no gRPC connection, you must call connect first

Error message

no gRPC connection, you must call connect first

What it means

Every client.invoke(method, request) goes through buildInvokeRequest, which first verifies a VU state exists and then that c.conn is set. c.conn is only assigned by a successful client.connect(), so invoking before connecting - or after connect failed - produces this error before the method name is even looked at.

Solutions

Call client.connect(addr, params) before invoke - it is blocking (no await needed) and returns true on success: const ok = client.connect(addr); if (!ok) throw new Error('connect failed').
Do the connection once per VU or in setup and guard the invoke path on the connect result.
If connect is conditional, initialize a flag (let connected = false) and check it before invoking.

Example fix

// before
export default function () {
  client.invoke('hello.HelloService/SayHello', { name: 'k6' }); // throws: no gRPC connection
}

// after
export default function () {
  client.connect('grpcbin.k6.io:443');
  client.invoke('hello.HelloService/SayHello', { name: 'k6' });
}

Defensive patterns

Strategy: validation

Validate before calling

// connect() is blocking and returns a boolean - assert it before invoking
const connected = client.connect('grpcbin.k6.io:443');
if (!connected) {
  throw new Error(`failed to connect to gRPC server`);
}
client.invoke('hello.HelloService/SayHello', { name: 'k6' });

Try / catch

try {
  client.invoke(method, req);
} catch (e) {
  if (/must call connect first/.test(e.message)) {
    throw new Error('gRPC client not connected - call client.connect() before invoke()');
  }
  throw e;
}

Prevention

Connect once per VU (or in setup) and store the result in a module-level flag.
Never swallow connect() exceptions - a silent failure leaves conn nil and every invoke broken.
Order boilerplate as: load (init) -> connect (setup/VU) -> invoke.

When it happens

Trigger: client.invoke('pkg.Service/Method', req) called before any client.connect(addr); calling invoke when connect() threw and the script swallowed the error with try/catch and continued; or forgetting that connect must complete first in each VU/setup that invokes.

Common situations: Copy-pasting invoke examples while deleting the connect boilerplate; conditional connect logic (if (needsTls) connect()) that skips the call on one branch; error-handling around connect that logs and proceeds, leaving conn nil.

Related errors

AI-assisted analysis of grafana/k6@8d06114777 (2026-08-18). Data as JSON: /api/errors/a5afdb5d227bcd33. Report an issue: GitHub.

Appendix: source

Thrown at internal/js/modules/k6/grpc/client.go:387

	}()

	return promise, nil
}

// buildInvokeRequest creates a new InvokeRequest from the given method name, request object and parameters
func (c *Client) buildInvokeRequest(
	method string,
	req sobek.Value,
	params sobek.Value,
) (grpcext.InvokeRequest, error) {
	grpcReq := grpcext.InvokeRequest{}

	state := c.vu.State()
	if state == nil {
		return grpcReq, common.NewInitContextError("invoking RPC methods in the init context is not supported")
	}
	if c.conn == nil {
		return grpcReq, errors.New("no gRPC connection, you must call connect first")
	}
	if method == "" {
		return grpcReq, errors.New("method to invoke cannot be empty")
	}
	if method[0] != '/' {
		method = "/" + method
	}
	methodDesc := c.mds[method]
	if methodDesc == nil {
		return grpcReq, fmt.Errorf("method %q not found in file descriptors", method)
	}

	p, err := newCallParams(c.vu, params)
	if err != nil {
		return grpcReq, fmt.Errorf("invalid GRPC's client.invoke() parameters: %w", err)
	}

	// k6 GRPC Invoke's default timeout is 2 minutes

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