OPC UA Client

This page describes how the Connectware can act as an OPC UA client. The Connectware can also act as a OPC UA server.

OPC UA Subscriptions

OPC UA distinguishes between session, subscriptions and monitored items.

• Each Connectware connection creates exactly one session in the OPC UA terminology, where the Connectware acts as a client towards the server.

• Within one session, the set of data endpoints are grouped in subscriptions. A subscription carries parameters like publishInterval and maxNotificationsPerPublish so that it controls the data flow between server and client.

• Within each subscription, the actual data endpoints (also called nodes) are subscribed as monitored items. The monitored items are configured by parameters like nodeId, attributeId, samplingInterval, so monitored items control the collection of the data by the server. Each network request for creating these can create one or multiple monitored items per request.

Connectware Subscriptions

The Connectware tries to abstract this complexity away, combining as many endpoints as possible into the same subscription, and also monitored items creation into the same request. This is done according to the following criteria:

• Each OPC UA Cybus::Connection resource creates exactly one session

• Within this session, all OPC UA Cybus::Endpoint resources with the same publishInterval property are combined into one subscription. This holds even across different service commissioning files using inter-service referencing, see here. Hence, enabling/disabling additional services with additional endpoints will add or remove those endpoints from the currently available subscription.

• Every OPC UA Cybus::Endpoint resource corresponds to one monitored item

• Within one subscription and within the same service commissioning file, all endpoints (= monitored items) with the same samplingInterval property are combined into one common creation request. This “create monitored items request” is working very efficiently also for thousands of monitored items.

Due to its importance, the relation of the OPC UA terminology to Connectware resources is listed once more:

Session

One Cybus::Connection is exactly one session. (OPC UA reference: 5.6.1 Session)

Subscription

All Cybus::Endpoints with the same publishInterval in the same connection, regardless of service commissioning file. (OPC UA reference: 5.13.1 Subscription)

Monitored items

All Cybus::Endpoints. (OPC UA reference: 5.12.1 MonitoredItem)

Create Monitored Items Request

The monitored items within one service, one connection, and with the same samplingInterval are combined into a single “create monitored items request” (OPC UA reference: 5.12.2 CreateMonitoredItems)

Subscription Limitations

Some OPC UA servers are known for imposing certain limits on the number of monitored items, either in total, or per subscription, or per request.

In particular, an embedded OPC UA server on a Siemens S7-1500 or S7-1200 PLC is known for certain restrictions, see System limits of OPC UA Server.

• For example, the maximum number of monitored items within one “create monitored items request” might limited to e.g. 1000 nodes. This limit can even be looked up in the OPC UA node with nodeId ns=0;i=11714. On the Connectware side this limit must be taken into account by setting the property maxMonitoredItemsPerCall in the Cybus::Connection resource to the respective value. This will ensure to split larger requests so that all requests stay within this limit.

• Also, some maximum number of monitored items in total might be configured in the TIAPortal project. Unfortunately it is not known how to look up this value except directly in TIAPortal. If such a value is set, it is not possible for the Connectware to create any larger number of endpoints than this value.

Regarding the created subscriptions: As of today, subscriptions are combined only by the publishInterval parameter. The remaining properties related to subscriptions are currently taken only from the first endpoint to be subscribed, while differing settings at subsequent endpoints are currently ignored. This concerns the following endpoint properties: requestedLifetimeCount, requestedMaxKeepAliveCount, maxNotificationsPerPublish, priority.

Example

This is an example configuration snippet with three endpoints (without the connection configuration):

resources:
    spindleSpeed:
        type: Cybus::Endpoint
        properties:
            protocol: Opcua
            connection: !ref opcuaConnection
            subscribe:
                nodeId: 'ns=1;s=spindleSpeed'
                publishInterval: 1000
                samplingInterval: 100
                maxNotificationsPerPublish: 100
    powerConsumption:
        type: Cybus::Endpoint
        properties:
            protocol: Opcua
            connection: !ref opcuaConnection
            subscribe:
                nodeId: 'ns=1;s=powerConsumption'
                publishInterval: 1000
                maxNotificationsPerPublish: 50
                samplingInterval: 1000
    temperature:
        type: Cybus::Endpoint
        properties:
            protocol: Opcua
            connection: !ref opcuaConnection
            subscribe:
                nodeId: 'ns=1;s=temperature'
                publishInterval: 15000
                samplingInterval: 15000

In the above example, two subscriptions will be created. One with publishInterval set to 1000ms and maxNotificationsPerPublish set to 100, the other one with publishInterval set to 15.000ms. The sampling of the individual source values will be set as expected by the specified samplingInterval property, but remember that OPC UA does not offer a fixed data sampling but rather applies a change-of-value filter to each particular data point automatically.

