- by default, there is nothing you can make with syslog-ng alone that will not lose data during a network or endpoint outage.

I use rsyslog on clients and relays with TCP disk buffering including relays. Properly measured you should know when you are buffering.

- transporting metadata can tell you which file the data is from, but not where in the file it's from, so you can't really tell if you have duplicate data, or missed data. (The inode number might be handy too)

- behaviour around input file truncation is fuzzy. That a truncation has occured might be useful metadata to send (if you're looking for people fiddling logs).

Any mature log reader should handle those use cases, if you have no control over the rotation is it possible to load the data after rotation? Logrotated has pre and post rotation functions.

- It doesn't seem to be able to encode binary/NULs in the logs, so it cannot relay data from 'untrusted' application logs?
- Not sure what it does with very long lines. Loses data?
Have not seen those cases.

Hope it help a little.

Scot

On Mon, Jan 29, 2018 at 9:34 AM, Declan White <declanw@is.bbc.co.uk> wrote:

Hullo.

I'm trying to fit syslog-ng around a basic problem and looking for tips.

I have log files growing on one machine that I want to follow and reliably replicate to a central machine, so it's effectively a basic 'tail -f' job.
It seems simple, but as I try and close out the possible error conditions it's getting hairier and hairier.

e.g.
- by default, there is nothing you can make with syslog-ng alone that will not lose data during a network or endpoint outage.
- transporting metadata can tell you which file the data is from, but not where in the file it's from, so you can't really tell if you have duplicate data, or missed data. (The inode number might be handy too)
- behaviour around input file truncation is fuzzy. That a truncation has occured might be useful metadata to send (if you're looking for people fiddling logs).
- It doesn't seem to be able to encode binary/NULs in the logs, so it cannot relay data from 'untrusted' application logs?
- Not sure what it does with very long lines. Loses data?

I'm not necessarily looking to get syslog-ng to recreate the file exactly, just to send enough information to allow something else to work out the full order of events.
Googling around to see how others solve this problem, I see people doing infinite rsync loops, or installing large Java beasties, or paying someone else to make it all go away.

I tried using rsyslog, but it melted down into a screaming puddle of nondeterministic threading.

Is what I'm attempting really as hard as it seems?

- D
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