Add Feast Serving gRPC call metrics

[ashwinath]

What this PR does / why we need it:
Feast Serving does not expose grpc prometheus metrics.

Which issue(s) this PR fixes:
None

Fixes #

Does this PR introduce a user-facing change?:
None

gRPC calls in feast serving now exposes prometheus metrics.

[feast-ci-bot]

Hi @ashwinath. Thanks for your PR.

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[ashwinath]

/assign @davidheryanto

[woop]

Which issue is this in relation to?

[ashwinath]

It was an issue @davidheryanto brought up regarding Feast Serving needing to expose a metric to count erronous requests. As of now, the stats from the gRPC calls were not captured, but rather the methods it invoked were captured; missing out on the gRPC error codes. This PR adds the gRPC codes into the labels of feast_serving_request_latency_ms.

[davidheryanto]

Yeah currently for Feast Serving these are the metrics we record
https://github.com/gojek/feast/blob/master/serving/src/main/java/feast/serving/util/Metrics.java#L22

But it's missing metric about errors, which is quite important because it may indicate something wrong with Feast serving GRPC servers. So I think we should also include GRPC status code label to the metric https://github.com/grpc/grpc/blob/master/doc/statuscodes.md

So we can identify how many request Feast serving failed to handle due to different reasons.

[ashwinath]

Hi, I split them into two metrics. Load tested with 20 records

ghz --insecure \
    --call feast.serving.ServingService/GetOnlineFeatures localhost:6566 \
    --concurrency=10 \
    --qps=1000 \
    --total=10000 \
    --connections=1 \
    --data="{
        "'"'"features"'"'": {
          "'"'"project"'"'": "'"'"your_project_name"'"'",
          "'"'"name"'"'": "'"'"city"'"'",
          "'"'"version"'"'": 1
        },
        "'"'"entity_rows"'"'": [
            {
                "'"'"fields"'"'": {
                    "'"'"driver_id"'"'": {
                        "'"'"int64_val"'"'": 1234
                    }
                }
            }
        ]
    }"

Hovering around P95: 4ms, P99: 5ms for both master branch and this PR.

Similar results for 2000 QPS also

[woop]

Looks much better, thanks @ashwinath and @davidheryanto

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ashwinath, woop

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[woop]

/ok-to-test

[woop]

/test test-end-to-end-batch

[ches]

A test might be good, but if we feel this looks like overkill for a small metrics interceptor, then I think it'd be nice to mention the method name label in the class Javadoc with an example of what it looks like.

[ches]

Bikeshedding on naming if you'll bear with me… it's more about request/response metrics than monitoring, monitoring would be what you might externally do with the metrics ☺️

Also I wonder if anyone would object to dropping the Grpc prefix, I imagine everything in the interceptors package will be a gRPC interceptor so perhaps it's redundant. What do you think of:

Suggested change

	public class GrpcMonitoringInterceptor implements ServerInterceptor {
	public class RequestMetricsInterceptor implements ServerInterceptor {

[davidheryanto]

Yes sounds reasonable to me. I think we need to create a new PR?

Although the sample library for integrating Prometheus with GRPC in Java uses the monitoring term as well :)
https://github.com/grpc-ecosystem/java-grpc-prometheus/tree/master/src/main/java/me/dinowernli/grpc/prometheus

I guess as long as we're consistent.

[woop]

/lgtm