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Getting 'subscription id is not valid' after restarting software OPC UA server

Eike Saathoff

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12/13/2021 - 08:03

Hi there,

we operate an OPC UA server in our company, which obtains data from several machines via a proprietary protocol and then provides this data via OPC UA. The service works fine 99% of the time, but I have to restart it sometimes because it hangs. When I restart this service now, I often get the error: ‘The subscription id is not valid’ on the OPC UA clients. The error disappears only after I have restarted the service 1 to x times. This is often annoying, because the data is then not recorded over the entire period of freezing.

Can anyone give me a hint on what this could possibly be caused by? We have speculated that after restarting the service, the subscriptionIds assignments are no longer present and thus no data can be received.

We are using a KepserverEx and a SCADA system to retrieve the data.

Unfortunately I don’t have access to the source code, as our machine manufacturer provides this service, but they are not able to fix the problems with this service.

I am grateful for any help.

Best regards

Randy Armstrong

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12/13/2021 - 17:42

This page explains the process:
https://reference.opcfoundatio…..Part4/6.7/

Based on your description of the problem it sounds like the issue is your client is not properly handling dropped subscriptions so the fix would be to restart the client – not the server.

Eike Saathoff

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12/14/2021 - 00:08

Thanks for your reply! I will check this shortly.

I just found it suspicious that this is the only OPC UA server that pops this error and it occurs for all 3 clients I tested it with: KepserverEx, SCADA and UAExpert.

Then we would try to automate this reconnect process due to the subscription errors. Maybe it would be possible to initiate a reconnect when the error occurs.

Best regards

Randy Armstrong

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12/14/2021 - 08:53

It is possible the Server is returning the wrong error code in some other context which causes the Clients to hiccup. That said, the process outlined in the spec require Clients to re-create subscriptions after an interruption if they can’t resume the old ones.

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