Use OPC UA PubSub in C#

The code

using Opc.Ua.PubSub;
using Opc.Ua.PubSub.Configuration;

// PubSub is configured declaratively. This is the shape of it:
var config = new PubSubConfigurationDataType
{
    Connections = new PubSubConnectionDataTypeCollection
    {
        new PubSubConnectionDataType
        {
            Name             = "MqttConnection",
            Enabled          = true,
            PublisherId      = new Variant((ushort)1),
            TransportProfileUri = Profiles.PubSubMqttJsonTransport,
            Address = new ExtensionObject(new NetworkAddressUrlDataType
            {
                Url = "mqtt://localhost:1883",
            }),
            WriterGroups = new WriterGroupDataTypeCollection
            {
                new WriterGroupDataType
                {
                    Name              = "WriterGroup1",
                    Enabled           = true,
                    PublishingInterval = 1000,
                    WriterGroupId     = 1,
                    // DataSetWriters reference a PublishedDataSet by name
                },
            },
        },
    },
};

using UaPubSubApplication app = UaPubSubApplication.Create(config);
app.Start();
Console.WriteLine("publishing; inspect the broker with MQTT Explorer");

What it prints

# MQTT Explorer, topic opcua/writergroup1:
{"MessageId":"...","MessageType":"ua-data","PublisherId":"1",
 "Messages":[{"DataSetWriterId":1,"Payload":{"CurrentTime":{"Value":"2026-09-08T03:45:00.102Z"}}}]}

Notes

• PubSub is configured, not coded. Getting the configuration object right is the whole job, and it maps one-to-one onto the Part 14 model: connection, writer group, dataset writer, published dataset.
• Choose the encoding deliberately. Non-reversible JSON is smaller and human-readable but cannot be round-tripped because it discards type information.
• In JSON encoding, Good is 0 and is omitted. A missing status field means Good, not missing data: downstream consumers must be written knowing that.
• A subscriber joining mid-stream sees nothing until the next key frame. Set the key frame count with that in mind.
• PubSub has no session, so keys come from a Security Key Service rather than a handshake. Plan for it before you need security.

What breaks first

Last verified 7 September 2026 against OPC UA 1.05.07. OPC UA Connect is an educational resource and is not affiliated with the OPC Foundation.