Pin OTEL_EXPORTER_OTLP_PROTOCOL=http/protobuf

[prim-8]

Summary

opentelemetry-instrument defaults OTLP exporter protocol to grpc per the OTel spec, but the Dockerfile installs only the HTTP exporter. Without an explicit pin, runtime startup fails with:

RuntimeError: Requested component 'otlp_proto_grpc' not found
in entry point 'opentelemetry_traces_exporter'
Failed to auto initialize OpenTelemetry

The SDK then doesn't initialise — manual span calls become no-ops, the milter looks healthy, but no traces ship. Setting OTEL_EXPORTER_OTLP_PROTOCOL=http/protobuf (with :- so a deployer can still override) selects the right exporter.

Verified

docker build --build-arg INSTALL_DDTRACE=true --build-arg INSTALL_OTEL=true -t test .
docker run --rm \
  -e OTEL_TRACING_ENABLED=true \
  -e OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318 \
  -e OTEL_EXPORTER_OTLP_PROTOCOL=http/protobuf \
  test opentelemetry-instrument python3 -c '...'
# → SDK initialises, span created, exits 0
# → URLLib3Instrumentor / BotocoreInstrumentor / LoggingInstrumentor all attach

Test plan

• Build with INSTALL_OTEL=true and run opentelemetry-instrument — no otlp_proto_grpc not found error.
• Startup log shows OpenTelemetry tracing enabled (... protocol=http/protobuf).

[greptile-apps]

Greptile Summary

This PR fixes a runtime startup failure when OTEL_TRACING_ENABLED=true by pinning OTEL_EXPORTER_OTLP_PROTOCOL to http/protobuf in entrypoint.sh. The Dockerfile only installs opentelemetry-exporter-otlp-proto-http, but the OTel SDK defaults to gRPC, causing an unresolved entry-point error that silently drops all traces. The fix uses :- parameter expansion so deployers can still override the protocol, and adds the protocol to the startup log line for better observability.

Confidence Score: 5/5

Safe to merge — fixes a definite runtime failure with no regressions; all findings are P2 or lower.

The change is minimal, well-commented, and directly fixes a documented startup error. The :- default pattern preserves backward compatibility for deployers who want to override the protocol. Dockerfile confirms only the HTTP exporter is installed, validating the fix. No logic issues found.

No files require special attention.

Important Files Changed

Filename	Overview
milter/entrypoint.sh	Adds OTEL_EXPORTER_OTLP_PROTOCOL default (http/protobuf) and includes protocol in the startup log; fixes silent trace-drop when only the HTTP OTLP exporter is installed.

Sequence Diagram

sequenceDiagram
    participant E as entrypoint.sh
    participant SDK as opentelemetry-instrument
    participant Exp as OTLP HTTP Exporter

    E->>E: OTEL_TRACING_ENABLED=true
    E->>E: export OTEL_EXPORTER_OTLP_PROTOCOL=http/protobuf (default)
    E->>SDK: exec opentelemetry-instrument python3 milter.py
    SDK->>SDK: reads OTEL_EXPORTER_OTLP_PROTOCOL
    SDK->>Exp: loads opentelemetry-exporter-otlp-proto-http
    Exp-->>SDK: exporter ready
    SDK-->>E: process starts, traces ship to OTLP endpoint

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