apache/beam · error

error publishing message

Error message

error publishing message: %v

What it means

This error is returned by natsio's writer DoFn (ProcessElement) when jetstream.Js.PublishMsg fails to publish a message to a NATS JetStream subject. The NATS client returns an error (connection issues, subject problems, stream limits, etc.) and the DoFn wraps it with context so the pipeline element fails with a readable message. The original NATS error is included via %v.

Solutions

1. Verify NATS server connectivity and that the configured JetStream stream covers the target subject (nats stream info / add stream).
2. Check the wrapped %v cause: for max payload errors, reduce message size or raise server max_payload; for timeouts, increase publish timeout or check network.
3. Ensure the server has JetStream enabled (store_dir configured, --js flag on nats-server) if running a self-hosted server.
4. Add a dead-letter/retry pattern (e.g. a Sofa/beam combinator) so transient publish failures don't fail the whole bundle.
5. Confirm credentials/account limits allow publishing at the pipeline's throughput.

Example fix

// before: publishing to subject with no JetStream stream bound
js.PublishMsg(ctx, msg)
// error: error publishing message: nats: no responders available for request

// after: create/bind a stream for the subject first
// nats stream add ORDERS --subjects "orders.>"
// or via Go:
_, err := js.CreateStream(ctx, jetstream.StreamConfig{Name: "ORDERS", Subjects: []string{"orders.>"}})

// Before running the pipeline, verify JetStream connectivity and stream coverage for the subject:
conn, err := nats.Connect(url)
if err != nil { return err }
js, _ := jetstream.New(conn)
if _, err := js.StreamNameForSubject(ctx, subject); err != nil {
    return fmt.Errorf("no stream bound to subject %s: %w", subject, err)
}

When it happens

Trigger: Calling beam.Par with the natsio.Write transform when the underlying jetstream PublishMsg call fails: NATS server unreachable, subject has no stream binding, JetStream publish timeouts, max payload exceeded, or stream limits (max msgs/bytes) reached.

Common situations: NATS server restarted or down mid-pipeline; publishing to a subject not covered by any JetStream stream; message larger than max_payload; exceeding stream retention/storage limits; using a JetStream-enabled write against a core-NATS-only server.

Related errors

• err
• error fetching messages
• chunk send failed
• could not create data operations client
• end sequence number must be greater than 0

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/76e320eafa42fb3b. Report an issue: GitHub.

Appendix: source

Thrown at sdks/go/pkg/beam/io/natsio/write.go:101

func (fn *writeFn) ProcessElement(
	ctx context.Context,
	elem ProducerMessage,
	emit func(PublishAck),
) error {
	msg := &nats.Msg{
		Subject: elem.Subject,
		Data:    elem.Data,
		Header:  elem.Headers,
	}

	var opts []jetstream.PublishOpt
	if elem.ID != "" {
		opts = append(opts, jetstream.WithMsgID(elem.ID))
	}

	ack, err := fn.js.PublishMsg(ctx, msg, opts...)
	if err != nil {
		return fmt.Errorf("error publishing message: %v", err)
	}

	pubAck := PublishAck{
		Stream:    ack.Stream,
		Subject:   elem.Subject,
		ID:        elem.ID,
		Sequence:  ack.Sequence,
		Duplicate: ack.Duplicate,
	}
	emit(pubAck)

	return nil
}

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