Difference between Discovery URL and Endpoint URL

[jchirantan]

Hi @kevinherron,

Can you explain what is the difference between Discovery URL and Endpoint URL?
Also, how the implementation of creating client and connecting to client, will change for these 2 types of URL

[kevinherron]

The Discovery URL is where you can connect to call the Discovery services, e.g. FindServers and GetEndpoints.

The EndpointDescriptions you receive in the GetEndpoints call will have an Endpoint URL in them. This is the URL you will use when connecting with the intention of creating a Session.

For many servers these will be the same, but it’s possible they are not, e.g. the discovery url could be opc.tcp://hostname:4840/discovery and the session endpoint url could be opc.tcp://hostname:4840 or even have a different port or something.

This is important because the way most clients are written, not just in Milo, is to connect in 2 steps:

1. Connect without security, call FindServers/GetEndpoints, select an EndpointDescription matching what the user has configured, disconnect.
2. Connect to the endpoint using the EndpointDescription chosen in step 1, usually with security, create/activate a session, etc…

The thing to take away is that the URL you used to call the discovery services and the URL in the EndpointDescription for the endpoint you actually want to connect to might be different, and this difference is important.

[jchirantan]

So, with Endpoint URL also, we have to call "DiscoveryClient.getEndpoint()", find endpoint description and then connect to that endpoint. Right?

[kevinherron]

Call it what you want, discovery or endpoint URL - if you don't yet have an EndointDescription, you have to call DiscoveryClient.getEndpoints to get one.

[jchirantan]

Okay, Thanks!!