The way that blackbox_exporter itself handles this (in Go) is to create a
fresh disposable registry for every request, inside the http handler:
https://github.com/prometheus/blackbox_exporter/blob/master/prober/handler.go#L125-L148
and then each probe request registers its metrics onto that registry, e.g.
https://github.com/prometheus/blackbox_exporter/blob/master/prober/icmp.go#L84-L88
I think this ought to be possible in Python too. I guess you would need to
call make_wsgi_app at the end of your handler, and then invoke it.
[Untested]
On Tuesday, 4 February 2025 at 16:57:03 UTC Elliott Balsley wrote:
> I’d like to build a multi-target exporter, similar to the blackbox
> exporter, where it takes an IP address as part of the URL path and uses
> that to collect metrics from hardware devices. This would be my first time
> writing a Prometheus exporter. From the Python client examples, I’ve
> created a CustomCollector class which collects only when scraped, running
> with start_http_server. But I can’t figure out how to access the URL path
> as a variable. Is that possible with this method or do I need to use a
> different web server like Flask or WSGI? A very simple example is below.
>
> from prometheus_client.core import GaugeMetricFamily, REGISTRYfrom
> prometheus_client.registry import Collectorfrom prometheus_client import
> start_http_serverimport randomimport time
> class CustomCollector(Collector):
> def collect(self):
> """Yield metrics only when scraped"""
>
> metrics = self.read_from_device()
> for metric in metrics:
> yield GaugeMetricFamily(metric['name'], 'help text',
> value=metric['value'])
>
> def read_from_device(self):
> """Blocking code that reads and parses data from hardware"""
>
> return [
> {'name': 'request_processing_seconds', 'value': random.random()},
> ]
>
> REGISTRY.register(CustomCollector())
>
> if __name__ == '__main__':
> start_http_server(port=8000)
> while True:
> time.sleep(86400)
>
>
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