Lifecycle

This tutorial will cover the following topics:

Content

Server

The code in this example shows the three parts for OPC UA Server lifecycle management: Creating a Server, set configuration Server, and running the Server. Basic use of the Server module.

The OPC UA Server is based on a GenServer. Therefore it can spawn a new server by using start_link.

alias OpcUA.Server
{:ok, server_pid} = Server.start_link()

Server Configuration

The easiest way to configure the server is using the set_default_config/1 function, as shown in the following code:

:ok = Server.set_default_config(server_pid)

By default the hostname is given by the localhost, however it is possible to overwrite its value by using set_hostname/2:

:ok = Server.set_hostname(server_pid, "opex-server")

Note: Be aware of DNS configuration.

It is also possible to change the default port as follows.

:ok = Server.set_port(server_pid, 4040)

Note: Default port value is 4840.

Basic Authentication

Security is a fundamental aspect of OPC UA. It is possible to restrict access to the server by defining authorized users as shown bellow:

:ok = Server.set_users(server_pid, [{"alde103", "103alde"}, {"pedro", "ordep"}])

In this example, we declare two users (alde103 and pedro) with their respective passwords.

Note: This is not the best way to secure your OPC UA Server. Refer to Security tutorial for a better approach.

Start / Stop

At this point, the server will not accept requests yet. Use the start/1 function to start the server explicitly.

:ok = Server.start(server_pid)

The Server can be stopped with the stop_server/1 function.

:ok = Server.stop_server(server_pid)

Client

The code in this example shows the three parts for OPC UA Client lifecycle management: creating, configuring, and connecting a client to a server. Basic use of the Client module.

The OPC UA Client is based on a GenServer. Therefore it can spawn a new server by using start_link.

alias OpcUA.Client
{:ok, client_pid} = Client.start_link()

Configuration

The client can be configured using the following function,

:ok = Client.set_config(client_pid)

it is possible to overwrite some connection parameters (such as timeouts) by using set_hostname/2,

config = %{
  "requestedSessionTimeout" => 12000,
  "secureChannelLifeTime" => 6000,
  "timeout" => 500
}
:ok = Client.set_config(client_pid, config)

Note: Use get_config/1 function to check the current client configuration.

Connection

OPC UA provides a client-server communication model that includes status information. This status information is associated with a session.

The user can check the connection status through get_state/1 function:

{:ok,  "Disconnected"} = Client.get_state(client_pid)

By URL

The Client can connect to a Server by using connect_by_url/2 and providing the Server's URL as follows:

url = "opc.tcp://localhost:4048/"
:ok = Client.connect_by_url(client_pid, url: url)
{:ok,  "Session"} = Client.get_state(client_pid)

By Username

If the Server has some user restriction, the client must provide the username and password to access the Server. If this is your case, use connect_by_username/2

url = "opc.tcp://localhost:4840/"
user = "alde103"
password = "103adle"
:ok = Client.connect_by_username(client_pid, url: url, user: user, password: password)

No Session

There may be situations where a session is not required. For those cases use connect_no_session/2

url = "opc.tcp://localhost:4048/"
:ok = Client.connect_no_session(c_pid, url: url)
{:ok,  "Secure Channel"} = Client.get_state(c_pid)