Example: OPC

12 min

End-to-end walkthrough: configure the Litmus Edge OPC UA server hierarchy, set security, add a user, and import existing DeviceHub tags.

Setup

from litmussdk import opc

The Litmus Edge OPC UA server can publish DeviceHub tags as OPC UA nodes for upstream OPC clients (SCADA, historians, etc.).

1. Inspect Current Hierarchy

root = opc.get_root_node()
top_level = opc.get_node_by_paths([])    # children of root

2. Reset to a Clean State

Use with caution; clears the hierarchy.

opc.reset_all_hierarchy()

3. Build a Hierarchy

plant_node = opc.add_node_folder(parent_id=root.id, name="Plant1")
line1 = opc.add_node_folder(parent_id=plant_node.id, name="Line1")
pump = opc.add_node_device(parent_id=line1.id, name="Pump-01", device_id=device_id)

4. Import All Tags from a DeviceHub Device

opc.import_all_dh_tags(device_id=device_id, parent_node_id=pump.id)

5. Add a Specific Tag

opc.add_node_tag(
    parent_id=pump.id,
    tag_id=pressure_tag_id,
    name="Pressure",
)

6. Add a Logic Node (Computed)

opc.add_node_logic(
    parent_id=pump.id,
    name="EfficiencyEstimate",
    formula="Pressure * FlowRate / 1000",
)

7. Update Security and Auth

current = opc.get_security_and_auth_settings()

opc.change_security_and_auth_settings(
    security_modes=["SignAndEncrypt"],
    security_policies=["Basic256Sha256"],
    user_token_types=["UserName"],
)

8. Service Configuration

config = opc.get_service_config()

opc.change_service_config(
    port=4840,
    application_name="LitmusEdge-OPC-UA",
    enable_anonymous=False,
)

# Restart the OPC UA service to apply
opc.start_stop_opc(action="restart")

9. Server Certificates and Metrics

certs = opc.get_server_certificates()
metrics = opc.get_server_metrics()

10. Export the Hierarchy as JSON

Useful for snapshotting or for the Air gap Features builder.

hierarchy_json = opc.export_as_json()

# Re-import on another Edge:
opc.import_json(hierarchy_json)