Error while running action plugin 'alerta_prometheus': name 'USE_AM_EXTERNALURL_FOR_SILENCES' is not defined (500)

Issue Summary When using the prometheus plugin, I get an error, as mentionned in the title: Error while running action plugin 'alerta_prometheus': name 'USE_AM_EXTERNALURL_FOR_SILENCES' is not defined (500)

The problem seem to be this:

the variable set is: ALERTMANAGER_USE_EXTERNALURL_FOR_SILENCES = os.environ.get('ALERTMANAGER_USE_EXTERNALURL_FOR_SILENCES') or app.config.get('ALERTMANAGER_USE_EXTERNALURL_FOR_SILENCES',False)

but the plugin is looking for this:

        # if alertmanager is clustered behind a load balancer that mirrors requests we should prefer to create one silence
        # rather than many
        if USE_AM_EXTERNALURL_FOR_SILENCES:

I tried to change the condition to ALERTMANAGER_USE_EXTERNALURL_FOR_SILENCES and it seem to work fine so far

Environment

OS: LLinux
API version: 8.6.5
Deployment: self-hosted
For self-hosted, WSGI environment: nginx/uwsgi
Database: MongoDB
Server config: Auth enabled? Yes Auth provider? Basic Customer views? No (or provide the /config endpoint output)
web UI version: 6.7.0
CLI version: na

To Reproduce Steps to reproduce the behavior:

Go to the web ui
Try to ackonowledge an Alertmanager alert. '
See error (include command output)

Traceback (most recent call last): File "/opt/alerta/lib64/python3.6/site-packages/flask/app.py", line 1516, in full_dispatch_request rv = self.dispatch_request() File "/opt/alerta/lib64/python3.6/site-packages/flask/app.py", line 1502, in dispatch_request return self.ensure_sync(self.view_functions[rule.endpoint])(req.view_args) File "/opt/alerta/lib64/python3.6/site-packages/flask_cors/decorator.py", line 128, in wrapped_function resp = make_response(f(*args, *kwargs)) File "/opt/alerta/lib64/python3.6/site-packages/alerta/auth/decorators.py", line 90, in wrapped return f(args, kwargs) File "/opt/alerta/lib64/python3.6/site-packages/alerta/models/metrics.py", line 258, in wrapped response = f(*args, *kwargs) File "/opt/alerta/lib64/python3.6/site-packages/alerta/utils/response.py", line 18, in decorated return func(args, **kwargs) File "/opt/alerta/lib64/python3.6/site-packages/alerta/views/alerts.py", line 173, in action_alert raise ApiError(str(e), 500)

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alerta / alerta-contrib

Error while running action plugin 'alerta_prometheus': name 'USE_AM_EXTERNALURL_FOR_SILENCES' is not defined (500) #379