Security Settings

For production use, the connection to the OPC UA server should only be established using the security profile SignAndEncrypt. Any other security profile bears the risk that the communication between client and server can easily get manipulated or compromised. Per default, the built-in OPC UA server only allows connections with SignAndEncrypt security setting enabled (in the property securityModes). Please use your Connectware credentials when authenticating to the OPC UA server by Connectware username and password user token.

Connection Properties Endpoint Properties

Example Commissioning Files

Simple example

This is a simple OPC UA connectivity example that only subscribes to the “Server Status” node of an OPC UA server. The proposed node (endpoint) can also be used if the server would otherwise close the connection, which has been observed for some specific versions of OPC UA servers on a S7 PLC.

The example will need some OPC UA server available in your network:

---
description: >

    Simple OPC UA connectivity example

metadata:
    name: Simple OPC UA connectivity
    version: 1.0.0
    icon: https://www.cybus.io/wp-content/uploads/2019/03/Cybus-logo-Claim-lang.svg
    provider: cybus
    homepage: https://www.cybus.io

parameters:
    opcuaHost:
        type: string
        description: OPC-UA Host
        default: 172.17.0.1

    opcuaPort:
        type: integer
        default: 4840

    opcuaUser:
        type: string
        default: ''

    opcuaPass:
        type: string
        default: ''

resources:
    opcuaConnection:
        type: Cybus::Connection
        properties:
            protocol: Opcua
            connection:
                host: !ref opcuaHost
                port: !ref opcuaPort
                username: !ref opcuaUser
                password: !ref opcuaPass

    serverStatusEndpoint:
        type: Cybus::Endpoint
        properties:
            protocol: Opcua
            connection: !ref opcuaConnection
            subscribe:
                nodeId: ns=0;i=2259
                samplingInterval: 2000

Download:

1KB

opcua-simple-example.yml

More complex example

More complex example including an OPC UA server container from public docker hub:

---
description: >

    Simulated OPC UA server

metadata:
    name: Simulated OPC UA
    version: 1.0.1
    icon: https://www.cybus.io/wp-content/uploads/2019/03/Cybus-logo-Claim-lang.svg
    provider: cybus
    homepage: https://www.cybus.io

parameters:
    opcuaHost:
        type: string
        description: OPC-UA Host
        default: 172.17.0.1

    opcuaPort:
        type: integer
        default: 50000

    opcuaUser:
        type: string
        default: user

    opcuaPass:
        type: string
        default: user

definitions:
    CYBUS_MQTT_ROOT: cybus-factory/opcua

resources:
    machineSimulatorContainer:
        type: Cybus::Container
        properties:
            image: mcr.microsoft.com/iotedge/opc-plc
            ports:
                - !sub '${opcuaPort}:50000/tcp'
            command:
                - --unsecuretransport
                - --autoaccept
                - --defaultuser=user
                - --defaultpassword=user

    opcuaConnection:
        type: Cybus::Connection
        properties:
            protocol: Opcua
            connection:
                host: !ref opcuaHost
                port: !ref opcuaPort
                username: !ref opcuaUser
                password: !ref opcuaPass

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

    dipData:
        type: Cybus::Endpoint
        properties:
            protocol: Opcua
            connection: !ref opcuaConnection
            topic: dip-data
            subscribe:
                nodeId: ns=2;s=DipData

    alternatingBool:
        type: Cybus::Endpoint
        properties:
            protocol: Opcua
            connection: !ref opcuaConnection
            topic: alternating-bool
            subscribe:
                nodeId: ns=2;s=AlternatingBoolean

    negativeTrendData:
        type: Cybus::Endpoint
        properties:
            protocol: Opcua
            connection: !ref opcuaConnection
            topic: negative-trend-data
            subscribe:
                nodeId: ns=2;s=NegativeTrendData

    positiveTrendData:
        type: Cybus::Endpoint
        properties:
            protocol: Opcua
            connection: !ref opcuaConnection
            topic: positive-trend-data
            subscribe:
                nodeId: ns=2;s=PositiveTrendData

    randomSignedInt:
        type: Cybus::Endpoint
        properties:
            protocol: Opcua
            connection: !ref opcuaConnection
            topic: random-signed-int32
            subscribe:
                nodeId: ns=2;s=RandomSignedInt32

    randomUnsignedInt:
        type: Cybus::Endpoint
        properties:
            protocol: Opcua
            connection: !ref opcuaConnection
            topic: random-unsigned-int32
            subscribe:
                nodeId: ns=2;s=RandomUnsignedInt32

    spikeData:
        type: Cybus::Endpoint
        properties:
            protocol: Opcua
            connection: !ref opcuaConnection
            topic: spike-data
            subscribe:
                nodeId: ns=2;s=SpikeData

    stepUp:
        type: Cybus::Endpoint
        properties:
            protocol: Opcua
            connection: !ref opcuaConnection
            topic: step-up
            subscribe:
                nodeId: ns=2;s=StepUp

Download:

3KB

opcua-example.yml

Output Format On Reading

If data is read from OPC UA the output will be provided as JSON object with value and timestamp.

