Chapter 6. Network connections

Connection URLs encode the information used to establish new connections.

scheme://host[:port]

amqps://example.com
amqps://example.net:56720
amqp://127.0.0.1
amqp://[::1]:2000

To connect to a remote server, call the Container.connect() method with a connection URL. This is typically done inside the MessagingHandler.on_start() method.

class ExampleHandler(MessagingHandler):
    def on_start(self, event):
        event.container.connect("amqp://example.com")

    def on_connection_opened(self, event):
        print("Connection", event.connection, "is open")

For information about creating secure connections, see Chapter 7, Security.

Reconnect allows a client to recover from lost connections. It is used to ensure that the components in a distributed system reestablish communication after temporary network or component failures.

AMQ Python enables reconnect by default. If a connection is lost or a connection attempt fails, the client will try again after a brief delay. The delay increases exponentially for each new attempt, up to a default maximum of 10 seconds.

To disable reconnect, set the reconnect connection option to False.

container.connect("amqp://example.com", reconnect=False)

To control the delays between connection attempts, define a class implementing the reset() and next() methods and set the reconnect connection option to an instance of that class.

class ExampleReconnect(object):
    def __init__(self):
        self.delay = 0

    def reset(self):
        self.delay = 0

    def next(self):
        if self.delay == 0:
            self.delay = 0.1
        else:
            self.delay = min(10, 2 * self.delay)

        return self.delay

container.connect("amqp://example.com", reconnect=ExampleReconnect())

The next method returns the next delay in seconds. The reset method is called once before the reconnect process begins.

AMQ Python allows you to configure multiple connection endpoints. If connecting to one fails, the client attempts to connect to the next in the list. If the list is exhausted, the process starts over.

To specify multiple connection endpoints, set the urls connection option to a list of connection URLs.

urls = ["amqp://alpha.example.com", "amqp://beta.example.com"]
container.connect(urls=urls)

It is an error to use the url and urls options at the same time.

AMQ Python can accept inbound network connections, enabling you to build custom messaging servers.

To start listening for connections, use the Container.listen() method with a URL containing the local host address and port to listen on.

class ExampleHandler(MessagingHandler):
    def on_start(self, event):
        event.container.listen("0.0.0.0")

    def on_connection_opened(self, event):
        print("New incoming connection", event.connection)

The special IP address 0.0.0.0 listens on all available IPv4 interfaces. To listen on all IPv6 interfaces, use [::0].

For more information, see the server receive.py example.