Use Greengrass OPC-UA to Communicate with Multiple Industrial Equipment

Greengrass supports OPC-UA, an information exchange standard for industrial communication. OPC-UA allows you to ingest and process messages from industrial equipment and deliver them to devices in your Greengrass group or to the cloud based on rules you define.

The Greengrass implementation of OPC-UA supports certificate-based authentication. It is based on an open source implementation, and is fully customizable. You can also bring your own implementation of OPC-UA, and implement your own support for other custom, legacy, and proprietary messaging protocols.

In this section we will cover the following steps:

• Connect to an existing multiple OPC-UA servers.
• Monitor multiple existing OPC-UA nodes within that server.
• Get called back when the monitored node's value changes.

Architectural Overview

Greengrass implements OPC-UA as a Lambda function in NodeJS. Since Lambda functions running on Greengrass cores have access to network resources, you can create Lambda functions that proxy information from your existing OPC-UA servers over TCP to other functions or services in your Greengrass group.

Under this architecture, we provide the following additional features for customer to use:

• published_nodes.json, used to configured how many OPC-UA nodes in dedicated OPC-UA server need to be monitored.
• cert_config.json, used to configure the path of server certificates.
• client_config.json, used to configure some client options and time interval to check publishednodes.json modification.
• system_status.txt, used to check if the system is alive or not.

You can configure Greengrass to have a long-lived connection to your OPC-UA server(s), and, using OPC-UA Subscriptions, you can have your OPCUA_Adapter Lambda function monitor changes to pre-defined nodes. Any change to those nodes triggers a Publish event from the OPC-UA server, which will be received by your Lambda function, and republished into predefined topic names.

Set Up a Test OPC-UA Server

Use the following commands to set up a test OPC-UA server. Or, if you already have an OPC-UA server you'd like to use instead, you may skip this step.

git clone git://github.com/node-opcua/node-opcua.git
cd node-opcua
git checkout v0.0.65
npm install
node bin/simple_server

The server produces the following output:

[ec2-user@<your_instance_id> node-opcua]$ node bin/simple_server
  server PID          : 28585

registering server to :opc.tcp://<your_instance_id>4840/UADiscovery
err Cannot find module 'usage'
skipping installation of cpu_usage and memory_usage nodes
  server on port      : 26543
  endpointUrl         : opc.tcp://<your_instance_id>us-west-2.compute.internal:26543
  serverInfo          :
      applicationUri                  : urn:54f7890cca4c49a1:NodeOPCUA-Server
      productUri                      : NodeOPCUA-Server
      applicationName                 : locale=en text=NodeOPCUA
      applicationType                 : SERVER
      gatewayServerUri                : null
      discoveryProfileUri             : null
      discoveryUrls                   : 
      productName                     : NODEOPCUA-SERVER
      buildInfo                       :
      productUri                      : NodeOPCUA-Server
      manufacturerName                : Node-OPCUA : MIT Licence ( see http://node-opcua.github.io/)
      productName                     : NODEOPCUA-SERVER
      softwareVersion                 : 0.0.65
      buildNumber                     : 1234
      buildDate                       : Thu Aug 03 2017 00:13:50 GMT+0000 (UTC)

  server now waiting for connections. CTRL+C to stop

You could setup many OPC-UA servers concurrently.

Make sure your Greengrass Group is ready

• Create a Greengrass group (find more details in Configure AWS IoT Greengrass on AWS IoT.)
• Set up a Greengrass Core on one of the supported platforms (Raspberry-pi for example)
• Set up your Greengrass Core to be able to run nodejs12.x Lambda functions.
• Set up local resource to access the configurable json file, /etc/greengrass/opcua-adapter/config/system_status.txt, for the additional features as described in the Architecture section.

Use Greengrass OPC-UA to Interact with your OPC-UA Server

1. Prepare your Lambda function and relocate the config foler.

   • Get the code for an OPC-UA adapter Lambda function from GitHub:

     git clone https://github.com/andysun2015/OPCUA-Adapter-For-Multiple-Opcua-Server.git
     cd greengrass-opcua-adapter-nodejs
     npm install
     

   • Patch the factories.js

     git apply patch/factories.patch
     

   • Relocate the folder greengrass-opcua-adapter-nodejs/config to /etc/greengrass/opcua-adapter/config defined in config_agent.js.

   • Download AWS IoT Greengrass Core SDK Software For Nodejs. and copy aws-greengrass-core-sdk folder into node_modules folder.

     # copy aws-greengrass-core-sdk to node_modules
     git clone https://github.com/aws/aws-greengrass-core-sdk-js.git
     cd aws-greengrass-core-sdk-js/
     cp -fr aws-greengrass-core-sdk OPCUA-Adapter-For-Multiple-Opcua-Server/greengrass-opcua-adapter-nodejs/node_modules/

   Note:

   • The relocated path must also defined in Lambda configuration in IoT Core console, or the Lambda function wouldn't find the path or have no access right to this path!
   • There's a future work here which would make this path adjustable!

