ZeroMQ architecture for cache-like service

Question

I made a service which accepts requests on a 0MQ router socket in NetMQ, and acts mostly like a cache for other apps, i.e. it can receive a "GET" request and send a response, or it can receive a "PUT" request which doesn't need a response.

I have two issues though:

1. I tried using a RequestSocket in client code, but it still fails if I don't wait for a response after a sent message (I guess this is how REQ/REP works in 0MQ). What is the appropriate 0MQ socket type if I only want to get a response for some message types?

2. Currently my client code creates a new RequestSocket instance whenever it needs to communicate with the service. Is there a thread-safe way in NetMQ where I could have a single socket that can be reused over the client code when I need to send a request and get a response, without the need to create a new connection each time?

The service code is currently basically:

var socket = new RouterSocket(endpoint);
socket.ReceiveReady += (sender, e) =>
{
    var msg = e.Socket.ReceiveMultipartMessage();
    var action = msg[3].ConvertToString();
    switch (action)
    {
        case "GET":
        {
            var key = msg[4].ConvertToString();
            var data = _cache.Get(key);
            var response = new NetMQMessage();
            response.Append(msg[0]); // msg id
            response.Append(NetMQFrame.Empty);
            response.Append(msg[4]);
            response.Append(data);
            e.Socket.SendMultipartMessage(response);
        }
        break;

        case "SET":
        {
            var key = msg[4].ConvertToString();
            var data = msg[5].Buffer;
            _cache.Set(key, data);

            // no response needed here, but needed for RequestSocket clients                
        }
        break;

        default: throw new NotImplementedException();
    }
};