Bug 2133027

Contents originally posted in upstream issue tracker at https://bugs.launchpad.net/aodh/+bug/1946793

~~~~

On gnocchi API docs, there are 2 API methods to aggregate metrics

1. /v1/aggregation/metric?

See: https://gnocchi.osci.io/rest.html#aggregation-across-metrics-deprecated

This one is deprecated

2. /v1/aggregates?

See: https://gnocchi.osci.io/rest.html#dynamic-aggregates

aodh uses the 1st one to aggregate metrics, for example:

```
        if isinstance(start, datetime.datetime):
            start = start.isoformat()
        if isinstance(stop, datetime.datetime):
            stop = stop.isoformat()

        params = dict(start=start, stop=stop, aggregation=aggregation,
                      reaggregation=reaggregation, granularity=granularity,
                      needed_overlap=needed_overlap, groupby=groupby,
                      refresh=refresh, resample=resample, fill=fill)
        if query is None:
            for metric in metrics:
                self._ensure_metric_is_uuid(metric)
            params['metric'] = metrics
            measures = self._get("v1/aggregation/metric",
                                 params=params).json()
```

aodh doesn't work properly in our production environment after upgraded to Ussuri.

When there is only 1 instance, aodh works properly and alarms can be triggered when the load on the instance is higher than the threshold.

However, after the stack is scaled up, and the second instance is created. The average cpu usage got from gnocchi by aodh evaluator is not correct. The metric measures are negative sometimes.

I manually pulled metrics with gnocchi command

The aggregation of metrics is correct with command

```
openstack metric aggregates
```

It uses new API in the backend

The aggregation of metrics is not correct with command

```
openstack metric measures aggregation
```

It uses the deprecated API which aodh is using.