Log reguests from processes to remote clients through a zeromq-based broker.

When used in conjunction with MPI: Brokers running on non-compute nodes receive messages from compute-node MPI processes and dispatch such messages to remote clients.

Broker, client and logger services can be started in any order; if clients want to subscribe to messages from specific process ids then logger processes need to be started first to read the process id to be passed to clients.

Constraint:

• one subscription per remote process only; clients can receive data from multiple processes by using one socket per process; or they can receive data from all process at once. Subscription to a specific subset of processes is not supported; note that subscribing to more than a single process using a single socket with the current features implemented in zmq sockets it's not easy because only a simple match is performed; advanced (OR) filtering would have to be performed on the server side for this to work.

Flow:

• log source: publish to broker
• broker: subscribe to log sources; publish to clients
• client: subscribe to broker

The flow can be reversed to allow for communication from clients to servers to e.g. steer computation or select which data to log:

• compute process (usually same as log source): subscribe to control broker
• control broker: subscribe to control client; publish to compute process
• control client: publish to control broker

Use XPUB, XSUB sockets with zmq_proxy in the broker to allow subscriptions to be dispatched to remote publishers (log sources and compute processes).