About redundancy - Specification vs UA.Netstandard usage|OPC UA Standard|Forum|OPC Foundation

Hi People, One question (1) and one recommendation (2), feel free to add a reply, even if it’s just a few words. Thank you.

We are currently using successfully the UA.Netstandard library as a client,
to read thousands of items, and we plan to add some support for redundancy.
(will submit pull requests if needed)

However, reading the specifications about Warm and Hot redundancy modes,
(e.g. OPC 10000-1: Services v1.04 – 6.6.2.4.5.3) I can see some steps labelled
“ActivateSampling” and “ActivatePublishing“.

(1)- I wonder what commands are expected in both steps, when sampling seems to be
handled on each monitored items, and publishing depends on the session.
My attempt would be like the pseudo-code under. Is my pseudo-code ok ?

[pseudo code for subscribing w/o sampling and publishing]
var subscription = new Subscription(session.DefaultSubscription)
{
   PublishingInterval = my_normal_period,
   PublishingEnabled = false,
}
var items = my_10000s_references.Select( 
   myref => new MonitoredItem(clientHandle: myref.index)
   {
     DisplayName = myref.display,
     StartNodeId = myref.nodeid,
     MonitoringMode = MonitoringMode.Disabled,
   };
);
subscription.AddItems(items);
session.AddSubscription(subscription);
subscription.Create();
[/pseudo code]

[pseudo code for activate sampling]
    // Activate sampling on items
    subscription.SetMonitoringMode(MonitoringMode.Report, subscription.MonitoredItems);
[/pseudo code]

[pseudo code for activate publishing]
    // Activate publishing mode
    subscription.SetPublishingMode(true);
[/pseudo code]

(2)– The specification says that the ServerStatus can help to compare multiple redundant servers,
and select the most appropriate one. So, imagine my client decides to jump from serverA (ServerStatus=100)
to serverB (ServerStatus=255).

The specification is really clear about what a client selecting to a new redundant server
is supposed to do, on the new server. But not what to do on the previous server, when the
server is still connected and replying.

I think I could maybe kill the subscription(s).. or maybe kill the session completely, and retry connecting later ?
Is this enough or too much ? What would be the recommended safe options ?

[pseudo code for killing subscription]
   // Kill subscription
   session.RemoveSubscription(subscription);
[/pseudo code]

Thanks in advance for your help in making the specification a bit more clear, at least in my head. 

In fact, writing this post helped me understand the SetMonitoringMode call, that basically sends to the 
server all the monitored ids to modify. (So it is slightly different from creating new monitored items
from scratch).

Julien.