Dashboard variables

[TarasPriadka]

Add support for dashboard variables. Depends on #42

For example here,

df = px.DataFrame(table='http_events', start_time=__time_from)
df['cluster'] = '$clusters'

The $clusters will get replaced with the dashboard variable value.

[nserrino]

Is there a reason we use a different syntax here ($ vs __ prefix) than the time/interval special variables? I would recommend using the same approach for both

[nserrino]

Also, looks like the commit history might be including some other stuff

[TarasPriadka]

Is there a reason we use a different syntax here ($ vs __ prefix) than the time/interval special variables? I would recommend using the same approach for both

This is actually replacing the variables directly in Grafana UI. Previously we handled the __time and other variables ad hoc, but grafana can do it natively from the UI. The benefit of doing that is that you can use any dashboard variable in your scripts, even user defined variables. So we can handle the common case like __start_time, __end_time, but also any other variable such as cluster or pod in the future.

The Grafana UI actually just replaces the $ variables before sending to backend, so we can remove that logic there completely.

Also, looks like the commit history might be including some other stuff

I will rebase on main in a moment.

[nserrino]

So you're saying that the $ replacement is done by Grafana, not manual logic on our side.

In that case, we might want to support $start_time, $interval, and $end_time in addition to __start_time, __interval, and __end_time, so that we can move toward a consistent experience with $ only. I think that would be better than the user having to know both ways, going forward, but we can still support the old way for backwards compatibility

We can therefore update our Grafana plugin to support both and update our example scripts to use $

[TarasPriadka]

So you're saying that the $ replacement is done by Grafana, not manual logic on our side.

In that case, we might want to support $start_time, $interval, and $end_time in addition to __start_time, __interval, and __end_time, so that we can move toward a consistent experience with $ only. I think that would be better than the user having to know both ways, going forward, but we can still support the old way for backwards compatibility

We can therefore update our Grafana plugin to support both and update our example scripts to use $

The equivalent with Grafana global variables are $__interval, $__from and $__to. I think these should be familiar to users because Grafana mentions these variables directly in their documentation.