hashicorp/nomad · error

rpc error: %w

Error message

rpc error: %w

What it means

ConnPool.RPC fails to establish an RPC client connection to a remote Nomad server and wraps the underlying error with "rpc error: %w". This is a transport-level failure in the connection pool's getRPCClient step (dial, handshake, or pool acquisition), not an application-level RPC error. The wrapped error (%w) contains the root cause.

Source

Thrown at helper/pool/pool.go:517

	s, err := conn.session.Open()
	if err != nil {
		return nil, fmt.Errorf("failed to open a streaming connection: %v", err)
	}

	if _, err := s.Write([]byte{byte(RpcStreaming)}); err != nil {
		conn.Close()
		return nil, err
	}

	return s, nil
}

// RPC is used to make an RPC call to a remote host
func (p *ConnPool) RPC(region string, addr net.Addr, method string, args interface{}, reply interface{}) error {
	// Get a usable client
	conn, sc, err := p.getRPCClient(region, addr)
	if err != nil {
		return fmt.Errorf("rpc error: %w", err)
	}
	defer conn.releaseUse()

	// Make the RPC call
	err = msgpackrpc.CallWithCodec(sc.codec, method, args, reply)
	if err != nil {
		sc.Close()

		// If we read EOF, the session is toast. Clear it and open a
		// new session next time
		// See https://github.com/hashicorp/consul/blob/v1.6.3/agent/pool/pool.go#L471-L477
		if helper.IsErrEOF(err) {
			p.clearConn(conn)
		}

		// If the error is an RPC Coded error
		// return the coded error without wrapping
		if structs.IsErrRPCCoded(err) {

View on GitHub (pinned to 482b49bf1a)

Solutions

1. Unwrap the error (%s of the cause) to identify whether it is dial failure, TLS, or timeout, and fix that root cause first
2. Verify the target server is up and listening on the RPC port (nomad server-members / netstat on 4647)
3. Check advertise_rpc / advertise addresses and firewall rules allow RPC between nodes
4. If TLS is enabled, verify ca_file, cert_file, key_file and verify_server_hostname consistency across the cluster

Example fix

// before
err := pool.RPC(region, addr, "Status.Ping", args, reply)
log.Printf("ping failed: %v", err)
// after
if err := pool.RPC(region, addr, "Status.Ping", args, reply); err != nil {
    var nerr net.Error
    if errors.As(err, &nerr) && nerr.Timeout() {
        log.Printf("RPC timeout to %s, retrying: %v", addr, err)
    } else {
        log.Printf("RPC transport failure to %s: %v", addr, err)
    }
}

conn, err := net.DialTimeout("tcp", addr.String(), 3*time.Second)
if err != nil {
    return fmt.Errorf("RPC endpoint %s unreachable before call: %w", addr, err)
}
conn.Close()

err := pool.RPC(region, addr, method, args, reply)
var nerr net.Error
if errors.As(err, &nerr) && (nerr.Timeout() || isTransient(nerr)) {
    return retryWithBackoff(call)
}
return err

When it happens

Trigger: Calling ConnPool.RPC (or Ping, serverWithNodeConn, maybeBootstrap, fetch which all route through RPC) when getRPCClient cannot obtain a usable client: target host unreachable, wrong port, TLS/mTLS misconfiguration, or pool connection establishment timeout.

Common situations: Server down or restarting during rolling upgrades; firewall blocking the RPC port (default 4647); advertise address misconfigured so peers dial a wrong IP; TLS certificate mismatch between client and server; DNS resolution failure in the region.

Related errors

• ack.Error
• No path to node
• error renewing the lease: %w
• Server at address %s failed ping: %v
• Region %q: %v

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/617b33e90990922f. Report an issue: GitHub.