There are many diagrams in your courses that use symbols for services, nodes, clusters etc. The exact architectural meaning of each of the icons used in the diagrams is not clear - is this explained somewhere? For example in Design of a Distributed Messaging Queue: Part 1 and later pages you have the following icon type labels:
- server - pretty clear these are individual servers but you seem to have different icons for compute servers and database and host servers. Is this correct and is there any special meaning to “host”?
- cluster - usually shown as a box around several database servers. But sometimes also around “hosts”. Sometimes a cluster manager is mentioned - is that a manager only and not data serving host? The variation in icons do not help clarify the role of these nodes.
- service(s) - sometimes you show only one icon and sometimes many for a given service. Are these supposed to indicate individual service instances (nodes) or a collection of nodes serving a service endpoint?