2. Configure the server and monitored nodes

   Modify the field EndpointUrl in the file published_nodes.json in config folder which contain the server IP and Port that you want to connect to, as well as the node Ids you would like to monitor. Here's the example:

    [
     {
        "EndpointName": "UNO-2484G",
        "EndpointUrl": "opc.tcp://localhost:26543",
        "OpcNodes": [
        {
            "Id": "ns=1;s=Temperature",
            "DisplayName": "M140001"
        },
        {
            "Id": "ns=1;s=FanSpeed",
            "DisplayName": "M140002"
        },
        {
            "Id": "ns=1;s=PumpSpeed",
            "DisplayName": "M140003"
        }
        ]
     }
    ]

   In this case, we are connecting to an OPC-UA server running on the same host as our Greengrass Core, on port 26543, and monitoring multiple nodes that has an OPC-UA Id 'ns=1;s=Temperature', 'ns=1;s=FanSpeed', and 'ns=1;s=PumpSpeed'.

3. Configure to authenticate trusted server

   Modify the field CertPath in cert_config.json, which is used to tell OPC-UA client the received OPC-UA Server certificate in Ceritificate List is matched or not:

   [
    {
       "CertPath": "Directory"
    }
   ]

   Once there's no any certificate matched in the CertPath, then the OPC-UA client wouldn't go on the communication with the OPC-UA server.

4. Configure json file polling time of Lambda. MOdify the field checkServerConfigInterval in client_config.json to adjust the polling interval in mini second of Lambda reading json file.

   [
    {
       "keepSessionAlive": "true",
       "connectionStrategy": {
       "maxRetry":100000,
       "initialDelay":2000,
       "maxDelay":10000
       },
       "checkServerConfigInterval":1000
    }
   ]

   In this case of "checkServerConfigInterval":1000, Lambda function will poll json file once 1 second.

5. Upload your Lambda

   Create a Greengrass Lambda function. You can find more details on how to do that in Configure the Lambda Function for AWS IoT Greengrass. In a nutshell, create a Lambda function code archive by doing the following:

   # Archive the whole directory as a zip file
   zip -r opcuaLambda.zip * -x \*.git\*

   Add this Lambda to your Greengrass Group. Details are, again, in: Configure the Lambda Function for AWS IoT Greengrass.

6. Configure and Deploy the Lambda function to your Greengrass Group

   After creating your AWS Lambda function, you add it to your Greengrass Group. Follow the instructions in same section as above.

   • Make sure to specify the Lambda function as Long-Running.
   • Give it at least 64MB of memory size.

   You can now create a deployment with your latest configuration. You can find details in Deploy Cloud Configurations to an AWS IoT Greengrass Core Device.

Verify that your Lambda function is receiving OPC-UA Publishes and posting them onto Greengrass

As described in the Architecture section, your Lambda function should start receiving messages from your OPC-UA server. If you are using your own custom OPC-UA server, make sure you trigger a change in the OPC-UA node Id you specified, so that you see the change received by your Lambda function. If you are using the example server above, the PumpSpeed node is configured to simulate a series of consecutive updates, so you should expect your Lambda function to receive multiple messages a second.

You can see messages received by your Lambda function in one of two ways:

• Watch the Lambda function’s logs

  You can view the logs from your Lambda function by running the following command:

   sudo cat ggc/var/log/user/us-west-2/your_account_id/your_function_name.log 

  The logs should look similar to:

  [2017-11-14T16:33:09.05Z][INFO]-started subscription : 305964
  
  [2017-11-14T16:33:09.05Z][INFO]-monitoring node id =  ns=1;s=PumpSpeed
  
  [2017-11-14T16:33:09.099Z][INFO]-monitoredItem initialized
  
  [2017-11-15T23:49:34.752Z][INFO]-Publishing message on topic "/opcua/server/node/MyPumpSpeed" with Payload "{"id":"ns=1;s=PumpSpeed","value":{"dataType":"Double","arrayType":"Scalar","value":237.5250759433095}}"
  

• Configure Greengrass to forward messages from your Lambda function to the IoT Cloud.

  Follow the steps outlined in Verify the Lambda Function Is Running on the Device to receive messages on the AWS IoT Core console.

Note:

• Make sure there is a Subscription from your Lambda function going to the IoT Cloud. Details are in Configure the Lambda Function for AWS IoT Greengrass.
• Since messages are forwarded to the cloud, make sure you terminate either the example server you configured above, or stop the Greengrass core, so that you don't end up publishing a lot of messages to IoT cloud and getting charged for them!

License

This solution is licensed under the MIT-0 License. See the LICENSE file.