[ Bugfix ] Fix Prometheus Metrics With zeromq Frontend

[robertgshaw2-redhat]

SUMMARY:

• Prometheus metrics are broken in v0.5.4 due to zeromq multiprocessing frontend
• Set PROMETHEUS_MULTIPROC_DIR environment variable to enable multiprocessing mode (note, this must be set before prometheus_client is imported. So we lazily init anything that imports prometheus_client
• Use tempfile for PROMETHEUS_MULTIPROC_DIR
• Adds testing for metrics via the OpenAI endpoint (w/ more correctness tests)
• Convert Info metrics to use Gauge set to 1

PERFORMANCE:
TPOT L8B H100 | 500 input | 150 output | 10QPS:

• pr: 47.29
• main: 45.42

There is a slight performance hit here. I think we should try to optimize prometheus in a separate effort where we move prometheus out of the main asyncio event loop

NOTES:

• using the mp feature of prometheus_client comes with some additional complexity / limitations (see https://prometheus.github.io/client_python/multiprocess/)
• cpu and process metrics no longer work, e.g. we no longer get this info:

# HELP python_gc_objects_collected_total Objects collected during gc
# TYPE python_gc_objects_collected_total counter
python_gc_objects_collected_total{generation="0"} 11803.0
python_gc_objects_collected_total{generation="1"} 6448.0
python_gc_objects_collected_total{generation="2"} 3557.0
# HELP python_gc_objects_uncollectable_total Uncollectable objects found during GC
# TYPE python_gc_objects_uncollectable_total counter
python_gc_objects_uncollectable_total{generation="0"} 0.0
python_gc_objects_uncollectable_total{generation="1"} 0.0
python_gc_objects_uncollectable_total{generation="2"} 0.0
# HELP python_gc_collections_total Number of times this generation was collected
# TYPE python_gc_collections_total counter
python_gc_collections_total{generation="0"} 1546.0
python_gc_collections_total{generation="1"} 139.0
python_gc_collections_total{generation="2"} 11.0
# HELP python_info Python platform information
# TYPE python_info gauge
python_info{implementation="CPython",major="3",minor="8",patchlevel="19",version="3.8.19"} 1.0
# HELP process_virtual_memory_bytes Virtual memory size in bytes.
# TYPE process_virtual_memory_bytes gauge
process_virtual_memory_bytes 1.24949229568e+011
# HELP process_resident_memory_bytes Resident memory size in bytes.
# TYPE process_resident_memory_bytes gauge
process_resident_memory_bytes 7.277645824e+09
# HELP process_start_time_seconds Start time of the process since unix epoch in seconds.
# TYPE process_start_time_seconds gauge
process_start_time_seconds 1.72315136919e+09
# HELP process_cpu_seconds_total Total user and system CPU time spent in seconds.
# TYPE process_cpu_seconds_total counter
process_cpu_seconds_total 38.27
# HELP process_open_fds Number of open file descriptors.
# TYPE process_open_fds gauge
process_open_fds 101.0
# HELP process_max_fds Maximum number of open file descriptors.
# TYPE process_max_fds gauge
process_max_fds 1.048576e+06

FIX #7188

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[github-actions]

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[DarkLight1337]

Would be great if we could add a test to check that vLLM-specific metrics are returned in the /metrics endpoint.

[robertgshaw2-redhat]

Would be great if we could add a test to check that vLLM-specific metrics are returned in the /metrics endpoint.

100% - poor test coverage here caused us to miss this impact in v0.5.4

[robertgshaw2-redhat]

@njhill @simon-mo - this should be ready to merge. There is a bit of a perf hit vs main, but I think we should go ahead and land this because it is the simplest approach by far

I will work to address the overhead of prometheus in a separate workstream. Specifically, promtheus should not be running in the main event loop.

[njhill]

Thanks @robertgshaw2-neuralmagic, just a couple of comments

[njhill]

Per @thekuffs's comment, I think we could actually keep the info metrics, just use a gauge explicitly here?

[njhill]

@robertgshaw2-neuralmagic looks like the CI has a legit failure too... I'm looking to see what's going on there

[robertgshaw2-redhat]

@robertgshaw2-neuralmagic looks like the CI has a legit failure too... I'm looking to see what's going on there

My b. GitHub was down. Will look

[njhill]

LGTM thanks @robertgshaw2-neuralmagic!