The PLC4X OPC UA server integration is based around the Eclipse Milo OPC UA server. It uses PLC4X to communicate with industrial devices effectively acting as a industrial OPC UA gateway.

Building the server

The OPC UA server can be built using maven as part of the PLC4X build.

mvn install

This creates a target directory within plc4x/plc4j/integrations/opcua-server containing a jar file which is the main java executable.

Configuration File

The config.yml file is used to configure the server. The following root level settings should be configured.

  • version: The version is just an internal check to confirm that the right version of the configuration file is being used.

  • dir: This is the directory to the security directory. This is where all configuration is stored including certificates. Be sure to secure this directory with the correct permissions.

  • name: This is the name of the OPC UA server. It can be anything but shouldn’t contain spaces.

  • disableInsecureEndpoint: This is used to disable the remote insecure OPC UA endpoint.

  • tcpPort: this can be used to change the opc.tcp port.

  • httpPort: this can be used to change the http.tcp port.

  • devices: is a list of PLC’s or devices that the server should communicate with. Each device should include a name:, connectionString:, and a list of tags:.

For each device within devices the following settings should be configured.

  • name: This is the name of the device. It can anything as long as it doesn’t contain spaces.

  • connectionString: Can be any valid PLC4X connection string.

For each tag with tags the following settings should be configured:-

  • alias: This is the name of tag it can be anything but shouldn’t have spaces. This will be shown as the tag name within the OPC UA server tree. Be sure that this is unique within the configuration file.

  • address: This is any valid PLC4X address that matches the connection type.

An example configuration file is shown below.

version: "0.8"
dir: {path-to-security-dir}
name: "Plc4xOPCUAServer"
disableInsecureEndpoint: true
    - name: "ModbusDevice"
      connectionString: "modbus-tcp://"
        - alias: "TemporaryBOOLARRAY"
          address: "000001:BOOL[10]"
        - alias: "TemporaryWORD2"
          address: "400002:WORD"
        - alias: "TemporaryUINT3"
          address: "400003:UINT"
        - alias: "TemporaryINT4"
          address: "400004:INT"
        - alias: "TemporaryDINT5"
          address: "400005:DINT[4]"
        - alias: "TemporaryREAL6"
          address: "400006:REAL"
        - alias: "TemporaryREAL7"
          address: "400007:REAL"
        - alias: "TemporaryREAL8"
          address: "400008:REAL"
- name: "SimulationDevice"
    connectionString: "simulated://"
        - alias: "Temporary"
          address: "RANDOM/Temporary:Integer"
tcpPort: 12687
httpPort: 8445


To run the java executable execute:-

java -jar plc4x-opcua-server-0.8.0-uber-jar.jar -c {path-to-config-file} -i

This will start the OPC UA server with the interactive switch (-i). This prompts the server to ask for usernames and passwords upon startup. However, during normal operation the -i switch should be left out.

If a certificate isn’t available at {path-to-security-dir}/security/plc4x-opcuaserver.pfx then a self signed is created. This certificate is password protected with the security password given during startup.

If you place another certificate here make sure it is password protected and set the password by running the server again with --set-password switch.

java -jar plc4x-opcua-server-0.8.0-uber-jar.jar -c {path-to-config-file} -i -s

Once the OPC UA server is running you are able to connect to it from your favorite OPC UA client using the connection string.


Replacing the {ip.address} with the servers IP address.

If you want to use an encrypted connection be sure to move the client certificate created in {path-to-security-dir}/security/pki/rejected to the trusted directory. Otherwise the client will receive a security error when trying to connect.