Add schema_id, config_hash attributes to the apollo_router_session_count_total metric

[goto-bus-stop]

This adds attributes to the apollo_router_session_count_total metric, so customers can see if they have sessions that are keeping alive references to large amounts of previous router state after a configuration or schema change. This would help diagnose potential memory usage issues and inform our approach to dealing with that.

To do this the session_count_total instrument is refactored a bit; it was previously using a single global state value, now there can be multiple total session counts with different attributes alive at the same time.

For the schema_id, I just had to thread it through several layers of functions. For the config, I "invented" a new config hash (sha256 of JSON-serialized value).

This also fixes a bug that was introduced in 797a3be. In that commit the total session count is changed from a manual counter to a guard, but the guard was not moved into the tokio task properly, so it would immediately decrement. That change has not made it to a release luckily.

I'll mark this as a draft to add some tests for the metric to validate both this PR and the basic behaviour.

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Checklist

Complete the checklist (and note appropriate exceptions) before the PR is marked ready-for-review.

• Changes are compatible¹
• Documentation² completed
• Performance impact assessed and acceptable
• Tests added and passing³
  • Unit Tests
  • Integration Tests
  • Manual Tests

Exceptions

Note any exceptions here

Notes

Footnotes

1. It may be appropriate to bring upcoming changes to the attention of other (impacted) groups. Please endeavour to do this before seeking PR approval. The mechanism for doing this will vary considerably, so use your judgement as to how and when to do this. ↩

2. Configuration is an important part of many changes. Where applicable please try to document configuration examples. ↩

3. Tick whichever testing boxes are applicable. If you are adding Manual Tests, please document the manual testing (extensively) in the Exceptions. ↩

[github-actions]

@goto-bus-stop, please consider creating a changeset entry in /.changesets/. These instructions describe the process and tooling.

[router-perf]

CI performance tests

• connectors-const - Connectors stress test that runs with a constant number of users
• const - Basic stress test that runs with a constant number of users
• demand-control-instrumented - A copy of the step test, but with demand control monitoring and metrics enabled
• demand-control-uninstrumented - A copy of the step test, but with demand control monitoring enabled
• enhanced-signature - Enhanced signature enabled
• events - Stress test for events with a lot of users and deduplication ENABLED
• events_big_cap_high_rate - Stress test for events with a lot of users, deduplication enabled and high rate event with a big queue capacity
• events_big_cap_high_rate_callback - Stress test for events with a lot of users, deduplication enabled and high rate event with a big queue capacity using callback mode
• events_callback - Stress test for events with a lot of users and deduplication ENABLED in callback mode
• events_without_dedup - Stress test for events with a lot of users and deduplication DISABLED
• events_without_dedup_callback - Stress test for events with a lot of users and deduplication DISABLED using callback mode
• extended-reference-mode - Extended reference mode enabled
• large-request - Stress test with a 1 MB request payload
• no-tracing - Basic stress test, no tracing
• reload - Reload test over a long period of time at a constant rate of users
• step-jemalloc-tuning - Clone of the basic stress test for jemalloc tuning
• step-local-metrics - Field stats that are generated from the router rather than FTV1
• step-with-prometheus - A copy of the step test with the Prometheus metrics exporter enabled
• step - Basic stress test that steps up the number of users over time
• xlarge-request - Stress test with 10 MB request payload
• xxlarge-request - Stress test with 100 MB request payload

[goto-bus-stop]

Interestingly this metric no longer exists in router 2.0. Instead there is a http.server.active_requests metric that we could likely attach these attributes to.

[goto-bus-stop]

I'm going to redo this after fixing the apollo_router_session_count_total metric.