Modbus TCP proxy

Many modbus devices support only one or very few clients. This proxy acts as a bridge between the client and the modbus device. It can be seen as a layer 7 reverse proxy. This allows multiple clients to communicate with the same modbus device.

When multiple clients are connected, cross messages are avoided by serializing communication on a first come first served REQ/REP basis.

This project is the Rust version of the Python based modbus-proxy project.

I did it because it fitted my personal goal of exercising with the Rust programming language and it's async based tokio library.

The goal was to produce a robust, highly concurrent server with a low memory footprint.

Installation

$ cargo install modbus-proxy-rs

Running the server

First, you will need write a configuration file where you specify for each modbus device you which to control:

• modbus connection (the modbus device url)
• listen interface (to which url your clients should connect)

Configuration files can be written in YAML (.yml or .yaml) or TOML (.toml).

Suppose you have a PLC modbus device listening on plc1.acme.org:502 and you want your clients to connect to your machine on port 9000. A YAML configuration would look like this:

devices:
- modbus:
    url: plc1.acme.org:502     # device url (mandatory)
  listen:
    bind: 0:9000               # listening address (mandatory)

Assuming you saved this file as modbus-config.yml, start the server with:

$ modbus-proxy-rs -c ./modbus-config.yml

Now, instead of connecting your client(s) to plc1.acme.org:502 you just need to tell them to connect to *machine*:9000 (where machine is the host where modbus-proxy is running).

Note that the server is capable of handling multiple modbus devices. Here is a configuration example for 2 devices:

devices:
- modbus:
    url: plc1.acme.org:502
  listen:
    bind: 0:9000
- modbus:
    url: plc2.acme.org:502
  listen:
    bind: 0:9001

Logging

Log levels can be adjusted by setting the RUST_LOG environment variable (default is warn):

$ RUST_LOG=debug modbus-proxy-rs -c ./modbus-config.yml

Docker

This project ships with a Dockerfile which you can use as a base to launch modbus-proxy inside a docker container.

First, build the docker image with:

$ docker build -t modbus-proxy .

Assuming you have prepared a config.yml in the current directory:

devices:
- modbus:
    url: plc1.acme.org:502
  listen:
    bind: 0:502

The supplied docker image by default runs the command /modbus-proxy-rs -c /etc/modbus-proxy.yml. Therefore, running launching a container is as simple as:

docker run --init --rm -p 5020:502 -v $PWD/config.yml:/etc/modbus-proxy.yml modbus-proxy

You can supply a different configuration path (ex: /config.yml):

docker run --init --rm -p 5020:502 -v $PWD/config.yml:/config.yml modbus-proxy -c /config.yml

Now you should be able to access your modbus device through the modbus-proxy by connecting your client(s) to <your-hostname/ip>:5020.

Note that for each modbus device you add in the configuration file you need to publish the corresponding bind port on the host (-p <host port>:<container port> argument).

Credits

Development Lead

• Tiago Coutinho coutinhotiago@gmail.com

Contributors

None yet. Why not be the first?