# Example 6 - Full Transactional Data Flow (OPC UA)

This example demonstrates how to integrate an external DNS service with an OPC UA method using FlowSync. The configuration connects dns.google on the north side with a custom OPC UA method on the south side. The OPC UA server uses a `getIpForDomain` method that accepts a domain name (e.g., cybus.io) as input and returns the corresponding IP address as output.

You can access the OPC UA server via `opc.tcp://127.0.0.1:4841/UA/CybusOpcuaServer`.

* If the domain is successfully resolved, the method returns the IP address.
* If no DNS record is found, it returns a BadNotFound error.

For more information on the FlowSync configuration properties, see [Cybus:Node](/1-10-2/documentation/services/service-commissioning-files/resources/cybus-node.md#operation).

<figure><img src="/files/pjoitzJ7WPl6xiViXLeC" alt=""><figcaption></figcaption></figure>

{% file src="/files/pm74r2nPrXtLqJxrjeu1" %}

{% code lineNumbers="true" %}

```yaml
description: FlowSync - Example 6
metadata:
    name: example 6
    version: 1.0.0
resources:
    # ------------------------------------------------
    # Our Endpoints for dns.google (north side)
    # ------------------------------------------------

    googleDnsConnection:
        type: Cybus::Connection
        properties:
            protocol: Http
            connection:
                scheme: https
                host: dns.google

    dnsEndpoint:
        type: Cybus::Endpoint
        properties:
            topic: dns
            protocol: Http
            connection: !ref googleDnsConnection
            publishError: true
            read:
                path: /resolve

    # ---------------------------------------
    # Our OPCUA Server and Nodes  (south side)
    # ---------------------------------------

    opcuaServer:
        type: Cybus::Server::Opcua
        properties:
            hostname: 127.0.0.1
            allowAnonymous: true
            securityPolicies: ['None']
            securityModes: ['None']

    rootNode:
        type: Cybus::Node::Opcua
        properties:
            browseName: Cybus
            nodeId: ns=1;s=Cybus
            parent: !ref opcuaServer
            nodeType: Object

    getIpForDomainNode:
        type: Cybus::Node::Opcua
        properties:
            topic: getIpForDomain
            browseName: getIpForDomain
            nodeId: ns=1;s=getIpForDomain
            parent: !ref rootNode
            nodeType: Method # mark node as method
            operation: transaction
            inputArguments:
                - name: domain
                  dataType: String
                  description: the domain to resolve
            outputArguments:
                - name: ip
                  dataType: String
                  description: the IP address of the domain

    # ------------------------------------------------
    # The mappings forwarding requests and responses
    # ------------------------------------------------

    Mapping:
        type: Cybus::Mapping
        properties:
            mappings:
                - subscribe:
                      endpoint: !ref getIpForDomainNode
                  publish:
                      endpoint: !ref dnsEndpoint
                  rules:
                      - transform:
                            expression: >-
                                (
                                  {
                                    "id": $.id,
                                    "query": {
                                       "name": $.value.inputArguments[0].value
                                    }
                                  }
                                )
                - subscribe:
                      endpoint: !ref dnsEndpoint
                  publish:
                      endpoint: !ref getIpForDomainNode
                  rules:
                      - transform:
                            expression: >-
                                (
                                  {
                                    "id": $.id,
                                    "timestamp": $.timestamp,
                                    "value" : $.value.Status = 0 ? { 
                                       "outputArguments": [
                                          {
                                            "value": $.value.Answer[0].data
                                          }
                                       ]
                                    } : undefined,
                                    "error" : $.value.Status != 0 ? {
                                      "code": "BadNotFound",
                                      "message": "Domain not found"
                                    } : undefined
                                  }
                                )
```

{% endcode %}


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.cybus.io/1-10-2/documentation/services/flowsync/flowsync-example-6.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.