Allow tracing sampleRate smaller than 1%

[dghubble]

Description:

Envoy Gateway's EnvoyProxy CustomResourceDefinition expects the tracing field's sampleRate to be an integer, allowing 0 to 100.

I'd like to keep tracing on, but sample perhaps 0.01% of traffic. This does not seem to be directly possible, although envoy-proxy itself seems to support float64 sample rates.

# desired
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: EnvoyProxy
spec:
  telemetry:
    tracing:
      sampleRate: 0.01
...

[optional Relevant Links:]

https://gateway.envoyproxy.io/latest/api/extension_types/#proxytelemetry

SamplingRate controls the rate at which traffic will be
selected for tracing if no prior sampling decision has been made.
Defaults to 100, valid values [0-100]. 100 indicates 100% sampling

[arkodg]

cc @zirain , we may have been trying to avoid using floats in the CRD in the past, but this is a legit use case, and recently the faultInjection API used floats

gateway/api/v1alpha1/fault_injection.go

Line 37 in dd1c66f

Percentage *float32 `json:"percentage,omitempty"`

[zirain]

TBH, is that real meaningful in real world?

[arkodg]

gateway-api's mirroring filter introduced an additional fraction field to solve this https://gateway-api.sigs.k8s.io/reference/spec/#gateway.networking.k8s.io%2fv1.HTTPRequestMirrorFilter, we could have something similar here

[dghubble]

is that real meaningful in real world?

With a lot of traffic, 1% is a ton of traces. A fraction would help because even with 0.01% is doesn't take long to find traces with errors or p99s worth looking into.

[zirain]

you may not get help from traing with a very low sample rate, you may need CEL based sampler.
With CEL based sampler, you're able to sample only response.code != 200.

[dghubble]

Im just looking to sample a smaller percentage of all traffic, not do expressions. Success traces still have value to me too

[zirain]

sgtm