Support pushing traces to otel collector

[adam-cattermole]

This adds support to push traces to an otel collector, configured via new command line options, --tracing-host and --tracing-port.

Currently this is configured to use grpc without TLS however this could be added as a follow up.

Verification:

For this example I'm running Redis as the datastore to verify.

Run Redis service

docker run --rm -it -p 6379:6379 redis

Run Jaeger with OTLP

docker run --rm -it --name jaeger -e COLLECTOR_OTLP_ENABLED=true -p 16686:16686 -p 4317:4317 -p 4318:4318 jaegertracing/all-in-one:latest

firefox -private-window "localhost:16686"

Build and run from this branch

cargo build --bin limitador-server

./target/debug/limitador-server --tracing-endpoint rpc://localhost:4317 -vvvv --grpc-reflection-service limitador-server/sandbox/limits.yaml redis redis://127.0.0.1

Send Requests

grpcurl -plaintext -d @ 127.0.0.1:8081 envoy.service.ratelimit.v3.RateLimitService.ShouldRateLimit <<EOM
{
    "domain": "test_namespace",
    "hits_addend": 1,
    "descriptors": [
        {
            "entries": [
                {
                    "key": "req.method",
                    "value": "POST"
                }
            ]
        }
    ]
}
EOM

See the spans for the requests under the limitador-server service in the jaeger ui:

[eguzki]

what is this doing? (when exporter is not being defined)

[adam-cattermole]

The tracing package is being used for the standard logging since #250 - if tracing_host is unset we ensure that the fmt_layer is still applied so we get log output on stdout. Only if it's set we apply the telemetry_layer as well which is sending to the collector

[alexsnaps]

I think I'd want to align that with authorino's way of configuring...

[adam-cattermole]

I've had a look and this .with_protocol doesn't actually effect the behaviour. Either we use .tonic() and it's grpc, or we use .http() and provide our choice of http client. For now I've moved to a --tracing-endpoint option which contains scheme the same as authorino, but it won't use http if provided unless we check the scheme and configure an http client

[alexsnaps]

LGTM, modulo the unnecessary diffs, but I'll let you be the judge of their faith