Running multiple MONICAs on High Performance Computers (Clusters)

This section explains how to run multiple MONICA simulations on a High-Performance Computing (HPC) cluster or across multiple machines. MONICA can be launched in server mode, allowing it to receive simulation jobs via ZeroMQ and run them in parallel.

1. Introduction

When running MONICA on HPC systems or clusters, you can start MONICA in server mode using the command:

monica-zmq-server

In this mode, MONICA acts as a server process that listens for incoming simulation requests sent through ZeroMQ sockets. Each message contains the full configuration for one simulation run.

This setup allows distributed simulations across:

Multiple CPU cores on the same node,
Multiple nodes within a cluster,
Or even different machines connected via a network

2. Basic Command Usage

You can view available options with:

monica-zmq-server -h

or

monica-zmq-server --help

This will display all supported flags and their default values.

3. Command Syntax

monica-zmq-server [options]

Example (default single-node configuration):

monica-zmq-server --serve-address tcp://*:6666 --output-address tcp://*:7777

4. Available Options

Overview of all configuration option.

Option	Long Form	Description	Default Value
`-h`	`--help`	Show help output and exit.	—
`-v`	`--version`	Print MONICA and ZeroMQ version info.	—
`-d`	`--debug`	Enable detailed debug output for troubleshooting.	—
`-s`	`--serve-address`	Bind the MONICA server to a specific address (used for direct client connections).	`tcp://*:6666`
`-p`	`--proxy-address`	Connect to one or more proxy addresses for receiving work. Multiple addresses can be comma-separated.	`tcp://localhost:6666`
`-bi`	`--bind-input`	Bind the input port manually (for use when controlling binding explicitly).	—
`-ci`	`--connect-input`	Connect the input port (default mode).	(default)
`-i`	`--input-address`	Specify one or more input addresses for receiving simulation jobs (comma-separated).	`tcp://localhost:6666`
`-bo`	`--bind-output`	Bind the output port manually (for explicit output binding).	—
`-co`	`--connect-output`	Connect the output port (default mode).	(default)
`-o`	`--output-address`	Set output address(es) for sending results to clients or proxies.	`tcp://localhost:7777`
`-or`	`--router-output-address`	Send results using a router socket instead of the default dealer socket.	`tcp://localhost:7777`
`-c`	`--control-address`	Address for MONICA’s control interface (used for starting, stopping, or monitoring processes).	`tcp://localhost:8888`

5. Example Configurations

Example 1 – Basic Local Setup

Run MONICA on a single machine, serving jobs locally:

monica-zmq-server --serve-address tcp://*:6666 --output-address tcp://*:7777

Clients (or scripts) can then send simulation requests to port 6666 and receive results from port 7777.

Example 2 – Connecting via Proxy

If you already have a MONICA proxy running (for example via Docker or Singularity), then connect MONICA server to it:

monica-zmq-server --proxy-address tcp://proxy-hostname:6666 --output-address tcp://proxy-hostname:7777

This allows the MONICA instance to communicate through the proxy layer, distributing workloads across multiple workers.

Example 3 –Cluster Node Setup

To use MONICA across several nodes (each node runs as a worker connected to a proxy):

Run the proxy on the master node (see the Singularity or Docker setup).
Start MONICA worker processes on each compute node, connecting them to the proxy:

monica-zmq-server --proxy-address tcp://<proxy-node>:6666 --output-address tcp://<proxy-node>:7777

3. Monitor performance via logs or the control port (default: 8888).

Notes:

Use different ports if multiple MONICA servers are running on the same host.
For distributed runs, make sure all machines can communicate via TCP on the specified ports.
The control port (8888) can be used for remote process management and monitoring.
On HPC systems, you can manage MONICA processes via job schedulers like SLURM or PBS using scripts similar to the Singularity examples.