Multiple processes metrics

[piotrkryger]

Summary

This PR covers functionality requested in #2761 :

• AllowMultipleProcessesMetrics configuration flag was added; it allows to return metrics from multiple processes via /metrics endpoint. By default its value is false and /metrics endpoint behaves as currently: when multiple processes match default process filters, no data is returned. When set to true, /metrics endpoint can return metrics of multiple processes, and:
  • all metrics returned by /metrics endpoint will contain additional labels: process_name and process_id. Those labels identify process which is the source of given metric
  • process_name label returns name of app pool for IIS processes (that is, when system process name is w3wp) and "regular" system process name for other processes

Release Notes Entry

Added option to track metrics of multiple processes via /metrics endpoint

[piotrkryger]

@dotnet-policy-service agree

[wiktork]

I think we'll need a separate filter for processes we monitor vs. processes we collect metrics for.

[wiktork]

Rather than keeping a list of tasks and checking their results, you could create continuations to StartMetricsPipelineForProcess that remove the pid from a set and remove the metrics from the store.

[wiktork]

These will likely need to be configurable

[wiktork]

Thank you for your contribution. I put some initial feedback in the PR, but please hold off on additional changes until we figure out some of these design points:

• Should we support multiple metrics on connect mode
• Configuration options: allow the same level of configurability but across N processes or keep all options the same.
• How do we extract a meaningful process name? Ideally we don't need specific understanding of w3wp or dotnet.

[piotrkryger]

Thank you for your feedback. I'll wait for your decisions.

(...)

• How do we extract a meaningful process name? Ideally we don't need specific understanding of w3wp or dotnet.

I suppose some extensibility for "process label factory" could be introduced, similarly to egress extensibility model.