thanos-io/thanos · error

create Prometheus store

Error message

create Prometheus store

What it means

store.NewPrometheusStore failed to construct the Prometheus store proxy (StoreAPI served over gRPC). Construction validates the client and metadata functions; failures are wrapped as 'create Prometheus Store'. This happens before the gRPC server starts, so the sidecar exits.

Solutions

1. Correct the --prometheus.url flag value (include scheme, e.g. http://prometheus:9090)
2. Check earlier log lines for the underlying error detail; fix what NewPrometheusStore reports
3. Ensure you run a thanos version whose sidecar expects the current flag format
4. If running patched code, verify the promclient and metadata funcs passed to NewPrometheusStore are non-nil

Example fix

// before
--prometheus.url=prometheus.monitoring:9090   # no scheme
// after
--prometheus.url=http://prometheus.monitoring:9090

u, err := url.Parse(promURL)
if err != nil || (u.Scheme != "http" && u.Scheme != "https") {
    return fmt.Errorf("--prometheus.url must be an absolute http(s) URL, got %q", promURL)
}

promStore, err := store.NewPrometheusStore(...)
if err != nil {
    return errors.Wrap(err, "create Prometheus store")
}

When it happens

Trigger: errors.Wrap in runSidecar: NewPrometheusStore returned an error — e.g. an invalid --prometheus.url (unparseable/unsupported scheme) passed to the underlying HTTP client construction.

Common situations: Malformed --prometheus.url value (missing scheme, invalid characters); regression when wiring custom client functions; nil metadata functions from a failed earlier step in modified builds.

Understand the failure class

Background: "Invalid URL" / "URL cannot be empty": fix the malformed or missing URL behind request-construction failures — this error's family across 50 libraries.

Related errors

• create bucket compactor
• unable to load config file
• unable to create config reloader
• unable to load config initially
• tracing failed

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/a7944819b1af6a38. Report an issue: GitHub.

Appendix: source

Thrown at cmd/thanos/sidecar.go:320

	}

	// Setup the Reloader.
	{
		ctx, cancel := context.WithCancel(context.Background())
		g.Add(func() error {
			return reloader.Watch(ctx)
		}, func(error) {
			cancel()
		})
	}

	// Setup the gRPC server.
	{
		c := promclient.NewWithTracingClient(logger, httpClient, clientconfig.ThanosUserAgent)

		promStore, err := store.NewPrometheusStore(logger, reg, c, conf.prometheus.url, component.Sidecar, m.Labels, m.Timestamps, m.Version)
		if err != nil {
			return errors.Wrap(err, "create Prometheus store")
		}

		tlsCfg, err := tls.NewServerConfig(log.With(logger, "protocol", "gRPC"),
			conf.grpc.tlsSrvCert, conf.grpc.tlsSrvKey, conf.grpc.tlsSrvClientCA, conf.grpc.tlsMinVersion, conf.grpc.tlsCiphers, conf.grpc.tlsCurves)
		if err != nil {
			return errors.Wrap(err, "setup gRPC server")
		}

		exemplarSrv := exemplars.NewPrometheus(conf.prometheus.url, c, m.Labels)

		infoSrv := info.NewInfoServer(
			component.Sidecar.String(),
			info.WithLabelSetFunc(func() []labelpb.ZLabelSet {
				return promStore.LabelSet()
			}),
			info.WithStoreInfoFunc(func() (*infopb.StoreInfo, error) {
				if httpProbe.IsReady() {
					mint, maxt := m.Timestamps()

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