If last week was the skeleton of "servers, storage, and networking," this week we learned the "operations layer" on top of it — handling data, letting services communicate, and monitoring and automating the whole. Databases, application integration (messaging), management and monitoring tools, and IaC for building infrastructure as code. Today, with no new concepts, we review by tying these pieces together with comparison tables and selection criteria.
The core is still "when to choose what." The answer depends on the shape of the data, the form of the communication, and the kind of information you want to see.