How to get changes of Server Diagnostic Nodes?

[johannwesely]

Hello,

I'm currently in the process of implementing alarms and conditions for our server. The customer has a requirement that an alarm should be triggered when ClientLastContactTime > 10 s.

I implemented a trigger schema that reacts to attribute changes via an AttributeFilter wich works well for instance nodes. However, with server diagnostic nodes, the attribute observer is not being reached.

I register my Node Observer with the AdressSpaceManager

//check if Input NodeIds from A&C Settings are present in the addressSpace and register Attribute Observer on them

		eventTriggers.entrySet().stream().forEach(entry -> {
			NodeId nodeId = NodeId.parse(entry.getKey());
			addressSpaceManager.getManagedNode(nodeId).ifPresent(node -> node.getFilterChain().addLast(new NodeEventAttributeObserver(loggerService, entry.getValue())));
		});

in NodeEventAttributeObserver i have this:

@Override
	public void setAttribute(AttributeFilterContext ctx, AttributeId attributeId, Object value) {
		Object oldValue = ctx.getAttribute(attributeId);
		ctx.setAttribute(attributeId, value);
		if (attributeId == AttributeId.Value) {
			eventTrigger.doTrigger(value, oldValue);
		}

	}

My question is now how can i get changes of server diagnostic nodes ? Any suggestions would be apprechiated.

Greetings Johann

[kevinherron]

There's no easy way to observe these, you'll want to poll instead. The value for diagnostic nodes is computed on the fly when read (via an AttributeFilter); it's never set/written, so there's never an attribute change to notify observers.

For your case specifically, note that ClientLastContactTime only updates when the client makes contact and freezes when it goes silent, so "no contact for >10s" isn't a value change anyone could observe; it becomes true just from time passing. You'd need a periodic timer that computes now - lastContactTime.

For this case in particular it would be easiest to skip the diagnostic nodes entirely and read live session state: server.getSessionManager().getAllSessions() and session.getLastContactTime() for each. This will work even when diagnostics haven't been enabled.