How to Connect to an OPC UA Server


This guide is to help you connect to an OPC UA server, using Connectware. It assumes that you understand the fundamental Connectware concepts. For that you can check out the Technical Overview. To follow the example, you should have a Connectware instance running. If you don’t have that, learn Installing Cybus Connectware. Although we focus on OPC UA here, you should also be familiar with MQTT. If in doubt, head over to MQTT Basics.


You will learn to integrate OPC UA servers into your Connectware use case. Everything you need to get started will be covered in the following topics:

  1. Browsing the OPC UA address space
  2. Identifying OPC UA datapoints
  3. Mapping OPC UA data to MQTT
  4. Verifying data in the Connectware Explorer

Service YAMLs used in this lesson are available on GitHub.

Selecting the Tools

OPC UA Server

Our example utilizes the OPC UA server at, because it is publicly available. You can of course bring your own device instead.

OPC UA Browser

This guide recommends using FreeOpcUa’s Simple OPC UA GUI client for exploration. It is open source and offers convenient installation on Windows, Linux and Mac. If you prefer working on the terminal, go for Etienne Rossignon’s opcua-commander. If you have another option available, you may as well stick to it.

Exploring the OPC UA Address Space

Let’s get started! Launch your OPC UA browser and connect to the endpoint opc.tcp:// (or whatever endpoint applies to the device you brought). Tada! – the three root nodes Objects, Types, and Views should show up.

OPC UA Server Connection Established

Selecting Datasource Nodes

Explore and find the node which is displayed as CurrentTime. Select it and take a look at the Attributes pane – according to the NodeClass attribute we are dealing with a Variable which, by specification, contains a Value attribute. Variable nodes allow us to read and write data, depending on the AccessLevel attribute.

Right click on CurrentTime and select subscribe to data change. The Subscriptions pane then shows the actual value and it is updating at a fast rate.

OPC UA Server browse current time

Now we know that Variable nodes in the OPC UA address space are the datasources, but how to make use of them with Connectware? There are two ways to reference them:

  1. By NodeId, which is a node’s unique identifier. For example, the CurrentTime variable’s NodeId is i=2258.
  2. By BrowsePath, which is the path of BrowseName when you navigate the treeview. For example, the CurrentTime variable’s BrowsePath assembles to /0:Objects/0:Server/0:ServerStatus/0:CurrentTime.

Both approaches have their pros and cons. In general, the NodeId is less clumsy, but less descriptive. In this example, we prefer the NodeId and recreate the tree structure semantics with the help of MQTT mappings.

Below, there is a table of variables to use in the example. Most variables are read-only, except for the Temperature Setpoint, which allows us to actually control something.

|Variable             |NodeId                                      |BrowsePath                                                               |AccessLevel              |
|CurrentTime          |i=2258                                      |/0:Objects/0:Server/0:ServerStatus/0:CurrentTime                         |CurrentRead              |
|Humidity             |ns=3;s=AirConditioner_1.Humidity            |/0:Objects/3:BuildingAutomation/3:AirConditioner_1/3:Humidity            |CurrentRead              |
|Power Consumption    |ns=3;s=AirConditioner_1.PowerConsumption    |/0:Objects/3:BuildingAutomation/3:AirConditioner_1/3:PowerConsumption    |CurrentRead              |
|Temperature          |ns=3;s=AirConditioner_1.Temperature         |/0:Objects/3:BuildingAutomation/3:AirConditioner_1/3:Temperature         |CurrentRead              |
|Temperature Setpoint |ns=3;s=AirConditioner_1.TemperatureSetPoint |/0:Objects/3:BuildingAutomation/3:AirConditioner_1/3:TemperatureSetPoint |CurrentRead, CurrentWrite|
Code-Sprache: YAML (yaml)

Writing the Service YAML

The Service YAML is used to specify connections, endpoints and mappings for Connectware to handle. Create a new file in a text editor, e.g. opcua-example-service.yml. This example adds minimal content, to not distract the eye. For a complete reference of properties you can check out the Structure of the commissioning file.

