grafana/k6 · error

grpc protocol does not support URL path

Error message

grpc protocol does not support URL path

What it means

The gRPC trace exporter is addressed by host:port only and cannot use an HTTP URL path. After parsing the otel config line, k6 rejects the combination proto=grpc with a non-empty urlPath with ErrInvalidGRPCWithURLPath. A URL like otel=https://host:4318/v1/traces sets proto=http and a urlPath; explicitly adding proto=grpc afterwards overrides the protocol but leaves the path set, which fails this check.

Solutions

1. Keep proto=http (or drop proto=) when the endpoint URL contains a path
2. For grpc, specify only host:port with no path — e.g. omit the URL and use otel=collector:4317,proto=grpc or plain --traces-output=otel
3. Point the gRPC exporter at the collector's 4317 port instead of the HTTP 4318 port

Example fix

# before
k6 run --traces-output='otel=https://collector:4318/v1/traces,proto=grpc' script.js
# after
k6 run --traces-output='otel=http://collector:4318/v1/traces,proto=http' script.js

// Wrapper: reject proto=grpc when the URL contains a path
if echo "$TRACES_OUTPUT" | grep -q 'proto=grpc' && echo "$TRACES_OUTPUT" | grep -Eq 'otel=https?://[^,]+/.'; then
  echo "grpc traces exporter cannot take a URL path; use proto=http" >&2; exit 1
fi

function grpcAcceptsTracesLine(line) {
  if (!line.includes('proto=grpc')) return true;
  const m = line.match(/otel=(https?:\/\/[^,]+)/);
  return !m || new URL(m[1]).pathname === '';
}

When it happens

Trigger: --traces-output='otel=https://collector:4318/v1/traces,proto=grpc' (URL with a path plus an explicit grpc protocol); any combination where the final params have proto=grpc and a URL path from a parsed http(s) URL.

Common situations: Copy-pasting an OTLP/HTTP collector endpoint (which always has /v1/traces) and forcing proto=grpc out of habit; mixing the URL form and the proto= option.

Related errors

• invalid protocol
• gRPC exporter endpoint is required
• invalid traces output
• invalid URL scheme
• unsupported exporter protocol

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/e434671ad8bd02cb. Report an issue: GitHub.

Appendix: source

Thrown at internal/lib/trace/otel.go:33

	sdktrace "go.opentelemetry.io/otel/sdk/trace"
	semconv "go.opentelemetry.io/otel/semconv/v1.20.0"
	"go.opentelemetry.io/otel/trace"
	"go.opentelemetry.io/otel/trace/noop"

	"go.k6.io/k6/v2/internal/lib/strvals"
)

const serviceName = "k6"

var (
	// ErrInvalidTracesOutput indicates that the defined traces output is not valid.
	ErrInvalidTracesOutput = errors.New("invalid traces output")
	// ErrInvalidProto indicates that the defined exporter protocol is not valid.
	ErrInvalidProto = errors.New("invalid protocol")
	// ErrInvalidURLScheme indicates that the defined exporter URL scheme is not valid.
	ErrInvalidURLScheme = errors.New("invalid URL scheme")
	// ErrInvalidGRPCWithURLPath indicates that an exporter using gRPC protocol does not support URL path.
	ErrInvalidGRPCWithURLPath = errors.New("grpc protocol does not support URL path")
)

type (
	tracerProvShutdownFunc func(ctx context.Context) error
)

// TracerProvider provides methods for tracers initialization and shutdown of the
// processing pipeline.
type TracerProvider struct {
	trace.TracerProvider
	shutdown tracerProvShutdownFunc
}

type tracerProviderParams struct {
	proto    string
	endpoint string
	urlPath  string
	insecure bool

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