Message-Bus

Your config should include a vip-address in it.

C4 model aims for simplicity. It eases early architectural work, at a moment when many details are still uncertain. It facilitates team discussion with people who are not all familiar with all the subtleties of the UML notation.

It does not intend to be a general diagramming technique for everything. So no, there is no business process modelling. The context level diagram provides some more information as use case-diagrams about what the user exchanges with the system. But it stops there. There's still a market for BPMN (or for UML activity diagrams which were demonstrated to be as expressive as a BPMN).

It does not either intend to replace infrastructure diagramming or hardware design. It specifically aims at the needs of software intensive systems: what software runs where and how. UML deployment diagrams are not dead if details are needed. This being said, I think it's easy to add some boxes to represent firewalls, as if they were software elements, if it is needed to understand the architecture. And API gateways definitively get to the C4 picture (in a style similar to this example).

C4 level 3 is the component. The 4th level allows you to use any existing modelling notation to show more details. There is no need to reinvent the wheel. If the component is still very complex, you may use the full power of UML and its recursively to go as deeper as needed (and if needed only).

It's as needed. You may probably begin your architecture, just identifying that a database is needed. But maybe later, you'd have several schemas in the environment and you need to disambiguate. Or just want to document the name.

Certainly, but this is out of scope here.

At first you must familiarize yourself with the theory of "cold" and "hot" observables. Here is the definition from the Introduction to RX.

1. Cold are sequences that are passive and start producing notifications on request (when subscribed to).
2. Hot are sequences that are active and produce notifications regardless of subscriptions.

What you want is a hot observable, and the problem is that the Observable.Create method creates cold observables. But you can make any observable hot by using the Publish operator. This operator provides a way to have a single underlying subscription shared by multiple independent observers. Example:

YAML::Node is a reference type already, so returning it from a function doesn’t make a deep copy. It’s also mutable, so you can just edit it and the change will update the root node.