Network.Mom.Stompl.Patterns.Balancer

This module provides a balancer for services and tasks and a topic router. Balancers for services and tasks improve scalability and reliability of servers and workers. Workers should always be used with a balancer (since balancing workload is the main idea of workers); servers can very well be used without a balancer, but won't scale with increasing numbers of clients.

A balancer consists of a registry to which servers and workers connect; servers and workers are maintained in lists according to the job they provide. Clients and pushers send requests to the balancer, which then forwards the request to a server or worker. The client will receive the reply not through the balancer, but directly from the server (to which the reply queue was forwarded as part of the request message -- see ClientA for details).

With servers and workers sending heartbeats, a balancer also improves reliability in contrast to a topology where a task is pushed to a single worker or a request is sent to only one server.

A router is a forwarder of a topic. A router is very similar to a publisher (PubA) with the difference that the router does not create new topic data, but uses topic data received from a publisher (a router, hence, is a subscriber and a publisher). Routers can be used to balance the workload of publishers: Instead of one publisher serving thousands of subscribers, the initial publisher would serve thousands of routers, which, in their turn, serve thousands of subscribers (or even other routers).

Balancer

withBalancer :: Con -> String -> QName -> (Int, Int) -> QName -> OnError -> IO r -> IO r

Create a Service and Task Balancer with the lifetime of the application-defined action passed in and start it in a background thread:

• Con: Connection to a Stomp broker;
• String: Name of the balancer, used for error handling;
• QName: Registration queue -- this queue is used by providers to connect to the registry, it is not used for consumer requests;
• (Int, Int): Heartbeat range of the Registry (see withRegistry for details);
• QName: Request queue -- this queue is used for consumer requests;
• OnError: Error handling;
• IO r: Action that defines the lifetime of the balancer; the result r is also the result of withBalancer.

Router

withRouter :: Con -> String -> JobName -> QName -> QName -> QName -> Int -> OnError -> IO r -> IO r

Create a router with the lifetime of the application-defined action passed in and start it in a background thread:

• Con: Connection to a Stomp broker;
• String: Name of the router, used for error handling;
• JobName: Routed topic;
• QName: Registration queue of the source publisher;
• QName: Queue through which the internal subscriber will receive the topic data from the source publisher;
• QName: Registration queue of the target publisher to which subscribers will connect;
• Int: Registration timeout (timeout to register at the source publisher);
• QName: Request queue -- this queue is used for consumer requests;
• OnError: Error handling;
• IO r: Action that defines the lifetime of the router; the result r is also the result of withRouter.