Getting a count of distinct label values in prometheus/grafana

Question

I am trying to create a table/chart in Grafana showing the total number of unique users who have logged in to a given application over a given time range (e.g. last 24 hours). I have a metric, app_request_path which records the number of requests hitting a specific path per minute:

app_request_count{app="my-app", path="/login"}

This gives me the following:

    app_request_count{app="my-app",path="/login",status="200",username="username1"}
    app_request_count{app="my-app",path="/login",status="200",username="username2"}

Now I want to count the number of unique usernames, so I run:

count_values("username", app_request_count{app="my_app", path="/login"})

and I get:

    {username="0"}
    {username="1"}
    {username="2"}
    {username="3"}
    {username="4"}
    {username="5"}

What am I missing / what am I doing wrong? Ideally I'd like to get a single scalar value that display the total number of unique usernames who have logged in in the past 24 hours.

Many thanks.

Answer 1

count without (username)(app_request_count)

count_values is for metric values, count is for time series. It's also not advised to have something like usernames as label values as they tend to be high cardinality. They may also be PII, which could have legal implications.