grafana/k6 · error

invalid protocol

Error message

invalid protocol

What it means

Within the --traces-output=otel=... configuration line, the proto= option selects the exporter transport and accepts exactly 'http' or 'grpc' (default 'grpc'). params.parseProto returns ErrInvalidProto wrapped as "couldn't parse the otel proto" for any other value. Note this is k6's own parameter name — OTel SDK spellings like 'http/protobuf' are not accepted here.

Solutions

1. Use proto=http or proto=grpc exactly (lowercase)
2. Omit proto= entirely to get the default grpc transport
3. If you only need an HTTP endpoint, pass the URL form: otel=http://host:4318/v1/traces (this implies proto=http)

Example fix

# before
k6 run --traces-output='otel=127.0.0.1:4318/v1/traces,proto=http/protobuf' script.js
# after
k6 run --traces-output='otel=http://127.0.0.1:4318/v1/traces,proto=http' script.js

// Shell
proto="$(echo "$TRACES_OUTPUT" | tr ',' '\n' | grep '^proto=' | cut -d= -f2)"
if [ -n "$proto" ] && [ "$proto" != "http" ] && [ "$proto" != "grpc" ]; then
  echo "proto= must be http or grpc" >&2; exit 1
fi

function isValidTraceProto(p) {
  return p === '' || p === 'http' || p === 'grpc';
}

When it happens

Trigger: Passing --traces-output='otel=...,proto=http/protobuf' (OTel SDK convention instead of k6's 'http'); proto=grpc-web, proto=h2, or any typo such as proto=GRPC (case-sensitive).

Common situations: Copying values from OTEL_EXPORTER_OTLP_PROTOCOL docs or collector configs into k6's traces flag; assuming protocol names are case-insensitive.

Related errors

• grpc protocol does not support URL path
• invalid traces output
• invalid URL scheme
• unsupported exporter protocol
• failed to append root certificate to the pool

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/f16b59a45efced3c. Report an issue: GitHub.

Appendix: source

Thrown at internal/lib/trace/otel.go:29

	"go.opentelemetry.io/otel/exporters/otlp/otlptrace"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp"
	"go.opentelemetry.io/otel/sdk/resource"
	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 {

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