Before we get into designing container diagrams we should talk about the difference between a model and a diagram.
What do you use to make architecture diagrams? Add notes with names of tools to a shared whiteboard. Put a plus marker by any which you have used.
There used to be an article on the c4model site about this, you can find it on the wayback machine. Similar material by the same author is outlined in an article about Structurizr.
The basic idea is that you can generate more than one diagram from the same model. A model is a non-visual artifact that defines elements and the relationships between them. When you use it to produce a diagram, you can choose which elements and relationships to show, and how to represent them visually. A diagram is a picture that shows elements and their relationships - usually some kind of boxes and lines. A second diagram that displays the same elements and relationships but does not share an underlying model may easily become inconsistent with the original diagram.
Structurizr is an example of a modelling tool. I found I could get a free account to try it out. This was sufficient to begin to understand what a modelling tool is and how it differs from a diagramming tool. Give people a brief demo of how to use the tool to create a Context diagram and where to find the documentation.
There is a starting position in the DSL with some styling set up, which you could give them.
Ask them to create a model that will produce the Context diagram which they came up with in the previous session Simon Brown’s 4C model - Intro.
If they have time, they could go on to model a Container diagram too.
Compare the diagrams produced by the different groups. If you like, show them a sample solution from the Instavoiced materials repo
Have them note down any facts they want to remember about architecture modelling.