Grafana Variable based on other variables

Question

I have a Grafana dashboard panel, it does have a variable called host, host can be domain1.com, domain2.com, domain3.com, domain4.com. I need another custom variable (var2) that be somehow connected to the host, for instance when user choose domain1.com var2 become "some text", if host is domain2.com var2 become "another text, etc. How can I define this custom variable?

Answer 1

You have two way of dealing with this:

Easier one

Use single variable with labels.

For example Custom variable can be defined with the following value:

label1 : value1, label2 : value2

This way you will see in dropdown lables (label1, label2).

And you can use this variable in the following way:

• $var will return value of selected item, for example value1,
• ${var:text} will return label of selected item, for example lable1.

You can see demo here.

More agile one

You can use two variables and some (pseudo-)query with first variable as parameter to generate value of the second one.

This way you can chain multiple variables and create complex rules. But it requires a data source, that will allow to evaluate this rules.

Here are couple examples of data sources allowing for such rules:

SQL

With SQL data source one can utilize case statement to decode value.

For example with MySQL data source your query will look something like this:

select case 
  when '$var' = 'host1.com' then 'some text'
  when '$var' = 'host2.com' then 'some other text'
  else 'Unexpected text'
end

Prometheus

In Prometheus such a construction can be created by combination of boolean operators and absent.

For case where initial value numeric:

query_result(
  absent(non_existent{pseudo_label="value1"}) * 1 == $var1 or
  absent(non_existent{pseudo_label="value2"}) * 2 == $var1 or
  absent(non_existent{pseudo_label="value3"}) * 3 == $var1
)

For string values:

query_result(
  (absent(non_existent{pseudo_label="output1"}) and on() (absent(non_existent{pseudo_input="input1"}) and absent(non_existent{pseudo_input="$value1"}))) or
  (absent(non_existent{pseudo_label="output2"}) and on() (absent(non_existent{pseudo_input="input2"}) and absent(non_existent{pseudo_input="$value1"}))) or
  (absent(non_existent{pseudo_label="output3"}) and on() (absent(non_existent{pseudo_input="input3"}) and absent(non_existent{pseudo_input="$value1"})))

In both Prometheus' cases you need to provide Regex for linked variable, to extract label from result of query. For examples provided here regex will be /pseudo_label="(.+?)"/