thanos-io/thanos · error

unable to create request

Error message

unable to create request

What it means

After building the URL (base + /api/v1/read), startPromRemoteRead creates the POST http.Request via http.NewRequest. If the URL is invalid or malformed, the wrapped error "unable to create request" is returned. This almost always means the store's configured base address is not a valid absolute HTTP URL.

Solutions

1. Fix the store's base address to be a full absolute URL including scheme (http://host:9090)
2. Validate the address at store-creation time with url.Parse before issuing queries
3. Check config files/env vars feeding the address for empty or malformed values
4. Verify path joining does not produce an invalid URL when the base path is unusual

Example fix

// before
address: "prometheus:9090"
// after
address: "http://prometheus:9090"

u, err := url.Parse(addr)
if err != nil || u.Scheme == "" || u.Host == "" {
    return fmt.Errorf("invalid store address %q: need absolute URL with scheme", addr)
}

resp, err := store.Series(ctx, req)
if err != nil && strings.Contains(err.Error(), "unable to create request") {
    // address malformed: fix --store-address / config and re-create the store
}

When it happens

Trigger: Constructing a PrometheusStore with --store-address / base URL that is empty, missing scheme (e.g. "prometheus:9090" instead of "http://prometheus:9090"), or contains characters http.NewRequest rejects (spaces, control chars).

Common situations: Typo in store address flag; missing http:// scheme prefix in static config or file_sd targets; environment interpolation producing an empty address; invalid characters from templated addresses.

Understand the failure class

Background: "Invalid URL" errors: why new URL(), URI.parse, and reqwest::Url reject your string — missing scheme, whitespace, and bad path format — this error's family across 39 libraries.

Related errors

• is 'web.enable-admin-api' flag enabled? got non-200…
• creating request to downstream URL
• failed to create matchers cache
• failed to validate prometheus flags
• failed to get prometheus version

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/85fea78978a07d5f. Report an issue: GitHub.

Appendix: source

Thrown at pkg/store/prometheus.go:472

	return chks, nil
}

func (p *PrometheusStore) startPromRemoteRead(ctx context.Context, q *prompb.Query) (presp *http.Response, err error) {
	reqb, err := proto.Marshal(&prompb.ReadRequest{
		Queries:               []*prompb.Query{q},
		AcceptedResponseTypes: p.remoteReadAcceptableResponses,
	})
	if err != nil {
		return nil, errors.Wrap(err, "marshal read request")
	}

	u := *p.base
	u.Path = path.Join(u.Path, "api/v1/read")

	preq, err := http.NewRequest("POST", u.String(), bytes.NewReader(snappy.Encode(nil, reqb)))
	if err != nil {
		return nil, errors.Wrap(err, "unable to create request")
	}
	preq.Header.Add("Content-Encoding", "snappy")
	preq.Header.Set("Content-Type", "application/x-stream-protobuf")
	preq.Header.Set("X-Prometheus-Remote-Read-Version", "0.1.0")

	preq.Header.Set("User-Agent", clientconfig.ThanosUserAgent)
	presp, err = p.client.Do(preq.WithContext(ctx))
	if err != nil {
		return nil, errors.Wrap(err, "send request")
	}
	if presp.StatusCode/100 != 2 {
		// Best effort read.
		b, err := io.ReadAll(presp.Body)
		if err != nil {
			level.Error(p.logger).Log("msg", "failed to read response from non 2XX remote read request", "err", err)
		}
		_ = presp.Body.Close()
		return nil, errors.Errorf("request failed with code %s; msg %s", presp.Status, string(b))

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