Support configurable OTLP exporter protocol for traces and logs

[shuheiktgw]

Summary

• Currently, the OTLP protocol for the exporter is hardcoded to gRPC. However, some vendors do not support gRPC, so we would like to support other protocols as well and make the protocol configurable through standard environment variables.
• Add support for OTEL_EXPORTER_OTLP_PROTOCOL and per-signal env vars (OTEL_EXPORTER_OTLP_TRACES_PROTOCOL, OTEL_EXPORTER_OTLP_LOGS_PROTOCOL) to select gRPC, HTTP/protobuf, or HTTP/JSON transport for the OTLP exporter. Default remains gRPC for backward compatibility.

I'm new to Rust, so I'd really appreciate any feedback on my coding style 🙇

Test

Verified all 3 protocols deliver both traces and logs to a local OTEL Collector (v0.84.0).

Collector setup:

Save the following as /tmp/otel-debug-config.yaml:

receivers:
  otlp:
    protocols:
      grpc:
        endpoint: 0.0.0.0:4317
      http:
        endpoint: 0.0.0.0:4318

exporters:
  logging:
    loglevel: debug

service:
  pipelines:
    traces:
      receivers: [otlp]
      exporters: [logging]
    logs:
      receivers: [otlp]
      exporters: [logging]

Note: v0.84.0 uses logging exporter; the debug exporter is not yet available at this version.

docker run --rm -p 4317:4317 -p 4318:4318 \
  -v /tmp/otel-debug-config.yaml:/etc/otel-config.yaml \
  otel/opentelemetry-collector:0.84.0 \
  --config=/etc/otel-config.yaml

Prerequisite:

mkdir -p /tmp/qwdata

1. gRPC (default)

QW_ENABLE_OPENTELEMETRY_OTLP_EXPORTER=true \
OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4317 \
OTEL_EXPORTER_OTLP_PROTOCOL=grpc \
QW_DATA_DIR=/tmp/qwdata \
cargo run --manifest-path quickwit/Cargo.toml -p quickwit-cli -- run

2. HTTP/protobuf

QW_ENABLE_OPENTELEMETRY_OTLP_EXPORTER=true \
OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318 \
OTEL_EXPORTER_OTLP_PROTOCOL=http/protobuf \
QW_DATA_DIR=/tmp/qwdata \
cargo run --manifest-path quickwit/Cargo.toml -p quickwit-cli -- run

3. HTTP/JSON

QW_ENABLE_OPENTELEMETRY_OTLP_EXPORTER=true \
OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318 \
OTEL_EXPORTER_OTLP_PROTOCOL=http/json \
QW_DATA_DIR=/tmp/qwdata \
cargo run --manifest-path quickwit/Cargo.toml -p quickwit-cli -- run

What to verify in Collector stdout:

• TracesExporter + ResourceSpans output (traces received)
• LogsExporter + ResourceLog + LogRecord output (logs received)

[shuheiktgw]

Note that these environment variables are not supported by the Rust SDK, so we need to handle them manually.

open-telemetry/opentelemetry-rust#3363