denoland/deno · error · anyhow::Error

Invalid value for…

Error message

Invalid value for OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE: {}

What it means

When telemetry is enabled, Deno reads OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE to pick the metric temporality: 'cumulative' (default, also when unset), 'delta', or 'lowmemory'. The value is lowercased before matching, so case does not matter, but anything other than those three strings (after lowercasing) fails telemetry init.

Solutions

1. Set the variable to cumulative, delta, or lowmemory (any case; exact spelling, no separator)
2. Unset it to get cumulative
3. Strip trailing newlines/whitespace when injecting via scripts: OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE=$(printf %s "$v") or use tr -d '\n'

Example fix

# before
export OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE=low_memory  # -> Invalid value
deno run --otel app.ts

# after
export OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE=lowmemory
deno run --otel app.ts

const ALLOWED = new Set(["cumulative", "delta", "lowmemory"]);
const pref = Deno.env.get("OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE")?.toLowerCase().trim();
if (pref && !ALLOWED.has(pref)) {
  throw new Error(`Temporality must be cumulative|delta|lowmemory, got '${pref}'`);
}

const { code, stderr } = await new Deno.Command("deno", { args: ["run", "--otel", "app.ts"] }).output();
if (code !== 0 && new TextDecoder().decode(stderr).includes("TEMPORALITY_PREFERENCE")) {
  delete env.OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE; // default cumulative
  // relaunch
}

When it happens

Trigger: Running with --otel with the variable set to e.g. 'cumulative-delta', 'low_memory' (underscore instead of no separator), 'DELTA' works but ' delta' with internal space does not (only leading/trailing... note the value is not trimmed here, unlike OTEL_TRACES_SAMPLER), or other OTel-adjacent spellings.

Common situations: The spec name is 'lowmemory' (one word) but developers write 'low_memory' or 'low-memory'; CI injecting values with trailing newline from command substitution $(cat file); copying Prometheus-oriented config expecting 'delta' naming variants.

Understand the failure class

Background: "is not a valid" / "Invalid ... value" environment variable errors: how libraries validate env vars and what to do when they reject yours — this error's family across 48 libraries.

Related errors

• Env var OTEL_EXPORTER_OTLP_PROTOCOL specifies an…
• Env var OTEL_TRACES_SAMPLER specifies an unsupported sampler
• Failed to read env var OTEL_EXPORTER_OTLP_PROTOCOL
• must be unset or set to 1
• failed to set otel globals

AI-assisted analysis of denoland/deno@9ad36f7a2c (2026-08-20). Data as JSON: /api/errors/6958384bb9568b8d. Report an issue: GitHub.

Appendix: source

Thrown at ext/telemetry/lib.rs:1311

        format!("{}-{}", rt_config.runtime_version, sdk_version),
      ),
    ])
    .build();

  // The OTLP endpoint is automatically picked up from the
  // `OTEL_EXPORTER_OTLP_ENDPOINT` environment variable. Additional headers can
  // be specified using `OTEL_EXPORTER_OTLP_HEADERS`.

  let temporality_preference = sys
    .env_var("OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE")
    .ok()
    .map(|s| s.to_lowercase());
  let temporality = match temporality_preference.as_deref() {
    None | Some("cumulative") => Temporality::Cumulative,
    Some("delta") => Temporality::Delta,
    Some("lowmemory") => Temporality::LowMemory,
    Some(other) => {
      return Err(deno_core::anyhow::anyhow!(
        "Invalid value for OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE: {}",
        other
      ));
    }
  };

  let (span_processor, meter_provider, log_processor) = if use_console_exporter
  {
    let span_exporter = console_exporter::ConsoleSpanExporter::new();
    let mut span_processor =
      BatchSpanProcessor::builder(span_exporter, OtelSharedRuntime).build();
    span_processor.set_resource(&resource);

    let metric_exporter =
      console_exporter::ConsoleMetricExporter::new(temporality);
    let metric_reader = DenoPeriodicReader::new(sys, metric_exporter);
    let meter_provider = SdkMeterProvider::builder()
      .with_reader(metric_reader)

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