Deploying OpenPLC

Overview

OpenPLC is an open-source, IEC 61131-3 compliant soft PLC: you write ladder logic or structured text in the OpenPLC Editor, upload it through the runtime’s web interface, and the runtime executes it and exposes I/O over Modbus TCP. Running it as a container on an ALPON X5 AI or ALPON X4 turns the device into a network-attached controller that stays manageable through ALPON Cloud.

This guide builds an arm64 OpenPLC runtime image, pushes it to the Sixfab Container Registry, and deploys it on the device. The example targets the OpenPLC web interface and Modbus TCP; add a hardware layer only after reviewing its device-access and privilege requirements. The steps below are identical on ALPON X4 and ALPON X5 AI.

Project file structure

Your OpenPLC containerized application has the following file structure:

openplc_project/
├─── hardware_layers/
├──── .donotdelete
├─── entrypoint.sh
└─── Dockerfile

1. 1

   Create a reviewable ARM64 Dockerfile

   Do not bake SSH into the container

   The previous version of this guide enabled SSH with a fixed root:root password and added end-of-life Debian Buster repositories with apt-key. Do not use that pattern. A container does not need an SSH daemon: use ALPON Cloud Shell for application access and the device Remote Terminal for host diagnostics.

   Pin the OpenPLC source to a reviewed release tag or commit when building. The example below intentionally requires OPENPLC_REF; replacing it with an unpinned branch would make later builds non-reproducible. Save it as Dockerfile in openplc_project/:

   Dockerfile dockerfile

   FROM debian:bookworm-slim
   
   ARG OPENPLC_REF
   
   RUN test -n "$OPENPLC_REF" \\
       && apt-get update \\
       && apt-get install -y --no-install-recommends \\
          ca-certificates git build-essential autoconf automake \\
          bison flex cmake libtool pkg-config python3 python3-pip \\
       && rm -rf /var/lib/apt/lists/*
   
   RUN git clone https://github.com/thiagoralves/OpenPLC_v3.git /OpenPLC_v3 \\
       && cd /OpenPLC_v3 \\
       && git checkout "$OPENPLC_REF" \\
       && ./install.sh docker
   
   # Add only hardware layers you have reviewed and need.
   
   COPY ./hardware_layers/ /OpenPLC_v3/webserver/core/hardware_layers/
   COPY ./entrypoint.sh /usr/local/bin/openplc-entrypoint
   RUN chmod 0755 /usr/local/bin/openplc-entrypoint
   
   EXPOSE 8080 502
   STOPSIGNAL SIGTERM
   ENTRYPOINT ["/usr/local/bin/openplc-entrypoint"]

2. 2

   Create the entrypoint

   The entrypoint starts OpenPLC without an SSH daemon or embedded password. It also forwards termination to the runtime when the container is stopped. Save it as entrypoint.sh next to the Dockerfile:

   entrypoint.sh sh

   #!/bin/sh
   set -eu
   
   cd /OpenPLC_v3
   
   stop_openplc() {
     if [ -x ./stop_openplc.sh ]; then
       ./stop_openplc.sh || true
     fi
     exit 0
   }
   
   trap stop_openplc INT TERM
   
   ./start_openplc.sh
   
   # OpenPLC starts its services in the background; keep PID 1 available
   # to receive the stop signal from the container runtime.
   while :; do
     sleep 3600 &
     wait $!
   done

   Use the web interface on port 8080 for OpenPLC administration. Do not expose an SSH port from the container.

3. 3

   Build and push the OpenPLC image

   Build the image for arm64 and pass the reviewed OpenPLC tag or commit. On an x86 Linux build host, register ARM emulation first as described in Deploy Applications.

   bash · build the image

   docker buildx build --load --platform linux/arm64 \\
     --build-arg OPENPLC_REF=<reviewed-tag-or-commit> \\
     -t openplc-container:<version> .

   Then log in to Sixfab Registry, click + Add Container, and follow the prompts to push the image.

   Pushing images to the Sixfab Container Registry

   For the full walkthrough of tagging and pushing an image, see Update Containers from the Sixfab Container Registry.

4. 4

   Deploy the container on ALPON

   Once the image is in the Sixfab Container Registry, open your device in ALPON Cloud, go to the Applications section, and click + Deploy. In the Deploy Container window, use these settings:

   Container Name The application name, e.g. openplc-application.

   Image The OpenPLC image and tag you pushed to the Sixfab Container Registry.

   Ports Click + Add More and add the port mappings in the table below.

   Hardware access Optional — only for a reviewed GPIO hardware layer; see the callout below. Leave Privileged off for a Modbus TCP-only deployment.

   From	To	Purpose
   30880	8080	OpenPLC web interface
   30502	502	Modbus TCP, only when required by the deployment

   Hardware access (optional)

   For a reviewed GPIO hardware layer, add a Read/Write bind mount from /dev/gpiomem to /dev/gpiomem in the Volumes section and enable Privileged mode. Do not enable Privileged mode for a Modbus TCP-only deployment. The ALPON GPIO Add-on 5 V rail must also be enabled through GPIO 21; see Access GPIO, Push Buttons, and USB from Containers.

   

   Click + Deploy to launch OpenPLC on the device.

5. 5

   Open the OpenPLC web interface

   Once the deployment finishes, find the device's local IP address under Asset Details → Network tab → Interface Monitoring → Details, then open the web interface in a browser:

   browser · OpenPLC web interface

   http://<DEVICE_IP>:30880

   The OpenPLC login page should load. If it doesn't, double-check the Dockerfile, verify your registry credentials, confirm the container is running in the Applications section, and ensure any device access the hardware layer needs was granted in step 4.

The Deploy Container window in ALPON Cloud with the OpenPLC image and port mappings configured.