On our last packaging line upgrade in October, I used Node-RED 4.0 with OPC UA and MQTT to simulate I/O and exercise PLC sequences, cutting FAT time by about 30%. I can share the flow and a lightweight Grafana dashboard template; what other free simulators (OPC UA server, Modbus TCP) have you found reliable on a laptop without admin rights?
Admin lock-downs drive me nuts — “no admin rights” is my life too. For OPC UA, I’ve had good luck running the node-opcua sample server via npx node-opcua-sample-server (no install if Node.js is there) — GitHub - node-opcua/node-opcua: Unlocking the Full Potential of OPC UA with Typescript and NodeJS - http://node-opcua.github.io/; for Modbus TCP, ModbusPal’s.jar is portable and steady. Since you’re already on Node-RED 4.0, you can keep it all in one flow with node-opcua/modbus nodes; do you need security or just anonymous for FAT?
In your Node-RED 4.0 setup, drop in the node-red-contrib-opcua Flex Server to spin up a local UA server inside the flow — no admin, and you can map the same simulated I/O you’re already driving. For Modbus TCP, diagslave is my go‑to portable exe (Free Modbus Slave Simulator and Test Tool); it’s rock solid but CLI‑only, which is a bit when you’re tweaking coils on the fly. Do you need certs/user tokens on the UA side, or is anonymous fine for FAT?
But modbusPal worked well here — portable jar, no admin; for UA, freeopcua demo server via user-space pip: http://modbuspal.sourceforge.net/.
Quick win: Eclipse Milo’s demo server runs from a zip with just Java — no install — and is stable enough to drive sequence checks; the example JAR is here: https://github.com/eclipse/milo/tree/master/examples/server. @hcorbin76 have you tried that route, or do you stick to jars only? For Modbus TCP, I keep WinPython in my user folder and spin up a pymodbus TCP server so I can script states, which pairs nicely with your October Grafana template.