How do you design and implement OPC UA for industrial IoT applications?

OPC UA implementation: define information model (standard models like PLCopen, custom extensions), configure address space (nodes, references, attributes), implement security (user authentication, message encryption, certificate management), design client-server architecture or pub-sub for scalability. Server-side: embed in PLC/device or deploy aggregation server, configure available data and methods. Client-side: develop applications using OPC UA SDKs, handle subscriptions efficiently. For IoT/cloud: OPC UA pub-sub with MQTT or AMQP transport, edge computing for data processing. Address network security, bandwidth optimization, and historian integration.