How to make juju aware of IP address changes?

Peter Waller peter at
Fri Dec 6 09:52:33 UTC 2013

On 5 December 2013 18:52, Mark Shuttleworth <mark at> wrote:

> Would it help if Juju could maintain an awareness of the disk situation
> and gracefully avoid making the problem worse (and avoid corruption) by
> going read-only when disk is low?

Out of disk is quite an insidious position to be in. I'd say it is first
important not to cause it, and then not to get corrupted if it does happen.

There were two things that caused it. The first was that all of the
machines were sending logging information to all-machines.log and they were
all doing something every second or so and failing, which lead to a rapid
log build up. Given that logging information is useful, I don't see any
option to silence it before running out of disk because it might make it
impossible to diagnose a problem. The core issue was probably that all of
the agents were rapidly retrying something and all failing. Some form of
exponential backoff would have helped there.

Once we had suppressed that problem, the mongo database was in a strange
condition which caused it to eat disk space at 75mb/sec. This persisted
even after restarts of juju-db. I don't know if the root cause of this is
understood. It did seem that the resulting files were mostly null bytes,
which is probably telling. We let it eat 14GB on another disk before
stopping it and doing a mongodump/restore back to a ~300mb database, which
fixed the rapid growth but revealed that there was something wrong with the
transactions, presumably because one was incorrectly written owing to out
of disk.

After this Roger encountered many small issues which I presume were
remnants of the age of our environment and our abuse of it because we
didn't understand juju's model (and/or juju has changed in lots of little
ways since the system was created).

That's my brief understanding of the situation.

All the best,

- Peter
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