Description and Metadata

These contain some general information. You can give a short description and add a stack of metadata. Regarding the metadata, only the name is required while the rest is optional. We will just use the following set of information for this lesson:

description: >
 OPC UA Example Service
 Cybus Knowledge Base - How to connect an OPC UA server

 name: OPC UA Example Service
Code-Sprache: YAML (yaml)


Parameters can be adjusted in the Connectware Web UI. We are defining the address details of our OPC UA server as parameters, so they are used as default, but can be customized in case we want to connect to a different server.


   type: string
   description: OPC UA Host Address

   type: integer
   description: OPC UA Host Port
   default: 48010
Code-Sprache: YAML (yaml)


The first resource we need is a connection to the OPC UA server.


   type: Cybus::Connection
     protocol: Opcua
       host: !ref opcuaHost
       port: !ref opcuaPort
       #username: myUsername
       #password: myPassword
Code-Sprache: YAML (yaml)

If you are using a username and password, you could also create parameters, to make them configurable. In our case the server does not require credentials.


   type: Cybus::Endpoint
     protocol: Opcua
     connection: !ref opcuaConnection
     topic: server/status/currenttime
       nodeId: i=2258

   type: Cybus::Endpoint
     protocol: Opcua
     connection: !ref opcuaConnection
     topic: building-automation/airconditioner/1/humidity
       nodeId: ns=3;s=AirConditioner_1.Humidity
       #browsePath: /0:Objects/3:BuildingAutomation/3:AirConditioner_1/3:Humidity
   type: Cybus::Endpoint
     protocol: Opcua
     connection: !ref opcuaConnection
     topic: building-automation/airconditioner/1/power-consumption
       nodeId: ns=3;s=AirConditioner_1.PowerConsumption
   type: Cybus::Endpoint
     protocol: Opcua
     connection: !ref opcuaConnection
     topic: building-automation/airconditioner/1/temperature
       nodeId: ns=3;s=AirConditioner_1.Temperature
   type: Cybus::Endpoint
     protocol: Opcua
     connection: !ref opcuaConnection
     topic: building-automation/airconditioner/1/temperature-setpoint
       nodeId: ns=3;s=AirConditioner_1.TemperatureSetPoint

   type: Cybus::Endpoint
     protocol: Opcua
     connection: !ref opcuaConnection
     topic: building-automation/airconditioner/1/temperature-setpoint
       nodeId: ns=3;s=AirConditioner_1.TemperatureSetPoint
       #browsePath: /0:Objects/3:BuildingAutomation/3:AirConditioner_1/3:TemperatureSetPoint
Code-Sprache: YAML (yaml)

Installing the Service YAML

  1. On the navigation panel, click Services.
  2. Click Upload Service.
  3. In the Create Service dialog, click Choose File and select commissioning file that we just created.
Screenshot of the Create Service dialog
  1. Click Install to install the service. The status section indicates the health of the service and the resources it defines.
  2. Once the service is installed, you must enable it. To enable a service, select it in the list and click Enable.
  3. You must authorize all permissions the service needs to operate. Make sure that all permissions are as intended and click Allow to enable the service.
Screenshot of the Service Details view (OPC UA)

Verifying the Data

To see the incoming data, click Data on the navigation panel. In the Data Explorer list, you can see the MQTT topic we specified in the commissioning file. To see data from a specific topic/endpoint, navigate to the corresponding topic in Available Topics list. This makes Connectware subscribe to topic and display its values on the Monitored Topics. In the History section on the bottom right, you will find all the data received since you subscribed to the topics.


First, we used an OPC UA client application to browse the address space. This allowed us to pick the variables of our interest and to reference them by their NodeId, or by BrowsePath. Given that information, we created a Service YAML and installed the Service on Connectware. In the Explorer we finally saw the live data on corresponding MQTT topics and are now ready to go further with our OPC UA integration.

Where to Go from Here

Why not store the OPC UA data in a time series database and display it on a dashboard for instance?

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