[libvirt] [PATCHv2] Do not keep empty log files for deleted domains

[Daniel P. Berrangé]

On Tue, Jul 09, 2019 at 03:51:41AM +0200, Jan Zerebecki wrote:
> 
> 
> On 08/07/2019 23.28, Jim Fehlig wrote:
> > On 7/8/19 12:28 PM, Jan Zerebecki wrote:
> >> With logrotates copytruncate when e.g. domain1 doesn't exist anymore
> >> /var/log/libvirt/qemu/domain1.log will still exist after rotation even
> >> though it will never be written to. When new domain names keep getting
> >> used this leads to a lot of empty logfiles. This may lead to slowdown or
> >> lack of free disk space / inodes.
> >>
> >> Fix this by replacing copytruncate with the apropriate postrotate
> >> command to reopen log files. Thus after the apropriate time log files
> >> for deleted domains will be gone. This also has the advantage that the
> >> chance for loss of a few lines during copytruncate is gone.
> >>
> >> This only fixes the issue for qemu domains, others still have the same
> >> problem unfixed.
> >>
> >> Signed-off-by: Jan Zerebecki <jan.suse at zerebecki.de>
> >> ---
> >> v2: drop changes to other logrotate confis
> >>
> >>   src/remote/libvirtd.qemu.logrotate.in | 4 +++-
> >>   1 file changed, 3 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/src/remote/libvirtd.qemu.logrotate.in b/src/remote/libvirtd.qemu.logrotate.in
> >> index cdb399ef23..95407cec1a 100644
> >> --- a/src/remote/libvirtd.qemu.logrotate.in
> >> +++ b/src/remote/libvirtd.qemu.logrotate.in
> >> @@ -4,5 +4,7 @@
> >>           rotate 4
> >>           compress
> >>           delaycompress
> >> -        copytruncate
> >> +        postrotate
> >> +                /usr/bin/killall -USR1 virtlogd
> >> +        endscript
> >>   }
> > 
> > In V1 Daniel said "logrotate should not be in effect when virtlogd is running".
> As suggested the logrotate config does those things which virtlogd
> doesn't, so they fit well together.
> 
> On 03/07/2019 10.42, Daniel P. Berrangé wrote:
> > We should
> > ensure that logrotate rollover size is *larger* than the rollover size
> > configured for virtlogd.
> 
> This is the case.
> 
> That someone has virtlogd running does not necessarily mean they don't
> want logrotate to run. virtlogd does not support rotating out logs for
> domains that don't exist anymore, which is the problem this patch
> intends to fix with logrotate. Any suggestion for an alternate
> implementation should at least consider how to fix the problem
> mentioned. It also does not support rotating by time which some might
> want to use to minimize their data retention.

If virtlogd is active, we do *not* want logrotate doing anything at all.
Trying to get sensible interaction between two separate log rotation
apps is adding too much complexity.


Further, any purging of log files needs to take in to account what
guests actually exist in libvirt. The proposed change has no such
checks. It must only purge log files for guests which are neither
running, nor have any persistent config on disk, and where the log
file is older than "N days" for some configurable "N".

Regards,
Daniel
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