Majordomo Management Interface

// under zeromq distributed systems

In my last post, we saw an example of the majordomo protocol (MDP) in action. MDP is a reliable service oriented protocol. It can be become the single point to server different services to any user. The broker implementation in the example also has a special feature, called the majordomo management interface (MMI), it can tell if there is at least on worker for a given service, i.e., if the the service is available or not. This is achieved by creating a mmi.service service on the broker. The service can be easily called by:

reply = client.send(b"mmi.service", b"s_name")

This will check if the service s_name is available or not. The reply will be 200 if s_name is available otherwise it will return 404.

Let use look at the sections of the mdbroker.py that enables us to do so. There is an attribute INTERNAL_SERVICE_PREFIX = b"mmi." this determines the prefix by which the request must start. The function process_client shown below check if the requested service is the management interface.

def process_client(self, sender, msg):
        """Process a request coming from a client."""
        assert len(msg) >= 2 # Service name + body
        service = msg.pop(0)
        # Set reply return address to client sender
        msg = [sender, b''] + msg
        if service.startswith(self.INTERNAL_SERVICE_PREFIX):
            self.service_internal(service, msg)
        else:
            self.dispatch(self.require_service(service), msg)

If the management interface is requested then the service_internal function is called:

def service_internal(self, service, msg):
        """Handle internal service according to 8/MMI specification"""
        returncode = b"501"
        if b"mmi.service" == service:
            name = msg[-1]
            returncode = b"200" if name in self.services else b"404"
        msg[-1] = returncode

        # insert the protocol header and service name after the routing envelope ([client, ''])
        msg = msg[:2] + [MDP.C_CLIENT, service] + msg[2:]
        self.socket.send_multipart(msg)

This only returns if a service is present or not. It still does not give us an entire list of services available. We can do that by making a little modification to the code.

def service_internal(self, service, msg):
        """Handle internal service according to 8/MMI specification"""
        returncode = b"501"
        if b"mmi.service" == service:
            returnnode = b", ".join(self.services)
        msg[-1] = returncode

        # insert the protocol header and service name after the routing envelope ([client, ''])
        msg = msg[:2] + [MDP.C_CLIENT, service] + msg[2:]
        self.socket.send_multipart(msg)

Go Top

shishir pandey

Published

Majordomo Management Interface