The given timestamp is the OPC UA “Source Timestamp” which was set on the data source side, see https://reference.opcfoundation.org/v104/Core/docs/Part4/7.7.3/

{ 'timestamp': '<unix timestamp in ms>', 'value': 'value' }

Note: If 64-bit integers are being used (which are unsupported in JSON, but are supported in Javascript by the BigInt class), the value is returned as a string that contains the decimal number.

Output Format On Writing

When data is written to an OPC-UA endpoint, you will get the result of the operation over the /res topic like this:

{ 'id': 29194, 'timestamp': 1629351968526, 'result': { 'value': 0 } }

Input Format

If data is written to OPC UA it must be provided as JSON object

{ 'value': '<value>' }

Reconnection Behaviour

In OPC UA connections – just with any network connections – it can happen that the connection is lost. In that case the Connectware’s OpcuaConnection will automatically switch into reconnecting state and repeatedly try to re-establish the connection. The exact behaviour on how often this is tried can be controlled by the optional connectionStrategy properties, see Connection Properties. The important property is maxDelay which sets the maximum waiting time (delay) between consecutive re-tries, in milliseconds. The waiting time will start with the value initialDelay, then be increased step by step, until the maxDelay value.

Example with initially 500ms waiting time, increasing up to 10 seconds:

resources:
    myConnection:
        type: Cybus::Connection
        properties:
            protocol: Opcua
            connection:
                host: !ref opcuaHost
                port: !ref opcuaPort
                options:
                    connectionStrategy:
                        initialDelay: 500
                        maxDelay: 10000

For further details see also the documentation of the internally used package backoff, https://www.npmjs.com/package/backoff

Events for OPC UA

Event subscriptions can be created in the connectware by adding the properties fields and eventTypes to the Cybus::Endpoint resource as shown in the example below.

The names for the fields should be Qualified Names. Often, this will require the field name to also contain a namespace identifier, for example 4:MyQualifiedName.3:SubitemQualifiedName. Also, the field names often additionally need a sub-type, which can be specified using a dot notation after the name.

---
description: >

    Simple OPC UA connectivity example

metadata:
    name: example for opcua connectivity
    version: 1.0.0
    icon: https://www.cybus.io/wp-content/uploads/2019/03/Cybus-logo-Claim-lang.svg
    provider: cybus
    homepage: https://www.cybus.io

parameters:
    opcuaHost:
        type: string
        description: OPC-UA Host
        default: 172.17.0.1

    opcuaPort:
        type: integer
        default: 4840

    opcuaUser:
        type: string
        default: ''

    opcuaPass:
        type: string
        default: ''

resources:
    opcuaConnection:
        type: Cybus::Connection
        properties:
            protocol: Opcua
            connection:
                host: !ref opcuaHost
                port: !ref opcuaPort
                username: !ref opcuaUser
                password: !ref opcuaPass

    # Listen to all events from the server node
    # A list of eventTypes can be selected
    serverEventsEndpoint:
        type: Cybus::Endpoint
        properties:
            protocol: Opcua
            connection: !ref opcuaConnection
            subscribe:
                nodeId: i=2253
                eventTypes:
                    - 'i=85'
                fields:
                    - 'EventType'
                    - 'ReceiveTime'
                    - 'Message'
                    - 'SourceName'
                    - 'Severity'

Download:

1KB

opcua-events-example.yml

Accessing Status Codes for Values

The quality of a data value in OPC UA is represented by predefined status codes. The `statusCode` is transferred to the `$context` object and can be retrieved within the rule engine of a Cybus::Endpoint via `$context.raw.statusCode` as shown in the example below.

description: OPC UA Status Code Example
metadata:
    name: OPC UA Status Code Example
    version: 1.0.0
parameters:
    ipAddress:
        type: string
    port:
        type: integer
        default: 4334
    samplingIntervalMs:
        type: number
        default: 1000
    publishIntervalMs:
        type: number
        default: 1000
resources:
    opcuaConnection:
        type: Cybus::Connection
        properties:
            protocol: Opcua
            connection:
                host: !ref ipAddress
                port: !ref port

    A_000:
        type: Cybus::Endpoint
        properties:
            protocol: Opcua
            connection: !ref opcuaConnection
            subscribe:
                nodeId: ns=1;s=0
                samplingInterval: !ref samplingIntervalMs
                publishInterval: !ref publishIntervalMs
            rules:
                - transform:
                      expression: |
                          { 
                            "statusCode": {
                              "name": $context.raw.statusCode.name,
                              "value": $context.raw.statusCode.value,
                              "description": $context.raw.statusCode.description
                            },
                            "value": $.value,
                            "timestamp": $.timestamp
                          }
            topic: A/000

Download:

1KB

opcua-statusCodes-example.yml