What causes "{} contains invalid label format: {}" in quickwit-oss/quickwit?

Fix QW_METRICS_LABELS so every token is name=value, e.g. QW_METRICS_LABELS='env=prod,region=us-east-1'.

{} contains invalid label format: {}

Error message

{} contains invalid label format: {}

What it means

init_metrics_labels_env_var parses the QW_METRICS_LABELS environment variable, which must be a comma-separated list of name=value pairs. parse_metrics_labels fails on any comma-separated token that lacks an '=' separator, naming the offending token in the message.

Source

Thrown at quickwit/quickwit-metrics/src/lib.rs:429

    LABELS_ENV_VAR.get_or_init(|| parsed_labels.into_boxed_slice());

    Ok(())
}

// The format of the environment variable is:
// QW_METRICS_LABELS="environment=test,region=us-east-1,foo=bar"
fn parse_metrics_labels(labels: &str) -> anyhow::Result<Vec<Label>> {
    let mut parsed_labels: Vec<Label> = Vec::new();
    if labels.trim().is_empty() {
        return Ok(parsed_labels);
    }

    const LABELS_SEPARATOR: char = ',';
    const KEY_VALUE_SEPARATOR: char = '=';

    for label in labels.split(LABELS_SEPARATOR) {
        let (name, value) = label.split_once(KEY_VALUE_SEPARATOR).ok_or_else(|| {
            anyhow::anyhow!(
                "{} contains invalid label format: {}",
                QW_METRICS_LABELS_ENV_VAR,
                label
            )
        })?;
        let name = name.trim();
        if name.is_empty() {
            anyhow::bail!(
                "{} contains an empty label name: {}",
                QW_METRICS_LABELS_ENV_VAR,
                label
            );
        }
        let value = value.trim();
        if value.is_empty() {
            anyhow::bail!(
                "{} contains an empty label value: {}",
                QW_METRICS_LABELS_ENV_VAR,

View on GitHub (pinned to a39730c5cd)

Solutions

Fix QW_METRICS_LABELS so every token is name=value, e.g. QW_METRICS_LABELS='env=prod,region=us-east-1'.
Remove empty or malformed tokens (a trailing comma creates an empty token — though empty input itself is accepted).
Quote carefully in shell: use single quotes to avoid shell mangling '=' or spaces.

Example fix

// before
export QW_METRICS_LABELS="env=prod region"
// after
export QW_METRICS_LABELS="env=prod,region=us-east-1"

Defensive patterns

Strategy: validation

Validate before calling

let labels = std::env::var("QW_METRICS_LABELS").unwrap_or_default();
for token in labels.split(',').filter(|t| !t.is_empty()) {
    assert!(token.contains('='), "invalid label token: {}", token);
}

Try / catch

if let Err(e) = init_metrics_labels_env_var() {
    eprintln!("invalid QW_METRICS_LABELS: {e}; expected name=value pairs comma-separated");
}

Prevention

Use single-quoted shell values: QW_METRICS_LABELS='env=prod,region=us-east-1'.
Validate the env var in your deployment pipeline before rollout.
Remember format is strictly name=value tokens joined by commas.

When it happens

Trigger: Setting QW_METRICS_LABELS to a value like 'env=prod,region' (a token without '=') and calling init_metrics_labels_env_var at startup.

Common situations: Typos in the env var value (space instead of '=', missing value); copy-pasting Prometheus label syntax with different separators; forgetting that pairs are comma-separated with no quoting.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of quickwit-oss/quickwit@a39730c5cd (2026-09-08). Data as JSON: /api/errors/91add1a1b5896606. Report an issue: GitHub.