No idea. You haven't said what dashboard software you're using, nor what
queries you're using to build that dashboard.
> I want to add one filter so that I can be able to know which servers are
least used or most used.
Not sure what you mean by a "filter" in this context. A PromQL query using
min() or max() will work over all the values which are present in the
instant vector, which as I said before, is of variable size. It doesn't
have to have a fixed number of inputs.
e.g. given this data
[
node_blah{instance="foo"} 123
node_blah{instance="bar"} 456
node_blah{instance="baz"} 789
]
then
min(node_blah) => 123
On Wednesday, 20 July 2022 at 10:28:58 UTC+1 [email protected] wrote:
> Thanks, Clark and Brian for your reply.
>
> I am using two data sources in my case. i.e Prometheus and Postgres.
>
> In my dashboard, there is a table that contains both Prometheus and
> Postgres data. In this table, there is a column name %cpu used which will
> be obtained from Prometheus.
>
> As Brain said, if the server goes down, we will not get the node level
> metrics and for that particular server, we will have Postgres data but, not
> Prometheus as the server was down.
>
> for example, my dashboard table is as follows:
>
> IP CPU %cpu memory memory_used column1
> column2 column3
> 1.1.1.1 4 0.4% 40gb 60%
> a b c
> 1.1.1.2 8 10% 80gb 30%
> d e f
> 1.1.1.3
> h i j
>
>
> the third server goes down, so we are not able to see the CPU and memory
> values, my question was I want to add one filter so that I can be able to
> know which servers are least used or most used.
>
> The CPU used for the third server will be no data as that server was down.
> can we do any comparison for these servers(servers who went down) so that I
> can filter these servers whose value will be null/no_data.
>
> Thanks & regards,
> Bharath Kumar.
>
> On Wednesday, 20 July 2022 at 14:22:17 UTC+5:30 Brian Candler wrote:
>
>> And just to clarify slightly, there aren't really "null values" in
>> prometheus. A query like "node_blah" returns a *vector* of results, that
>> is, a variable number of values. e.g.
>>
>> [
>> node_blah{instance="foo"} 123
>> node_blah{instance="bar"} 456
>> node_blah{instance="baz"} 789
>> ]
>>
>> If node "baz" goes down, then a query at a later point in time may return
>>
>> [
>> node_blah{instance="foo"} 124
>> node_blah{instance="bar"} 457
>> ]
>>
>> If you want to test for this specific condition, i.e. there is no
>> "node_blah" metric present for a specific instance "baz", then you can form
>> a rather awkward join query using absent() in conjunction with the "up"
>> metric as Stuart described.
>>
>> But usually, you just want to query the "up" metric itself.
>>
>> On Wednesday, 20 July 2022 at 09:38:58 UTC+1 Stuart Clark wrote:
>>
>>> On 20/07/2022 08:49, BHARATH KUMAR wrote:
>>>
>>> Hello all,
>>>
>>> I installed node exporters on many servers (around 300). Few of the
>>> servers are unreachable. So because of that, we are unable to get the CPU,
>>> and memory values of those servers.
>>>
>>> Now I want to add a filter in the Grafana dashboard to check the least
>>> CPU used, most CPU used servers. But due to unreachability, we are not
>>> getting values for a few servers.
>>>
>>> My question is
>>> "*how to compare the output of the Prometheus query is NULL"*
>>>
>>> Generally, I am comparing the output of the prom query like
>>> I) if the CPU usage is less than 10% then I am comparing like
>>> query >=0<=10%
>>> ii) if the CPU usage is greater than 10% and less than 30% then I am
>>> comparing like
>>> query >10<=30
>>> *similarly how to check the null values using the Prometheus query.*
>>>
>>> For servers which can't be scraped there will be no metrics, so any
>>> queries won't have any data to query.
>>>
>>> However Prometheus itself creates certain metrics for all scrape
>>> targets, including one called "up" which is either 0 or 1 - where 0 means
>>> the scrape failed. You can therefore create dashboards and alerts that list
>>> the servers which aren't accessible (up == 0).
>>>
>>> --
>>> Stuart Clark
>>>
>>>
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