Which of the following PromQL queries is invalid?

Themaxoperator in PromQL is anaggregation operator, not abinary vector matching operator. Therefore, the valid syntax for aggregation uses by() or without(), not on().

✅max by (instance) up → Valid; aggregates maximum values per instance.

✅max without (instance) up and max without (instance, job) up → Valid; aggregates over all labels except those listed.

❌max on (instance) (up) → Invalid; the keyword on() is only valid inbinary operations(e.g., +, -, and, or, unless), where two vectors are being matched on specific labels.

Hence, max on (instance) (up) is a syntax error in PromQL because on() cannot be used directly with aggregation operators.