result of a count() on a query that returns nothing should be 0 ?

[zerthimon]

What did you do?
count(container_last_seen{name="container_that_doesn't_exist"})

What did you expect to see?
0

What did you see instead? Under which circumstances?
"no data"

[brian-brazil]

This is correct. You're probably looking for the absent function.

[zerthimon]

@brian-brazil I'm trying to make prometheus to alert when count of the containers that match a specific pattern in a geo region drops below some number:

IF count(container_last_seen{environment="prod",name=~"notification_sender.*",roles=~".*application-server.*"}) by (geo_region) < 4

So this works until there are no containers of this name in the region ... then the value becomes "no data" and that's not < 4 ... so there is no alert ...

I cant see how absent() may help me here...

[juliusv]

Yeah, absent() is probably the way to go. There's also count_scalar(), which outputs 0 for an empty input vector, but that outputs a scalar without any dimensional information.

…

On Thu, Dec 15, 2016 at 6:24 PM, Lior Goikhburg ***@***.***> wrote: @brian-brazil <https://github.com/brian-brazil> I'm trying to make prometheus to alert when count of the containers that match a specific pattern in a geo region drops below some number: IF count(container_last_seen{environment="prod",name=~"notification_sender.*",roles=~".*application-server.*"}) by (geo_region) < 4 So this works until there is no containers of this name in the region ... then the value becomes "no data" and that's not < 4 ... so there is no alert ... I can see how absent() may help me here... — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#2286 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAg1mPXncyVis81Rx1mIWiXRDe0E1Dpcks5rIXe6gaJpZM4LOTeb> .

[zerthimon]

@juliusv yeah, I tried count_scalar() but I can't use aggregation with it. As for absent() ... I'm still out of ideas here.

How would you address this use case:

1. an EC2 regions with application servers running docker containers.
2. Cadvisors on every server provide container names.
3. The containers are named with a specific pattern:

• notification_checker[0-9]
• notification_sender[0-9]

4. I need an alert when the number of container of the same pattern (eg. notification_sender-.*) in region drops below 4.
5. alert also has to fire if there are no (0) containers that match the pattern in region.

The best query I could come up with is this:

count(container_last_seen{environment="prod",name=~"notification_sender.*",roles=~".*application-server.*"}) by (geo_region) < 4

The result of the query is:

{geo_region="tokyo"}	4
{geo_region="sydney"}	4
{geo_region="singapore"}	4
{geo_region="saopaulo"}	4
{geo_region="virginia"}	4
{geo_region="dublin"}	4

Which is great... but... It can't get me a region where there are no containers (0), cause for some reason count() doesn't work for 0 elements in vector ...
I'd expect to have also:

{geo_region="california"}   0

[grobie]

Please use the prometheus-users mailing list for questions.

[fortman]

@zerthimon You might want to use 'bool' with your comparator
count(container_last_seen{environment="prod",name="notification_sender.*",roles=".application-server."}) by (geo_region) < bool 4
or something like that. Play with bool
Also the link to the mailing list doesn't work for me.

[baifeg]

@zerthimon The following expr works for me
count(ALERTS) or (1-absent(ALERTS))

[lilred]

Alternatively, count(ALERTS) or vector(0)