Problem

We need to create an instant vector with a given label set.

An example use case would be supplying a default value in combination with or.

Solution

PromQL’s label_replace function can be used to create arbitrary labels by using the empty string as the target label. Combining this with the use of vector to create an instance vector for a given scalar let’s us create an instance vector with an arbitrary label set by

label_replace(
  ...label_replace(vector(<s>), "<name-1>", "<value-1>", "", "")...,
  "<name-n>", "<value-n>", "", ""
)

where <s> is the scalar value for the initial vector as well as <name-i> and <value-i> are placeholders for the target label names and values to create.

Note: The values <value-i> can use variables.

Example

The following expression

label_replace(label_replace(vector(1), "pod_name", "$pod", "", ""), "namespace", "$namespace", "", "")

will create an instant vector with scalar value 1 and pod name $pod as well as namespace $namespace.