messages will be lost.

I've done extensive testing with syslog-ng, some own parsing engine and
my-sql.

I can assure that syslog-ng handles load of thousands of message for second
( i tried up to 15000 ), and the queue works
really good when you've some program destinations that are slower than a
burst of messages.

Also if you have more destinations, syslog-ng doesn't wait for all the
destinations became available to empty its queue,
but keep in the queue only the messages for the unreachable destinations.

That's works fine when you have some external parser that stores messages in
a db.

When the connection to the db is broken, parsers bloks on connection and
doesn't read their stdin.

That way syslog-ng queue the messages and it feeds them when the connection
to the db is available again.


Amodiovalerio Verde
Security Project Manager


----- Original Message -----
From: "Roland Turner" <raz.flfybt.at@countersnipe.com>
To: <syslog-ng@lists.balabit.hu>
Sent: Friday, August 15, 2003 6:27 PM
Subject: [syslog-ng]Reliable syslog and network outages


> I'm trying to work out whether syslog-ng can deliver syslog messages
> reliably in the face of client reboots during network partitions.
>
>  From reading the documentation, it is not clear where log_fifo stores
> its data (disk or memory) and therefore whether or not log entries on a
> remote syslog client that queue up during a partition of the network
> which seperates syslog client from loghost will remain queued if the
> syslog client host reboots. If my approach is unworkable, pointers or
> aid on how to solve the general problem another way would be greatly
> appreciated.
>
> Here are the details:
>
> 1. Several administered machines are located at diverse locations,
> generally where they are used primarily/entirely by local users.
>
> 2. Local users can ordinarily continue to do useful work even if they
> lose external network connectivity for a while; consequently HA network
> connectivity is not a user requirement.
>
> 3. The machines do not generally require direct intervention very often,
> so from an administration standpoint, 100% reachability is also not a
> requirement.
>
> 4. As a result of points 2 and 3, highly reliable connectivity is not
> available; outages of minutes or hours really do occur.
>
> 5. Pre-syslog-ng implementations of syslog using UDP will simply lose
> all log entries during the time that a network is partitioned. This is
> definitely not OK.
>
> 6. Syslog-ng appears to offer TCP-based delivery which certainly solves
> one issue; normal network paket loss is not an issue.
>
> 7. Syslog-ng appears to maintain an internal FIFO which, if sized large
> enough on a syslog relay host at the remote location(s), could collect
> all log information generated during a partition and then successfully
> deliver it when connectivity is restored.
>
> 8. If, however, syslog-ng's internal FIFO is memory-based then if the
> remote location's syslog relay host is rebooted during the network
> partition then all that it has accumulated and not yet transferred will
> be lost. (Similarly if the death of the TCP connection is treated as
> reason to give up, rather than continually retry.)
>
> 9. What information I have found on dealing with this appears to deal
> with loghost unreliability rather than network unreliability, and thus
> recommends providing HA through additional, redundant, loghosts. Setting
>   aside the problems in reconcilliation of logs that this implies, it
> takes away the reason for having syslog deliver via IP directly (rather
> than, say, email) entirely.
>
> Does syslog-ng provide a means to deal with this problem? Does some
> other solution exist?
>
> Thanks in advance.
>
> - Raz
>
>
>
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