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Java SDK : OPC UA Pub/Sub & redundancy implementation
March 17, 2020
14:27, EEST
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July 25, 2018
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We have a 4.2 version of the Java SDK , and I wanted to know in this sdk what was the level of implementation of the OPC UA Pub/Sub specification and redundancy (Redundant Client Facet, Client Redundancy Server Facet, Redundancy Transparent Server Facet, Redundancy Visible Server Facet).

I saw that the SDK is supposed to support redundancy, but it is precised “requires application implementation”. Also, do you have any samples/examples on how to deploy such services with your SDK ?

Best regards,

March 17, 2020
15:12, EEST
Bjarne Boström
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April 3, 2012
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We do not yet have any version that would include any pubsub support. We are working on that (lets just say the number of support cases and other required fixes has been a lot bigger than estimated originally so less time for development). Probably at least some kind of beta (might not be public) version within early Q2 of this year. Note that first versions will not support everything. Therefore just saying “Pub/Sub” is not enough, since that means a lots of different things (UADP+UDP, MQTT, AMQP, binary or json encodings, is security needed? etc.). But e.g. for UADP+UDP we are quite close for making a beta release.

We do not have any examples for those redundancy facets. However are you yourself familiar what those actually means? We use the terms from the specification profiles, however what they actually mean might not be what you are thinking.

e.g. https://reference.opcfoundation.org/v104/Core/docs/Part7/6.6.116/, defines Redundant Client Facet. That means that the only thing that must be supported is the conformance unit “Redundancy Client”. And well, it is optional to support “Subscription Client TransferSubscriptions” (we support TransferSubscriptions).

However, “Redundancy Client” only just means (per https://apps.opcfoundation.org/ProfileReporting-v1.02/index.htm?ModifyProfile.aspx?ProfileID=c942a19b-8615-4c84-a81c-a20e26eec062) “Client supports Client redundancy. Clients that support Client redundancy can failover to another Client (requires some out of band communication).”. Since our SDK allows you to make more than one OPC UA Client, this is possible.. But it is upto you as an application level designer to come up with some kind of out of band communication way that the client knows that another client has failed for your specific use-case.

We will eventually make some examples, but priority for making those is not very high at the moment. Lets see once pubsub is done…..

March 26, 2020
12:30, EEST
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July 25, 2018
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First, thanks for your answer on Pub / Sub. We wanted to have an answer on what has been developped within the pubsub topic. From my understanding, you are working on several protocols at the same time, the most advanced one would be UADP+UDP.

For redundancy, as the specification defines it, I was thinking about failover between clients and between server. Is my interpretation correct ?
So, looking at your answer on Redundancy Client, for the server-side (e.g. https://reference.opcfoundation.org/v104/Core/docs/Part4/6.6.2/) we have to come up with our own solution either we want a transparent redundancy (involving some kind of hardware solution) or a visible redundancy.

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