quarkusio/quarkus · error · IllegalArgumentException

Unsupported OTLP protocol %s specified. Please check `quarku

Error message

Unsupported OTLP protocol %s specified. Please check `quarkus.otel.exporter.otlp.logs.protocol` property

What it means

The OTLP log exporter builder only supports `grpc` and `http/protobuf` protocols. If `quarkus.otel.exporter.otlp.logs.protocol` holds any other value, the recorder throws IllegalArgumentException (then wrapped as 'Unable to install OTLP Exporter'). This guards against silently configuring an exporter that cannot send data.

Source

Thrown at extensions/opentelemetry/runtime/src/main/java/io/quarkus/opentelemetry/runtime/exporter/otlp/OTelExporterRecorder.java:322

                                new HttpExporter(
                                        ComponentId.generateLazy(
                                                StandardComponentId.ExporterType.OTLP_HTTP_LOG_EXPORTER),
                                        new VertxHttpSender(
                                                baseUri,
                                                VertxHttpSender.LOGS_PATH,
                                                determineCompression(logsConfig),
                                                logsConfig.timeout(),
                                                populateTracingExportHttpHeaders(logsConfig),
                                                exportAsJson ? "application/json" : "application/x-protobuf",
                                                new HttpClientOptionsConsumer(logsConfig, baseUri, tlsConfigurationRegistry),
                                                vertx.get()),
                                        MeterProvider::noop,
                                        InternalTelemetryVersion.LATEST,
                                        baseUri,
                                        false),
                                memoryMode);
                    } else {
                        throw new IllegalArgumentException(String.format("Unsupported OTLP protocol %s specified. " +
                                "Please check `quarkus.otel.exporter.otlp.logs.protocol` property", protocol));
                    }

                } catch (IllegalArgumentException iae) {
                    throw new IllegalStateException("Unable to install OTLP Exporter", iae);
                }
                return logRecordExporter;
            }
        };
    }

    private static DefaultAggregationSelector aggregationResolver(OtlpExporterMetricsConfig metricsConfig) {
        String defaultHistogramAggregation = metricsConfig.defaultHistogramAggregation()
                .map(s -> s.toLowerCase(Locale.ROOT))
                .orElse("explicit_bucket_histogram");

        DefaultAggregationSelector aggregationSelector;
        if (defaultHistogramAggregation.equals("explicit_bucket_histogram")) {

View on GitHub (pinned to e1c734241f)

Solutions

Set `quarkus.otel.exporter.otlp.logs.protocol=http/protobuf`
Or set it to `grpc`
Verify exact spelling and case of the protocol value
Check you edited the `logs.protocol` key and not another signal's

Example fix

# before
quarkus.otel.exporter.otlp.logs.protocol=http/json
# after
quarkus.otel.exporter.otlp.logs.protocol=http/protobuf

Defensive patterns

Strategy: validation

Validate before calling

String p = ConfigProvider.getConfig().getValue("quarkus.otel.exporter.otlp.logs.protocol", String.class);
if (!"grpc".equals(p) && !"http/protobuf".equals(p)) {
    throw new IllegalArgumentException("quarkus.otel.exporter.otlp.logs.protocol must be grpc or http/protobuf, got: " + p);
}

Type guard

static boolean isSupportedOtlpProtocol(String p) {
    return "grpc".equals(p) || "http/protobuf".equals(p);
}

Try / catch

try {
    app.start();
} catch (IllegalStateException e) {
    if (e.getMessage().contains("Unable to install OTLP Exporter")) {
        LOG.error("Check quarkus.otel.exporter.otlp.logs.protocol (grpc | http/protobuf): " + e.getCause().getMessage());
    }
}

Prevention

Use exactly `grpc` or `http/protobuf` for the logs protocol
Don't confuse with upstream OTel values like `http/json`
Verify edits target the `logs.protocol` key, not metrics/traces
Boot-test with the final config profile

When it happens

Trigger: Setting `quarkus.otel.exporter.otlp.logs.protocol` to anything besides `grpc` or `http/protobuf`, e.g. `http/json`, `otlp`, `grpc+tls`, or a misspelled value.

Common situations: Typos in properties files; values copied from the OTLP spec (`http/json` exists upstream but is not supported by Quarkus' exporters); mixing up metrics and logs protocol keys.

Related errors

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/cbb71bfe8bedf653. Report an issue: GitHub.