thanos-io/thanos · error

request config against

Error message

request config against %s

What it means

ConfiguredFlags performs the HTTP GET to /api/v1/status/flags using the client's Do method; when the request fails at the transport level (connection refused, DNS failure, timeout, TLS error), the error is wrapped with 'request config against <url>' naming the exact URL attempted.

Solutions

1. Check connectivity to the URL in the error: curl http://prometheus:9090/api/v1/status/flags
2. Verify the Prometheus address/port in configuration
3. Check DNS resolution and NetworkPolicies/firewall rules
4. Increase the request context timeout if deadlines are too short
5. Fix TLS certificates/CA config if the endpoint uses HTTPS

Example fix

// before
--prometheus.url=http://localhost:9090   # sidecar runs in another pod
// after (kubernetes)
--prometheus.url=http://prometheus-linked.default.svc:9090

conn, err := net.DialTimeout("tcp", "prometheus:9090", 2*time.Second)
if err != nil {
    return fmt.Errorf("prometheus unreachable before request: %w", err)
}
conn.Close()

flags, err := client.ConfiguredFlags(ctx, u)
if err != nil {
    if isNetError(err) { // strings.Contains "connect", "refused", "timeout"
        // retry with exponential backoff
    }
    return err
}

When it happens

Trigger: c.Do(req.WithContext(ctx)) returns a non-nil error — Prometheus unreachable, wrong host/port, connection refused, TLS handshake failure, or context deadline exceeded during the call. Called by an anonymous caller fetching Prometheus flags.

Common situations: Prometheus not running or listening on a different port; DNS/service name wrong inside Kubernetes ('http://prometheus:9090' vs actual service); network policy blocking the sidecar; mTLS/TLS misconfiguration; request canceled by context timeout.

Understand the failure class

Background: ECONNREFUSED and "connection refused" / "could not connect to server" errors: what they mean and how to fix them — this error's family across 44 libraries.

Related errors

• failed to validate prometheus flags
• perform request against
• read query instant response
• read query range response
• request metric against

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/f260c6f566b6d8aa. Report an issue: GitHub.

Appendix: source

Thrown at pkg/promclient/promclient.go:306

}

// ConfiguredFlags returns configured flags from /api/v1/status/flags Prometheus endpoint.
// Added to Prometheus from v2.2.
func (c *Client) ConfiguredFlags(ctx context.Context, base *url.URL) (Flags, error) {
	u := *base
	u.Path = path.Join(u.Path, "/api/v1/status/flags")

	req, err := http.NewRequest(http.MethodGet, u.String(), nil)
	if err != nil {
		return Flags{}, errors.Wrap(err, "create request")
	}

	span, ctx := tracing.StartSpan(ctx, "/prom_flags HTTP[client]")
	defer span.Finish()

	resp, err := c.Do(req.WithContext(ctx))
	if err != nil {
		return Flags{}, errors.Wrapf(err, "request config against %s", u.String())
	}
	defer runutil.ExhaustCloseWithLogOnErr(c.logger, resp.Body, "query body")

	b, err := io.ReadAll(resp.Body)
	if err != nil {
		return Flags{}, errors.New("failed to read body")
	}

	switch resp.StatusCode {
	case 404:
		return Flags{}, ErrFlagEndpointNotFound
	case 200:
		var d struct {
			Data Flags `json:"data"`
		}

		if err := json.Unmarshal(b, &d); err != nil {
			return Flags{}, errors.Wrapf(err, "unmarshal response: %v", string(b))

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