ZeroMQ notes
Connect your code in any language, on any platform.
Looks like an embeddable networking library but acts like a concurrency framework.
ZeroMQ: an efficient, embeddable library that solves most of the problems an application needs to become nicely elastic across a network, without much cost.
Transports: in-process, inter-process, TCP and multicast.
Patterns: fan-out, pub-sub, task distribution, request-reply.
Patterns
Request - reply
Publish/subscribe
One way data distribution.
Server pushes updates to a set of clients.
A subscribed can set many subscriptions.
Parallel pipeline
Encoding/decoding messages
Protocol Buffers.
RabbitMQ
Acknowledgements vs publisher confirms
Acknowledgements: delivery processing acknowledgements from consumers to RabbitMQ.
Publisher confirms: broker acknowledgements to publishers.
Prefetch count
Prefetch count - max number of unacknowledged deliveries that are permitted on a channel.
Dead Letter Exchanges
Messages from a queue can be 'dead-lettered'; that is, republished to another exchange when rejected.
Terms
Slow joiner
Context
Context is a container for all sockets in single process and acts as as the transport for inproc sockets, which are the fastest way to connect threads in one process.
HWM (high-water mark)
Protects against memory overflows.
Server vs client
To create a connection between two nodes, you use zmq_bind() in one node and zmq_connect() in the other. As a general rule of thumb, the node that does zmq_bind() is a "server", sitting on a well-known network address, and the node which does zmq_connect() is a "client", with unknown or arbitrary network addresses. Thus we say that we "bind a socket to an endpoint" and "connect a socket to an endpoint", the endpoint being that well-known network address.