OPC-UA without Discovery

Ignition
1

How can we connect to an OPC-UA server without discovery?

I have no issue at all browsing, reading, writing, or executing call functions with the FreeOpcUa/python-opcua application.
https://github.com/FreeOpcUa/python-opcua

image
image1447Ă—630 19.5 KB

2

Discovery isn’t optional. In many cases the endpoint URL and discovery URL will be the same, so try that to start.

1 Like
3

Can you give me a reference that shows discovery is required for OPC-UA standard spec. So that I may use this reference in my support request with my device OEM?

…and thank you for the quick response.

4

Part 4, section 5.4.1 Discovery Service Set Overview:

Every Server shall have a Discovery Endpoint that Clients can access without establishing a Session.

All OPC UA clients I’ve seen use a 2-step connect process:

  1. open a connection, call GetEndpoints on the “discovery URL” to get a list of endpoints, close this connection.
  2. scan through that list of endpoints to find one that matches what was configured (endpoint URL, security, etc…), and then open a connection to that endpoint.

In many cases the “discovery URL” and chosen “endpoint URL” are the same, but there are situations where they can be different.

1 Like
5

A little later in this section there’s some language that allows discovery services to be disabled for a server, which requires that a client be able to cache all the necessary information to connect to that endpoint without going through discovery first. This also implies that for a server that will have discovery services disabled it should be configurable, so that they can be enabled for a client to connect, do discovery, and cache the chosen endpoint in the first place.

Ignition’s client does not support this and I don’t think figuring out how I can make this work in a backwards compatible manner is going to be high priority.

6

I was looking for a good case to show a hardware OEM that they need to configure discovery properly and why it was important. Was that OPC Foundation Spec document? “Part 4, section 5.4.1 Discovery Service Set Overview”

Thanks again.

7

Yes, it was OPC UA Spec version 1.03, Part 4.

1 Like