On 8/20/25 18:08, Maxim Dounin wrote:
On Wed, Aug 20, 2025 at 01:06:33PM +0200, Eirik Øverby via nginx wrote:
In the commercial F5 nginx, there has for some time been ways to
monitor the status/usage of shared memory zones and (presumably)
some other run-time stats that remain opaque to users of the
community version. I'm wondering if there are any such
facilities in freenginx - implemented or planned? It would be
nice if the VTS plugin could emit some statistics, for example.
We would be quite interested in such a feature, but realise it
will be a fair amount of work for a relatively narrow audience.
Is there any way we can "encourage" such functionality to be
added, e.g. through financial support or some other means? We
might even be able to produce code to do it, but would prefer if
it was done by someone who is already familiar with (free)nginx
and its architecture - we have no such people on-hand.
Providing better status information might indeed be an interesting
area for improvements.
Right now, the only status information provided by freenginx is
that shown by stub_status, which is quite limited and basically
only shows connections in various states and total
accepts/requests counters. Everything else needs to be monitored
either via logs or with 3rd party modules, like VTS you've
mentioned.
It would be great if you could share which stats you use/monitor,
and how. In particular, it would be interesting to know preferred
data formats.
We use the VTS extension to monitor a number of things, including connection
counts, latencies, etc. We use Prometheus for this, so the data is collected by
the extension and then scraped by Prometheus at regular intervals. The VTS
extensions emits a lot of information, we are not even close to making use of
all of it, but collecting it allows us to drill into the data e.g. after an
incident or when trying to understand application behaviour.
Simplified example config we use:
--
vhost_traffic_status_zone;
vhost_traffic_status_histogram_buckets 0.005 0.01 0.05 0.1 0.2 0.5 1 5 10;
...
location ~ ^/foo/(.*)/bar {
set $loc $1;
# Get stats for individual locations and server ports
vhost_traffic_status_filter_by_set_key $server_port $loc:$request_method;
....
}
location /status {
vhost_traffic_status_display;
}
--
We are currently not using the nginx-internal status endpoint, as I believe VTS
gives us everything it provides - but if the shared memory zone info would be
available there, we'd of course start using it. :)
It would also be interesting to know how you expect to use
information about shared memory zones usage.
I'm mostly concerned about the (apparent?) total lack of information available to guide
sizing of shared memory zones. For rate limiting based purely on source IP it's
"easy" to calculate a worst-case scenario, but in our case we do rate limiting
on a number of different keys - like an md5 of the request string (hard lesson learned
there..), combinations of IP and other request properties, etc.
As for what might be interesting to know, off the top of my head:
- information about utilization (%/bytes) vs max size
- information about number of entries
- if possible the age distribution of entries (to know if entries likely to be
evicted next could be too young, therefore suggesting a larger zone is needed)
- something to see/predict possible fragmentation problems (not sure exactly
what that would be, but knowing what the max size of a new element is at any
given time might be an indicator. If it's low, it might be a problem; if it
fluctuates a lot, that might be a different problem..)
As for improving the VTS module, I don't think it's specific to
freenginx. Information about shared memory zone usage is in the
ngx_slab_pool_t structure since nginx 1.11.7, and it's more or
less a question of showing this information properly. Just in
case, relevant commits are:
changeset: 6828:99770a5ea14f
user: Ruslan Ermilov <r...@nginx.com>
date: Wed Dec 07 22:25:37 2016 +0300
summary: Slab: slots statistics.
changeset: 6829:6e757036e588
user: Ruslan Ermilov <r...@nginx.com>
date: Wed Dec 07 22:25:37 2016 +0300
summary: Slab: free pages statistics.
https://freenginx.org/hg/nginx/rev/99770a5ea14f
https://freenginx.org/hg/nginx/rev/6e757036e588
Are you saying I should speak to the VTS author/project? I can try that of
course, but it would be good to know what data is available first, so I don't
send anyone (else) on a wild goose chase :)
Thanks,
/Eirik
