What causes "Failed to fetch trace from backend" in openzipkin/zipkin?

Verify the trace still exists: open it in the UI or curl GET /api/v2/trace/{traceId} and expect 200

openzipkin/zipkin · error · Error

Failed to fetch trace from backend

Error message

Failed to fetch trace from backend

What it means

Thrown in zipkin-lens's TracePage HeaderMenu when the browser fetch of the raw trace JSON (GET /api/v2/trace/{traceId}) returns a non-OK HTTP status. The archive flow needs the raw JSON from the backend because it is not cached in the browser, so a failed fetch aborts archiving with this error.

Source

Thrown at zipkin-lens/src/components/TracePage/Header/HeaderMenu.tsx:63

    : undefined;

  const handleMenuButtonClick = (
    event: React.MouseEvent<HTMLButtonElement>,
  ) => {
    setAnchorEl(event.currentTarget);
  };

  const handleMenuClose = () => {
    setAnchorEl(null);
  };

  const handleArchiveButtonClick = useCallback(() => {
    // We don't store the raw json in the browser yet, so we need to make an
    // HTTP call to retrieve it again.
    fetch(`${api.TRACE}/${trace.traceId}`)
      .then((response) => {
        if (!response.ok) {
          throw new Error('Failed to fetch trace from backend');
        }
        return response.json();
      })
      .then((json) => {
        // Add zipkin.archived tag to root span
        /* eslint-disable-next-line no-restricted-syntax */
        for (const span of json) {
          if ('parentId' in span === false) {
            const tags = span.tags || {};
            tags['zipkin.archived'] = 'true';
            span.tags = tags;
            break;
          }
        }
        return json;
      })
      .then((json) => {
        return fetch(archivePostUrl, {

View on GitHub (pinned to 878ce2a1fa)

Solutions

Verify the trace still exists: open it in the UI or curl GET /api/v2/trace/{traceId} and expect 200
If it returns 404, the trace expired from storage — re-produce the trace or increase storage retention
Check server/proxy logs and the browser network tab for 401/403/5xx and fix routing or auth for the /api path
Retry after transient backend errors; fetch again before re-clicking Archive

Defensive patterns

Strategy: retry

Validate before calling

// check the trace still exists before offering/attempting archive
const res = await fetch(`${api.TRACE}/${trace.traceId}`);
if (!res.ok) {
  // 404 => trace evicted from storage; 5xx => backend issue
  throw new Error(`Trace not available (HTTP ${res.status})`);
}

Try / catch

try {
  const response = await fetch(`${api.TRACE}/${trace.traceId}`);
  if (!response.ok) throw new Error(`Fetch trace failed (HTTP ${response.status})`);
  const json = await response.json();
} catch (err) {
  // 404 is permanent (retention); 5xx/network may be transient -> one retry max
  if (isTransient(err)) await retryOnce();
  else showUserError('Trace no longer available in the backend');
}

Prevention

Disable/hide the Archive button for traces older than the storage retention window
Surface the HTTP status in the alert so users can distinguish 404 from backend failure
Keep the Lens base URL and proxy config pointing at a reachable Zipkin server

When it happens

Trigger: Clicking 'Archive Trace' in the Lens UI when the trace has been dropped from storage (e.g. past the retention/lookback window) and the API returns 404; the Zipkin server or proxy in front of it returns 401/403/500; a misconfigured base URL so the request 404s; transient network failure making response.ok false.

Common situations: Trying to archive an old trace that storage (in-memory, MySQL, ES with TTL) already evicted; running Lens against a reverse proxy that blocks or rewrites /api routes; server restart with in-memory storage wiping all traces.

Related errors

AI-assisted analysis of openzipkin/zipkin@878ce2a1fa (2026-08-14). Data as JSON: /api/errors/927924e231c358b5. Report an issue: GitHub.